An EV Motorhome : The Chassis

A look at the chassis of the motorhome.

     The Gulfstream-sunstream 2000 has a 34 foot long by 8 feet wide structure. To do anything meaningful one must work with facts and not rely on assumptions.

     Here we have the actual specs from the F53 chassis used to make the Motorhome. Shown on the diagram is exhaust manifold, catalytic converter, muffler, exhaust pipe and fueltank. Almost all the things we will be eliminating.

     Understand these drawings are not quite to scale. Area's marked in red can't be used (propane, Gen Set, and Entry Steps, Tank dump. Ones in green are our living space and storage. Blue is possible Battery & Inverter locations and pink is motor gearbox and drive shaft. Yellow is location of leveling jacks that flip down.
Bin 7 has the spot for the Gen set. moving back is where the old hot water tank was. This can be enlarged to service the purpose of holding the Inverter and master disconnect. Bin 8 is warm storage & our instant hot water and goes all the way across to bin 2. Bin 9 is electrical and cable storage and extends across to Bin 3. Bin 10 the dump station and two tanks that go all the way across into Bin 4. Bins 11 and 12 extend across to bins 5 and 6 respectively.

     To the left (left most image) shows a topical view of bin 9 & 3 green, Rear Wheels, and Bin 10 & 4 red. The right images space available. You can see from the top and bottom images that the bins extend across but are at a reduced height over the frame. The white box shows the heating duct which cuts into the storage space & the Blue shows space available for batteries. No space can be used where the wheels are. Pink is space reserved for the motor, gear box and drive shaft.

     While I'm at it, it is worth mentioning that the kickdown jacks front and rear are also going to interfere with Battery storage. In the front the jacks mount between the bins and the frame using space extending about half way back from the front of bin 1 & 7. At the rear they do the same using half the length of bin 10 & 4. The kickdown jacks are shown in yellow in the 2nd chassis drawing above. At the front they will not interfere at the back they very slightly interfere.

     Using lead acid deep cycle batteries At 12v @ 62A would take 64 batteries for 384v @ 124A and result in 5440 lbs of weight to achieve 47.6Kw of power. Using 47.6/2.166 = 22 miles and we would be 3626 lbs over weight. We have 288cu ft for batteries but only have 1844 to 2398 lbs of acceptable weight for batteries and solar panels.

     As seen to the left there are 4 basic types of battery make-up. To target 300Ah we need 750x 6A cells or 4090x 1.1A cells. During bank construction, with each cell being 3.2v, we can tap off at 12v; and 48v as we build the bank to it's 384v top voltage. We will make 2 banks switchable to make our pack for 384v @600A. I say switchable since we can run from 1 bank of 384v@300A while we solar charge the other bank. If both banks are to be charged we can't go anywhere and if both banks are fully charged we can run from both but then will need to charge both.

The LFP-G100 has is 3.2v @ 100Ah. It is made from 18600 @ 0.8Ah cells all tied in parallel. We can use the same concept but instead of 1 x 7 x 178 cells in parallel, we can do 2 x 7 x 15 in series-parallel to have 48v @ 84A using 32700 @ 6A cells. Our Gcell mini-pack would be 10” x 10” x 12”

    We wire the gcells in series and switch them to parallel to charge them. The LED lighting uses the 48v tap at 0.02A per light string. The 12v automotive systems draw about 10Ah. The computer control systems will use a 5v DC convert from the 12.8v tap. This maximizes the charge capabilities from both 120v AC and 48v Solar DC. Finally when parked we have 120v AC @ 45A from the two stage inverter should the shore power fail.

We will be going into the batteries in depth later.

Weight distribution

     The type 32700 lithium ion phosphate cell looks to be the most promising for ease of implementation, availability, price per unit and density of 6A per cell. But, and there is always a but, 3840lbs (over 1 ton) is way over the 1844lbs we have allotted for batteries. Clearly we must match available weight to the battery specs. 1844 lbs / 16 Gcells = 115.25 lbs ea. With cells at 0.32 lbs our cell count = 360.156 we use 360 since there are no fractional cells. It takes 15 cells in series for 48v so 360/15 = 24 cells in parallel. 1 Gcell = 48v @ (24*6A) = 144A. The end result is we need 16 x 144A Gcells to make 2 banks. The space required is 10” x 12” x 8*(30”) or 10”x12”x20 ft. With all things being equal, we can have 110.6KWatts with maximum range of 62.85 miles (104 km) without car in tow. We get 44 miles with car towed (75 km). Ultimately if we make Gcells 10”x12”x15” and pair them in a series/parallel fashion each gcell is 57.5 lbs 48v @72A. At this point everything is 100% balanced left to right and the frame weight class specs are ok. The majority of weight should be between the front and rear tires. Please note that this was an early spec for 72A Gcells which has been revised to 144A. Instead of 8) 10" x 12" x 15" Gcells we will go with 16) 10"x 30"x 6" for the full pack

The cockpit and everything engine compartment

     Where the engine was, there is an annoying raised Cowell inside. This can be removed to make the floor flat. to improve conditions inside the coach. Making an access panel in the floor at this point would open up into a void with front axles at the front of the void and a big space between the frame all the way to the back wheels to make building the boxes and mounts easier. The floor is 34 inches from the ground but back at the bins there is only 10 inches of clearance at the underside of the bins.

EV Motorhome : Drive Train

Drive train investigation

     Let us do investigation into the motor, gearbox, Inverter, and cooling technologies. We know that work creates heat. So if we expend energy to drive a motor fast, it will heat up because it is under load. Supplying that energy is an Inverter that changes Battery power measured in DC to alternating power called AC. The inverter therefore also will be working hard.

     Ultimately we want to move 10 tonnes (20000lbs) from 0 to 120kph (0 to 72mph) and we would like to maintain this for 200kms (120miles). Unfortunately, due to weight of batteries, we have a 75 mile max range (2/3rds of desired).
     The laws of motion do not change just because we are driving the motion by a different method. So the distance traveled by the rotation of a 22" diameter tire will always be 3.14 (pi) x 22 (d) =69.08 inches until the tire wears down to it's minimum diameter of 21.21 inches which means it only travels 66.59 inches.

    Mileage does not change either. There is 5280 feet in a mile and 12 inches to a foot. that's 63,360 inches to a mile. From this we can tell how many rotations of the tire are needed to cover the distance. (63,360 / 69)= 918.5. The differential uses a ratio of how many turns of the drive shaft it takes per rotation of the tire. We need to know this ratio as it will tell us how fast the gearbox output shaft must spin to make 1 rotation. Multiply that by the number of rotations per mile and we have the first part of the equation..

     From the above we now can work out rotations needed to go a specific distance and then work out the maximum time we want to take to make that distance. Our differential is 5:1 then we know the drive shaft spins 5 times to turn the wheel 1 turn and 5 x 918 = gearbox turns to go 1 mile = 4592.75. Rotations are counted in rounds per minute (rpm). There are 60 minutes to an hour. So if we want to go 1 mile per hour, we need to divide 4593.75 by 60 minutes to get the rpm. Which in this case is 76 rpm. to do the top speed of 72mph our gearbox will be rotating the driveshaft at 76 x 72 = 5472 rpm.

     With our former ICE engine it was probably rated at 1000 rpm at idle and when you tromped that accelerator down it could hit some red line at say 6000rpm. The faster you went though did not seriously increase the rpms. If you ever watched your tachometer, you would see it swing up to say 3500 then once you attained the desired speed it settled back down to say 2200rpm. I'm no ICE mechanic but to my understanding the engine had to build up the torque needed to raise the speed and once it had reached the desired speed less torque was needed to maintain it. In the days of manual gears, the engine rpm would be raised to attain the maximum speed for the lower gear then you would shift the transmission to the next gear and keep going till you were at your speed. The automatic does the shifting for you.

     So our ICE engine finally reaches 2200rpm at 72mph but from the above we know our example says 5472rpm = 72mph. this means for each ICE rotation we need 2.49 rotations at the driveshaft. The transmission in this case would have a gear driven by the engine meshed with a gear 2.49 times smaller at the output.

    Our electric motor operates slightly different than the ICE engine. For one, it's torque is instantaneous. Speed of rotation is determined by the amount of power it receives. Like red line on the ICE motor it has a finite maximum speed of rotation. The maximum speed of rotation of an electric motor must not be above the rated speed. So if the rated speed is 1500rpm it is safe to assume that it might do 1500 for a very short time but probably shouldn't be run continuous above 1400rpm. Our gearbox can be simple. It can actually have only two shafts each with a gear of a specific size. and for longevity we would put bearings on each shaft.

   In the gearbox shown to the left, the output shaft would need to mate with the driveshaft. Therefore the gearbox would be offset from center. Likewise the motor would be offset the other way. Where an ICE only turns one direction, an AC electric motor can be configured to turn either direction just by switching the main winding. So for this reason there is no shifter mechanism or the gears associated with such needed.

Now for my first found specs:
Transmission ratios 1 =3.11:1, 2 = 2.22:1, 3 = 1.55:1, 4 = 1.0:1, 5 = .71:1
Rear Differential rating 4.88:1 type Dana 80

Although these specs are for a 2012 model, it gives us something to work with. The Dana 80 differential is for a vehicle with gross weight 15000 to 18000 and ours is 17500 and has a Dana 80 differential so it's safe to presume the axle ratio is 4.88:1 and my rough guess was 5:1.
So 4.88:1 on 918 to go I mile = 4479.84 rpm
driveshaft rpm @ 1mph = 74.664
     At top speed of 72mph, driveshaft rpm is 5374.8rpm
     At local highway speeds here of 100kph to 110kph (60mph to 66mph) we need a motor that can sustain an rpm of 4479.8 to 4927.8.

     Most motors run 500 to 3500rpm as upper limits with 1500 being a go to standard. This would mean we need a gear ratio of our gearbox to be 9.855 @ 500rpm and 3.285 @ 1500rpm and 1.41 @ 3500rpm. But from the source "electric cars are for girls" they say Most AC electric motors run 230v AC @ 60 Hz and a top speed of 1750rpm. They also say that to create 230V AC from a DC source you need 340V DC from your Battery pack. Not to be thrown some curve, it's time to do more investigation. I tried to find some concrete facts about motors, torque, and weight classes they can safely handle but none could be found. So time for different approach we will review TV programs from "Jay Leno's Garage and web cast from EV west to try and get more info.

     The first of Jay Leno's Garage conversion programs was about "Big Bus Conversion" featuring the California based Electric bus Troterra Ecoliner Electric Bus
In this conversion it is a ground up completely electric vehicle.

At 18000 lbs empty and 38000 lbs fully loaded with people, it has a top speed of 55mph, but due to the route and application it normally travels 9mph with many stops. So in terms of weight, It is 500 lbs heavier then our Motorhome maximum weight when it is empty. When Full of passengers, it is 1.55 times heavier than our Motohome would be when we haul a car behind our rig.
     In terms of maximum speed, it can reach 55mph which is less than our desired maximum of 66mph but they say if they changed out the gearbox they could easily reach 70mph.

1. In service a day less than 2 years @ 24 hours a day. Suggests it definitely is dependable
2. With no tailpipe emissions, Atests to it being environmentally sound
3. It uses a very unique set of completely electric components like electric hydraulic pump and air compressor, and even electric grid heating.We will need similar remedies to compensate for loss of the ICE engine
4. It's about 7000 lbs less because it is a composite structure bus. So if they had gone with conventional aluminum body they would have had a empty weight of 25000 lbs. But this doesn't address the weight of their batteries.
5. maintenance is virtually nil cause there is no oil to change or anything of that nature. Definitely as I expected.

Construction

1. The composite material is basically fiberglass inner and outer with resin injected balsa core. It is 4 times lighter than metal and twice as strong as metal. Ours is fiberglass top half but with numerous built in walls, appliances, cabinets, etc. but does not have the rows of seats with aluminum frames
2. There are no steel components to this bus except the suspension. Ours has outside steel bins front to back on both sides
3. It having fully composite structure which is non-conductive makes the whole bus safe for driver, passengers and maintenance. Extremely high voltage through parts of the bus is kept away from everyone. The planning of ours also intends not to pass high voltages and currents anywhere inside or accessible to people

Drive train

     I fully grasp what they said about the EV industry going with single speed transmissions because geared transmissions just fly apart under the instant high torque of electric motors. They are using a modified 2 speed transmission so they can run low speed for route pick-up and drop off but switch to high speed going inter-route. It makes sense for their application. for the motorhome, a single speed would be more sensible. Gearing requires a auto-clutch and if you have ever had a manual clutched transmission, it is prone to damage even on ICE if not properly clutched. I originally planned a two shaft two meshed gear transmission with engine and drive shafts offset but am now thinking to run an input shaft with large conical gear meshed with two parallel shafts conical gear at both ends and conical gear output shaft to cut torque stress by 50%
They are claiming a 200 HP Motor.

Charging

1. I was surprised that they are using 12v Lead acid for internal functions. At 4 x 85lbs to run lights and accessories and running a separate inverter to recharge the batteries adds a lot of unnecessary weight. The main drive uses Lifepo4 battery packs so switching the house batteries to match would mean they could cut weight by another 300 lbs and share the same charge system.
2. Charge stations along the route charge the batteries from a gizmo mounted on the roof. A 90% charge in under 10 minutes.works for them because of the fixed route but for the traveler, the best we can do is continuous charge from solar availability
3. - In the shop is a power charger that takes an hour and they can also plug a utility charger in to charge conventionally over 8 hours. I wonder if they get a quick 1 hour charge because the batteries would seldom have much used but then they say conventional charge is 8 hours which is more feasible given Lifepo4 should never be charged faster than a 1C rate.

Batteries

     Nothing is specifically said about Batteries although they do say system runs 360v and KW of 217KW which computes to about 602Amps. Lifepo4 are standard in 100Ah, 200Ah, and 300Ah as 3.2v Gcells so the # of cells can be estimated at 2,3,or 6 parallel banks of 113 cells and a weight of 4600 lbs.
     If indead they are using 3.2v @ 300Ah Gcells then they have 113 Gcells in 2 parallel banks which is great for making huge packs but not great for charging or battery replacement.

Brakes

     When the foot comes off the accelerator, the regen slows you down.
Conventional brakes 20000 miles, originally expected 100,000 because of regen but looks like it could push 500,000 miles.

    In this episode, Jay speaks with his guest about a different type of bus conversion.
For the price of the previous bus with all it's fanciness, you can convert 4 of these. 1996 new flyer bus. they buy as an old worn out bus and refurbished.
The bodies are fine but the drive train is toast so it is discarded.
These are ideal for routes of 100 miles or less

Drive train

- The motor is about 15 inches across and maybe 20 inches long and is 170 HP with about 1200 ft-lbs of torque
- It is direct gearing and NO transmission.
- Virtually no maintenance, no oil changes, fluid top ups, filters etc.

Braking

- more than double the brake life. It is full regen braking.

Batteries

Tear Down :Out with the Old in with the New

     In this chapter we will go over the three areas of concern. The front canopy or engine compartment, the rear fuel tank area, and the interior dash. We will be discussing and showing the removal of things that are no longer required. Then we will discuss and show the implementation of things needed to be added.
     The canopy is the containing compartment for the engine, transmission, starter, water pump, air conditioning pump, steering pump, Air intake, battery, carburetor, exhaust manifold, and alternator that we will be removing. We will be keeping the Radiator, Fans, Windshield washer and reservoir, Radiator overflow, Electrical distribution, Power brake system, Power steering system, and from the front axles to the front drive wheels. We are adding the electric motor, Power Drive inverter, And electric pumps for water, steering, air conditioning, and brake vacuum.

Engine Removal

There are three ways to remove an engine from a motorhome.
1. Take from the top,

• Pull drivers door
• Pull steering column
• Remove Drivers Seat
• Remove doghouse
• Remove as much as you can from block
• Support Trany and disconnect trany
• Wrestle Engine up and out door.
• Go into cavity and clean up anything left behind
• Make trap door over opening
• restore driver seat, steering wheel and drivers door

• Jack vehicle up and place on stands
• Pull Front steering
• Remove doghouse
• Disconnect anything holding above
• Support Trany and disconnect trany
• Remove cross support
• Drop Engine out of bottom.

• Remove bumper
• Remove front grill work
• Remove doghouse
• Dismantle attachings from above and from the front
• Support Trany
• Disconnect Trany
• Drag engine out the front

** It is important to take steps to both measure distances from all sides for drive shaft alignment and / or secure the drive shaft at the correct alignment before removing the transmission.**

This above step will help when the drive shaft is shortened and the motor is aligned for mounting.

Part one: Drive shaft Removal

     Locate 4 bolts at the rear differential which may be 8mm Hex head or torx and the remove the retaining brackets that seat the u-joint into the yoke.

    Using a crowbar between the coupler and the joint pry the u-Joint out of the coupler.

Replace the brackets for later reassembly once the drive shaft is shortened and mounts are in place for the electric motor.

Step two: E40D Transmission Removal

        
     
        
        
  
     Being a non-mechanic the steps to remove the transmission are in image form. Essentially, you want drain the transmission of fliud, disconnect the battery, gain access to the the flywheel, Rotate it to access the bolts , remove the bolts holding the flywheel in place, removine linkage and cables, support the transmission, remove the brace below it and drop the transmission.

Step three: Shortened Drive shaft

     This can be done either as a temporary shaft replacement or a permanent replacement but for best results you should visit a licensed drive shaft shop and have one made special. You will need in this case to measure the length needed, the yoke diameter and U-joint size.
        

     Mark a centered line length ways down the shaft. This line will be used to realign the shaft ends for re-welding together. It is important that the ends mate in the same balanced linear alignment after the section is removed. Do not cut too close to either end of the shaft.

     With the marks in place line the shaft absolutely level with-in the crop saw. Take care not to misshapen the shaft by tightening it too much. The shaft thickness is very thin walled.

     Cut, debur and polish the end being kept so a good strong weld can be made to rejoin ends. Repeat for the other end.

     Here we realign the ends and tac weld them temporary so we can check trueness. Welding will tend to slightly bend the shaft.
  

     Using a point gauge rotate the shaft looking for as close to zero deviation as possible. only when 100% true can the shaft be welded permanently.

With the drive shaft out of the way and shortened, locate all exhaust components like tailpipe, muffler, Catalytic converter, exhaust ‘Y’ and remove them as they are no longer needed.

5.Transmission removal

Engine must be out to even attempt to remove the trany.

• Disconnect the linkage
• Disconnect from Driveshaft
• Disconnect mounts and either take out through doghouse opening or raise vehicle and drop out the bottom.

6 Gas Tank removal

1. Remove the hose clamps on all lines
2. Siphon out all fuel. 0 to 500 lbs
        
3. Support the tank and undue two straps bolted either end. Bolts have a tendency to rust solid so WD-40 or penetrating oil may be needed. If you get impatient just cut the straps.

     
4. Tilt down the tank and remove all electrical and line ends and take out the tank. 50 to 100 lbs
5. Clean up the old tank area and take good exact measurements between the frame rails, and between the bin backs and the rails.

Engine Compartment

Well it's not really the engine compartment anymore...
So what are we doing in here? We are going to remove the radiator, Wiper reservoir, coolant reservoir, Batteries and their shelves, The transmission cooler, Oil filler, transmission filler and the A/C unit.

Once all has been removed, the area will be power cleaned.
We will then locate and place all brackets for our stuff to go back in then prime and paint blue.

        Hard to see but has battery, oil filler, AC, Radiator, the battery (2 of them for engine and 3 for coach) won’t be needed as the power will come from our battery packs. The AC unit was removed from the engine and strapped out of the way for remounting with an electric motor.

The Radiator will move to the front just inside the grill and the hydraulic pump remains where it is.

Cleaned up with opening for new HVAC and shows the engine access where the radiator was. On the other side we have transmission filler, washer reservoir, electrical box, brake booster and steering unit. Cleaned up with steering and brake units not shown. Electrical box will be remade.

An electric water pump will be used from the radiator to the AC unit with a tap for cooling the motor and Inverter.

Electric brake booster vacuum pump is also

added

Electric power steering pump is added.

Cockpit changes

Here we are going to remove the doghouse and remodel things so we have a flat floor with access panel. Before and after views

LED custom lights

     My first ever custom EV-Motorhome should be heralded as unique so Lets start with a copy of the Kitt-car LED EYE that strokes back and forth as the vehicle travels or when Four way flashers are on. In my E-Trike project this was introduced as part of it's front lighting assembly. Now the turn signals will be made separate. The control board will be the same.

     11 LEDS will be fit into a clear epoxy frame which is sealed against harms from weather. The frame is made from a clear drop ceiling lens heated and formed into an open front box. Then Led circuit board is placed into the 5" x 0.5" x 0.75" box and filled with epoxy resin. Another clear lens is glued with acetate glue to the top only after the epoxy has dried hard. Two mount screws holes are then drilled either end. The 12 wires coming out the back then wire to the controller.

Marker lights

     Unlike the E-Trike, the motorhome has more than just 2 front, 2 back, and 2 side marker lights. It has 4 side marker lights with 2 sets front and rear and 5 at front roof top and 3 at the back roof top. We will have 2 series strings of high luminence LED's with 48 Leds per string. Each LED marker assembly will be 4 Leds along the sides and front and rear with 6 LED's at the roof tops. These Marker lights are made in the same way as the Kitt-car EYE was.

At the back we have these combination lights with turn signals, Marker, and brakes with 40 LEDs for turn and brakes. The front will not have the brake LEDs. So instead of 6A being used at each marker and signal and brake light we are using 0.02A for markers, 0.02A for signals, and 0.04A for brakes. The license plate light will be white LEDs tied in with the Marker lights. A Sonalert beeper with 2 white LED units are used for back-up.

Coach Control

The coach system has Taken on the duties of Charge control of the batteries, Solar array control for adding solar charging and tilting, Bin heating, Water supply management, Floor lights and Distribution. Originally planned into the dash computer but now to it's own home as a coach control system since the features function when parked and not when driving. There are eight touch buttons to access the different systems.
     The breakdown of it features are as follows:

1. Battery ... current state of charge of each banks of battery
2. Camera ... Record and playback of Dashcam and Rearcam
3. Charging ... Select where to charge from and status
4. Lights ... turn on/off interior/exterior/floor lights
5. 120v AC Power ... Select source of power : Shore/Gen/Battery
6. Solar ... Control charge on/off
7. Water ... Bin heating, Instant Hot Water, Pump/City
8. Shutdown ... turn off the system

Power Center in the coach

In my coach the main power center sits below the fridge. It consists of a breaker panel, 12v fuse panel and a charger of 3A for the coach batteries. Totally inadequate for the new EV motorhome.

Campground power is usually 15A/120v, 30A/120v, or 50A/240v. The last one is separated in the unit into 2x 120v/25A circuits which split into 4x 12A circuits. The 30A/120v is separated into 2x 15A circuits. To make use of all methods of supply we would need a 230v/50A input added and a new breaker panel.

Seen here is the original power and distribution panel that sits below the refridgerator. It housed a trickle charger for the coach batteries, master 30A breaker, 5 services breakers, and 9 x 12v services fuses.

The bottom is the charger and the top has the distribution. It's the bottom part that has to change.
The Inverter/converter will have 120v-15A AC, 120v-30A AC, 240v-50A AC as input sources. It will have smart charge output 57v DC to charge the battery Packs and the battery packs will have 12v DC for the 12v appliances. It will even have a solar panel input, and it also has 5000watt Genset input for 43A @120v AC. The 30A Main coach panel will get it's power from the inverter/converter as will the 15A water heat system. As long as we are connected to shore power by one of four inputs (AC) coach operations and batteries are charged till full. If AC fails, the converter immediately switches to the EV batteries to keep things going and if it becomes drained too then it starts the gen set to power things. However, limits are present, The genset can provide only 10 hours under full load, The EV system can provide only 40 hours under full load so we had better hope main power is restored with-in 50 hours or all stops.

There are 3 more functions to this system. Auto controller signals for connect "Coach to Chassis", "Run Coach from Battery", and 12v DC distribution complete the distribution control board.

The circuit to the left takes 5 different AC charge source systems and feeds them in one pair of SCR's per source. The gates of these SCR's are tied in full duplex mode to trigger signals coming from the GPIO80 & Automotive controller to turn on the selected source. Once on, the source remains active until it gets a charge full reset from the charging circuit. In addition, the 15A, 30A, and 50A systems tie into the coach AC Distribution Panel such that both the 15A and 30A systems can be active to supply the coach power requirements, or the 50A system can be fed into the system to supply these coach needs. From the 15A/25A feeds, we get an internal switch for selecting bin heat or Instant Hot Water. Actual control is likewise controlled by 3 enable triggers that are also reset by the full charge reset. The water pump is controlled by a final GPIO80 trigger.

And this will run from our new Coach Computer with touch display. The 120v system will still use the Breakers and 12v fuses to their respective systems but, two new breakers are added for the bin heat and solar array systems.

The coach display unit

     To keep wiring needs to a minimum, the display will be fit into the wall at the Fridge since the space under the fridge has the current breaker panel which will be replaced to house all the system electronics. If I did this, all the coach systems would be almost localized. Two systems for the coach are still not planned in. The Entry step control, and the floor lights are currently in the dash system.
     I am abandoning the multi shore charge sources as overkill. Not all RV parks have 50A service, and no parks have 300A service to date. 120v AC @ 15A and 120v AC @ 30A are standard. The 3000 watt to 5000 watt GenSet will be propane supplied instead of using gasoline and will tie in as a third power source for the 120v AC. The fourth source of AC is pure sine inverted from the battery bank(s). So we have 4 sources of AC feeding our 120v distribution to the coach.

    Looking at the charge side of things, the 3 AC coming from the shore power and GenSet feed a 120v to 60v transformer which after rectification is 57.5v DC. The Solar array of 19 x 1A panels provides 57v DC @ 19A charge. Both charge sources can be fed to either or both battery banks. In charge mode a bank is switched from 8x 48v series blocks to 8x 48v parallel blocks. There are 2 banks. A bank not being charged can be used to run from. When running from battery, the series blocks make up 384v which feed a pure sine inverter to supply 120v AC @ 30A. Each bank has 2 coulomb counters. One in each bank counts discharge from the 384v run mode. The other one in each bank counts charging. The coach computer therefore can check when batteries are fully charged or discharged and take action.
This alleviates running several banks of batteries of different voltages or doing any dc to dc conversion.
     Like the Auto Controller of the dash computer, we will be using a distribution board with daugther boards. GPIO-1a, GPIO-1b for Enables, GPIO-2a, GPIO-2b for lights. GPIO-3b is input digital sense and ADC-1 is analog temperature. Solar tilt is no longer included.

    Looking at the left chart, 15A service supplies the bin heaters and IHW. If no 30A is available it also tries to supply the 30A side. The 30A service supplies the whole coach except for bin heat and IHW unless no 15A is available. If neither is available or they have been shut off, the GenSet connects to both systems. Selecting run from Battery disables all other sources. When charge Bank A is on Bank A switches from Run to charge mode. When charge Bank B is on Bank B switches to charge mode. If both banks are in charge mode you can't Run from Battery. Enable shore charge turns on the charger until either manually shut off or the batteries are full. Enable GenSet charge turns off shore charge and attaches the GenSet as the mains.

** The solar tilt and cover feature was abandoned due to complexity and weight so the GPIO32 functions are moved to the RPI 3 module and solar motor control removed.**

The GPIO-3A/B group of outputs control the solar array. When open solar is selected solar panels are uncovered and recovered when open is off. Enable solar connects the solar panels to the charger. If the batteries are charged Enable solar is turned off. The next 6 items control the solar tilting

    The second chart has provision for lighting control.
     Next we have the input items these inputs read hall-effect sensors on the panels to signal when panels are at a specific location. Lastly we have two temperature sensors that provide for cabin heat and Battery heat values.
     As you can see the coach system layout is quite different now. In Grey we have the original with two sources GEN & 30A. It had a 120v AC to 12v DC charger @3A. Now we have Selectible Source for AC, a considerably more powerful DC charger @60v, can run from battery if necessary, full charge monitoring, and solar charge all under computer control with touch display.

    The wall at the fridge has 9" of space for mounting the width of the display and we must stay below 4" of depth.

     The RPI has many 7" Touch screens available for it so we can meet the width requirement. A 7" Display is roughly 6" wide by 4.5" tall and 1" Thick. The raspberry mounted to the back is another 1" thick so we are under the 4" limit. The enclosure will have to be determined based upon system space requirements. Instead of adding a 5v 3A power supply we will use the 9.6v tap and regulate to 5v.
    Power for our bin heat and instant hot water was ran from a separate 15A 120v feed which could be plugged into the exterior passenger side connection if the campsite didn't have both 15A and 30A power available. In the above depiction, we have almost got the system planned the way we want it but, and there is always a but, there needs to be a means of connecting the 15A to the 30A when either the 15A or 30A is not connected. Without such a bypass, you would need to go outside and plug the 15A line into the external socket of the 30A system. Not ideal, as it only solves for missing 15A service.

    Charger module When commanded by the computer, enables Battery bank 1 and or 2 for charging. Whatever bank, if any, that isn't selected becomes available for the coach. Charge can be directed from AC or the Solar array.

     This was our original charge module for the EV Motorhome. It had a single coulomb counter for charging/discharging one or two banks. Because we are having the charging system handled by the coach system when parked and by the dash computer when driving, we need to modify this system to have two coulomb counters (one for driving/regen and one for charging one or both banks. The coach 30A connection needs to be tied to the 30A breaker panel rather than have it's own separate plug-in. Lastly, it won't do to connect both drive system and the coach system in parallel without some intervention.

     Of the pins, pin 8 (AC En) is exclusive to the coach system. Pin 13 goes to a latching relay powered by the coach system that must connect the other pins to one of the control systems. Pins 1 and 14 are powered by the Battery pack at .001mA when neither system is engaged and up to 20mA when either system is charging or running. Being that we can hard wire the board for interrupt design, pins 2 and 3 aren’t needed. This leaves us with 4 Enables from the selected computer control, 3 interupts to either computer and a directional POL signal to either computer. They are all logic level signals so we could use 74LS244 bus transciever chips to separate one PC from the other.

    When I designed the Dash system which originally was to control the coach systems, I had the dash send signals to the Source system to select which source to use for powering the coach and which to use for charging. These went to latching relays so that when the drive computers were off the latch relays maintained settings. But, and there is always a but, to make a change one would have to start the vehicle and since only 1 or two connections would be active at any time, it doesn't make sense to use IGBT's (28 of them) for switching sources.
28 SCRS were used to create 14 AC pathways that can be individually controlled. 5 paths provide choice of AC run source, 3 provide IHW and bin heat control, and 6 others handle charging distribution. Note that because of high currents possible during charge cycles, 4 SCR's are used for each Pack. The main charging Inverter/converter has 3 Battery state of charge sensors, 190A @384V charge and a 95A 12v charge. The converter has 384v DC to 120v AC pure sine wave inverter.

     WOW! what was I thinking. 95A is enormously dangerous at 12v DC but almost 200A at 384v DC is criminal and extremely expensive wiring. The cables alone would cost over $2500 and the protective circuits would need to be custom and could run $10,000. Converting to a 48v system throughout with up to 60A charge is so much better. True I don't get 1.5 hour charge time but I gain safety, available parts, and almost nothing in costs.

So our new charger control needs to have some additions but is functional in concept.

    Our new distribution system has 2 shoreline sources, the Gen Set and Pure sine wave conversion of the 240A 384v Battery. A 10 Breaker panel is needed for the system. The Gen Set contactor and 120v AC sockets are the only components of distribution not to reside with the breakers. Behind the breaker panel is the charge and inversion systems. Rather than make a converter from 48v to 12v I simply tap 12v off the lower 4 Gcells of Bank 1. This gives me 12v DC and cell balancing should have no problem topping up string 1. The Sine inverter, DC charger and Coulomb counter will reside under the Fridge in a drawer with the breakers at the front. Two High voltage high current line come into the drawer (144A 384v, & Traction Supply). The 120v AC line from the Gen Set will feed into the drawer to a contactor and then pass on to the distribution panel.

EV / MH power center

    The power center is now radically different from the original design which tied charging, coach operation and vehicle drive into one massive inverter converter. It is a far better plan we have now. Keep the Driveline separate from coach and keep high voltage and currents out of the living area.
     Five systems that work independently and together. The main Battery banks have independent shutoffs, with 3 Master shutoffs. Master shutoff 1 works in conjunction with the Inertia Switch and either can cut out the 384v 144A Battery system. Master shutoff 2 kills 12v power @ 120A from the Coach system. Master shutoff 3 kills 12v @ 120A power to the Dash and automotive systems. The Propane has a Shutoff at the tank to stop both the gen set and Coach appliances from operating. The coach system has a maximum run time of 24 hours during a power failure. This is paralleled by the Dash and automotive system with a 300 hour run time if not moving and of course shorter run time if driving. The traction system has the highest demand with a travel range of about 65 miles.
     Ideally, the solar array and Batteries are not considered systems as they are dependent on other systems to function.

Coach Software

When we get to the screens again we will show the look rather than a huge amount of code used to define them.

The main screen is a simple 8 button menu

     The coach system is powered by a simple On/Off located at the base of the panel. When turned on, The raspberry PI does it's start-up and presents the above screen view. There are 7 displays selectable by the screen and a shutdown button. Current date and time display along with system messages.
This routine has the timeout code added to it to both initiate date and time function and also to allow interrupt processing to be done. Where the Interrupts functions with-in micro-seconds of an event to capture and set values, the handlers are called every 10 mili-seconds to take care of anything that has happened.

In coach mode the coach has control, in motorhome mode the drive system gets control. As can be seen either or both battery banks can be selected for charging.

  There is provision to control all lighting from this panel display. Many motorhomes have the light switches at the ceiling. Short people and children can not reach them there. This panel allows more comfortable light control.

     The charge Display shows the number of ticks for the selected Battery Packs defined. The minimum ticks is the recommended minimum that leaves 20% charge in the Battery Pack. The Max Ticks is the top charge of 95%. Battery use between these limits is acceptable for long battery life.
     Current battery charge in ticks display while charging or discharging by way of running from battery.

The video record and playback screen

   Selection of the Water option provides control over bin heat, (so water doesn't freeze), Instant hot Water, ( on in summer, on when used in winter),Line heat ( in winter so water supply does not freeze), and Pump (on for internal water off for city water.)

     Two ZC Triacs control 15A AC supply to each of Bin 8 bin 10 IHW and Line heat. A 12vDC SCR Turns the pump On/Off and the City valve Off/On. Three Temperature sensors read temps at the locations.

And finally, you can change between F or C for temp readouts.

    The solar array tilt has been eliminated.

    Choose AC Pwr to direct the source of AC power. You can source AC 15A and AC30A at the same time, Source AC 15A and Genset at the Same time. Source AC 15A and Run From Battery at the same time. No other combinations are valid. As you change the AC source the image changes to reflect what you have done.

Battery space planning

    Here I am trying to demonstrate that there are options to how you organize the batteries into packs depending on your particular set-up. For me I am still trying to find a motor / inverter powerful enough to handle the load of the motorhome. I don't have definitive answers at this point from any sources so I have to keep my options open.

    For each vehicle there will be differing dimensions these are for my unit. Between the frame rails and the bins there is 8" , the rails are 5" wide and 9" high spaced 34" apart

    Working right to left (back to front) there is 121” of space between the bins and the frame on both sides. Between the frames is 34” with a tire cavity of 41” at the back. Then there is an 80” x 34” cavity for the fuel tank. Next are the rear axles followed by 86” of space between the bin and frame on both sides. Between the rails is 34” x 234” of space from the rear axles all the way up to the front.

    The bins themselves are 23” high x ~41” wide x 18” deep. The top 10” pass through to the bin on the other side. With 8” between the bin and rails. Battery space is therefore 207” L x 8” W x 13” H on each side. Accommodating 10”x10”x6” Gcells @ 42A ea. We have room for 20 per side. 8 Gcells per Bank = 1.5 banks per side. The 80” x 34” fuel cavity has potential to hold 8 rows of 3 Gcells 10” x 10” x 12” = 3 banks of Gcells @ 84A or 12 rows of 10” x 30” x 6” Gcells @ 144A = 1.5 banks.

    So we can have 2 banks of 42A Gcells between the bins and rails either side and 2 banks of 84A Gcells in the gas tank area. Driver side rail Gcells wire in parallel with Gcells on driver side of fuel tank area for total capacity of 126A per bank (252A Pack). We could also do 1 bank of 144A Gcells in fuel tank area and do 4 x 144A Gcells on each rail space as the second bank for a 288A Pack system.

2 banks 42A = 84A Pack 544lbs 13 miles/charge

2 banks 84A = 168A Pack 1088lbs 26 miles/charge

2 banks 126A = 252A Pack 1632lbs 39,5 miles/charge

2 banks 144A = 288A Pack 1843lbs 45.13 miles/charge

    These figures are based upon a fully loaded trailer with car at full weight capacity of trailer. On a 144A per bank system there is a potential to 8 of 10” x 10” x 6” 42A Gcells in the fuel tank area which would increase 1 bank to 186A while the other is 144A. The weight becomes 2112lbs. 51.72 miles/charge. (102km). Without solar charge we have 2395lbs available for batteries. With 22A Solar we have 1757lbs available. With 19A solar we have 1844 avabeilable. With 2112lbs of battery we can have 10A of solar charging.

    We are not using any space between the front canopy and the rear differential between the frame rails for batteries.

The last 330A system does put 1620lbs behind the rear tires and 500lbs between the front and back tires. If we move the rear 4 144A Gcells up with the front 4 Gcells weight is more even but we are using 12” of our 34” width between the frame rails for battery placement.

Generator System

    This will be replaced with a propane 5000 watt model and tied to the custom inverter / converter. The gen set can be started manually, by the auto-start/stop at the Coach control center, or automatically by the EV power converter. Under full load it can run for 10 hours. It can provide 74A @ 48v recharge = 1 bank 144A Gcells 50% in 10 hours.

Coach house Inverter

    The inverter bay was formerly where the propane hot water tank was. It will now have the Genset transfer switch, Cutoffs for Banks 1 and 2, and a pure sine wave 60 Hz Coach inverter that will upon command convert 48v DC to 120v AC @ 30A 7000w. 29Hours run time per bank if using 144A Gcells. Figures assume using full load @ 30A.

Install &wire the Inverter transfer switch and cutoffs

    The 7000w Inverter has a remote enable from the coach computer. When run from battery is selected, you have a choice of Bank 1, Bank 2, or both. The computer then configures the 8 Gcells of each selected Bank into parallel. The 48v charger line becomes the 48v Inverter line and is passed to the pure sine wave Inverter which gets an inverter enable signal and 120v Inerter output goes to the coach system controller.

    The Genset has a remote start/stop Relay run from the output from coach computer, and a high power solenoid also run from the coach computer. The solenoid when activated transfers the 120v AC from the Genset to the coach system controller.

    The Inertia Switch connects between the two 384v bank cuttoff switches. It feeds up to a master cutoff switch under the drivers seat and from there to the Traction Inverter. If the Inertia switch trips all power from the batteries is cut off until reset. If the Master shutoff under the drivers seat is off, again all power is cut off. If either Bank shutoff isn’t in the run position that bank can’t be used for traction drive. Down at Each bank of batteries is a crossover board. It has a series of high power Mosfets that pass 384v to the appropriate Bank Cutoff Switch. The Mosfets get a computer signal to enable 384v drive for bank 1 or bank 2 or both. The crossover board also has Mosfets controlled by the computer to configure the 8 Gcells from series to parallel for charging or run AC from battery modes. In this case the 57v charge line either feeds 48v to the Coach inverter or gets fed 57v from either the 120v to 57v charger or the 57v Solar array.

Install &wire the Motor

The Motor and traction inverter get mounted at the back closer to the differential. A shortened drive shaft connects the differential to the motor shaft. The motor secures to the frame rails as does the Traction Inverter. There will be 3 heavy phase wires from the Inverter to the Motor and 3 to 5 light sense wires as well. Two low power enable wires, 3 low power accelerator wires, 3 wires for FWD / REV Selection and two wires for 384v supply go forward to the Master shutoff and canopy controller. In this manor all high voltage and high currents remain away from all human occupants.

EV Vehicle< Solar Charger system

Adding solar charging to any EV vehicle could be a great feature for us to have. Ideally, you want to have 57v to charge a 48v Gcell. In run mode the Gcells are organized Pack voltage/3.2v to make the voltage in series by Pack Amps/cell Amps in parallel. This is how auto-makers make EV. Pack voltages range from 312v to 460v in Auto-maker EV. Pack amps range from 300 to 600 Amps. There is no hope of adequately charging such high100.00% voltage from Solar on a vehicle.

    We want the most affordable way for people to get an EV so we go with 48v Gcells that are comparable in size to a standard lead acid battery, less than half the weight, are owner replaceable, and come in sizes 42A, 84A and 144A. Wire 8 Gcells in series and you get 384v @ 42 or 84 Amps, 144Amps. Call that a bank. Make an identical second bank. The banks now wire in Parallel and you have 384v @ 84A or 168A, or 288A. Add an electronic switcher and we can now run from one bank until it is depleted, switch to the second bank and continue to run from bank 2 but the depleted bank can be solar charged. When a bank is switched to charge mode the Gcells reconfigure into Parallel. As a Parallel set of Gcells the Amps add together so a 42A Gcell becomes 336A for charging, 84A Gcells become 682A and 144A become 1152A. From 15A shore power, charging is 57v @ 37A per bank (9, 18, or 31 hours). If we can get Solar to charge at 40A, you could drive to work park and work your 8 hour shift and drive home on bank 2 because bank 1 still has 12minutes left on it’s charge cycle. Once home you plug in to charge bank 2 or you can go back to work the next day charging bank 2 then switch to bank 1 for charging it while you work. This works if there is nice sunny days to never have to charge if your travel less than 32 miles to work.

When there is insufficient sunlight the solar panels need a blocking diode to prevent battery pack discharge. A Coulomb counter at the switcher keeps the computer informed of the battery state of charge. We now know the ideal situation but life is not ideal. Vehicles have different roof sizes with differing obstacles. A sunroof or roof rack or rooftop carrier can spoil things quickly.

1. Small car 1728sq in. (4ft x 3 ft) [1panel]
2. Regular Truck no canopy 1152sq in (4ft x 2 ft) [2 panel]
3. Regular Truck w canopy 5750sq in (10ft x 4 ft) [5 panel]
4. Mid size car 2880sq in (5ft x 4 ft) [2 panel]
5. Large car 4320sq in (6ft x 5ft) [3 panel]
6. Crew cab 2880sq in (4ft x 5ft) [2 panel]
7. Class A Motorhome 22,464sq in (2 x (3ft x 26 ft)) [19 panel]

    Using the chart at the left we see that for the desired voltage a 1A panel 4ft x 2ft gives us 57v so a small car or regular truck can only have 1A charge so we could get 8A during a day while at work. 2% of what we used if we used 42A going to work. The 1A panel actually can provide 2A if bright sunlight. A truck with canopy could have 5 panels or 5A for 40A recovery 12%. A mid size car or crew cab could have 2 panels or 2A for 16A daily recovery. A Large car 3 panels or 3A for 24A daily recovery. And a class A could with a little tweeking have 3 panels across roof x 6 rows down the roof or 18 x 1A panels. We might even be able to squeeze a 19^th panel.

    Panel weight is roughly 29 lbs taking into account plywood backing, u-channel, Lens and polychrystaline cells. These weights need to be included in the conversion calculations.

    If we presume a small car 4000 lbs including 384v @ 42A battery banks. We get a 32Kw Pack so our total range is 32/0.4 = 806 miles. Average person drives 32 miles per day according to insurance bureau of Canada. Technically, we used 3.33A a day for two way travel. So from bank 1 we used 1.66A getting to work and Solar recharged 1A over the day. By the time we get home we will have only used 2.32A so shore charge becomes 1.01A x8 = 8.08A/37A = 13 minutes or $0.08 from the power grid @ $0.17/kwh.

At the other extreme we have a 17000 lb class A motorhome pulling a trailor 24000 lbs with 384v @ 336A Pack. We get 129Kw Pack with total range of 129/2.4 = 53.75 miles (89.5km) to jump between campgrounds 70km apart. With average travel time being 1.5 hours or less we get about .75 hours recharge of bank A or 1.78A of the ~300A used. While camping we can recover 17A during the day and switch to shore power to recharge at 37A over the next 7.6 hours for about $6.12 if they charge extra for power. That’s it cells are charged ready for next move. If we loose shore power our rig can run from battery for 8.4 hours on inverter assuming we are drawing 30Ah or longer if draw is less. And we can solar recharge or Genset recharge.

    Our coach monitoring system in a motorhome application will handle the charging to make sure an over charge does not occur. Essentially, once charged only driving the motorhome or handling a shore power failure will deplete the battery banks.

Panel Planning

    Our roof space is a total of 30 feet by 8 feet. This space is occupied by 2 skylights 2.5 ft by 1.5 feet, two Ceiling vents 14 inch square, 2 airconditioners 16 inch square and 2 exhaust vents. So 240 sq ft reduced by 20.5 sq feet. So maximum space for the solar array is 220 sq ft. This can accomodate 3402 4 inch by 2 inch polycrystaline solar cells. We need to obtain 57v per panel which at .5v per cell means we need each bank to be 114 series cells. A 4 ft x 20” is needed to accommodate 5 strings wired in series for 1A. All Panels wire in Parallel to give our working Amps. Across the front we get to have 4 panels then down the outside edges we get 6 each side with 6 split panels (3 rows in one and 2 rows in the other) to give us a total coverage of 22 panels or 22A total.

Acquiring 2508 cells + 5 sheets of ½” plywood will cost about $1005 plus the lens and trim $88 and $396 respectively. Total cost $1489. The solar array wattage is 1254w. Panel weight is about 29 lbs each. 638 lbs for 22.

    The panels being on the roof and in the open means they can suffer damage from snow, hail and tree branches or other debris. Coming inside the coach we need a control center for the charge system that must handle 120v AC @ 30A & Solar charge, and Genset charge. The Charge control system also handles the distribution system. So ideally, it needs to convert 48v DC to 12v DC for the furnace, c.o. detector, fridge, 12v lighting, water heater, & water Pump. (note: on my rig the fridge and water heater don't use 12v). It also must handle 120v distribution to the 5 systems connected to the breakers. Our system therefore will need a Raspberry Pi and a monitor with touchscreen, a controller, and an inverter/converter/charger unit, and the distribution panel. In this way we can handle shore charging, solar charging, handle 12v - 48v - 120v systems for a true off the grid experience.

    This brings us to the last part of the plan. We must collect all the energy from the panels and get it down to the controller and subsequent battery banks. We know from the above details that we could have as many as 22 panels of 114 cells. Each panel producing 57v @ 1A. There is nothing that says we have to arrange things this way. We could just as easily organize them into 4A or 6A or 8A panels. The difference would be just the number of cells per panel and how they are wired. For each 4 inch by 4 inch square we are producing 1v @ 1A. Panels wire in parallel resulting in just 2 wires making the journey to the charger.

    The roof has 3 area's marked with an 'X' these are to be eliminated and returned to normal roof space. The smallest one was for venting the old propane fridge which is now electric. The two skylights have never been useful they only serve the purpose of letting water leak into the coach, and making the coach hotter in summer and colder in winter. Before I blocked them off from the inside, we had temps 10 degress higher in the summer and temps averaged 15 to 20 degrees colder in the winter. In one case we had to run the AC more and in the winter had to run the furnace more. Both situations can be expensive.

    I had made elaborate plans for an auto tilt servo system but have decided against it due to complicated construction and control and huge added weight.

     Looking back at the roof, if I do get rid of the skylights, I can have two unobstructed spaces 3 feet by 28 to 30 feet. With 8ft x 28” Panels we can house the equivalent of 2 full panels with 2x 2/5ths panels x 3 on one side and do 3 x 8ft x 20” down the other side only using 3 sheets. A fourth sheet will do us 8ft x 20” across the front and do 2x 8ft x 1ft panels leaving us short by 1 x 8ft x 1 ft to complete our array.

Here we organize the panels 5 per side 6ft x 3 ft each. But have chosen the configuration just discussed.

Wiring the array

We are not doing auto tilt so panel wiring becomes just 2 wires red and black going in parallel and passing to the controller.

Shown at the left is the wiring of the panels. The old fridge vent serves to pass the wiring into the coach and down into the main control center.

EV Motorhome Solar Charger system

    By eliminating the tilt operation we eliminate 4 GPIO expanders and the associated board and can handle everything from a simple board controlling all functions right from the RPI computer on the wall. The 57v Solar array is isolated from the 57v supply by a blocking diode so when the sun is not hitting the panels the panels can't draw from the Batteries. A contactor is enabled by the computer to control charging the batteries from solar so when the Batteries are fully charged the solar can't over charge them.

     This is the second solar system I am doing. The first was a 2 panel E-trike system for 24v. For the Motorhome the coach system handles shore charging and solar charging. References to a Mini-Van system was for a Mini-Van conversion which is basically the same for an EV Motorhome on a smaller scale.
    In all 3 renditions, the solar charge is a supplement to shore power charging. In the case of no shore power the solar system could be used. For those tied to Gas hogs or hybrid vehicles and even current fully electric vehicles, they don't have options if there is no charge station before their batteries die or fuel runs out.

    In a vehicle conversion scenario, the vehicle drive computer handles the charging rather than using two systems. Coming inside the Van we need a control center for the charge system that must handle 120v AC, @ 15A, and Solar charge. The Battery banks provide 384v with taps for 48v, and 12.6v. Our system therefore will need a Raspberry Pi and a monitor with touchscreen, an Automotive controller, and an inverter/converter/charger unit.

    This brings us to the last part of the plan. We must collect all the energy from the panels and get it down to the controller and subsequent battery banks. Point is that to minimize the wiring you want to have as few wires making a journey as possible. Because we are making the panels 57v we have already cut the wiring down to 2 wires. When the sun is poor or non-existent, a blocking diode in the controller prevents the battery from discharging through the panels which would destroy them.

    As seen the 14:2 cable comes from the solar array down to the coach system controller. The battery banks also feeds into the distribution panel near the controller. Our electronic processes use 3.3v, 5v, and our automotive systems for lights and fans and heaters need 12v and finally the Motor uses 384v. Typically speaking we need 3A for the 3.3v and 5v lines, and 10A for the 12v line. In the old 'ICE' design it used 12v @ 60A for the systems and 12v @ 600A to 800A for starting. The 384v line from the Battery goes to an inertia switch mounted to the frame then passes the 384v line to a Shunt resistor before traveling up to the engine compartment.

    Three wires also come from the shunt resister to the controller at the charge port. You can note that the heavier black wires are high current lines that pass outside the interior along the frame and the lighter / smaller black wires are low current that pass into the charge port controller.

Charge Port at old fuel door.

      Ideally, you want to minimize changes made or at least hide them. So in this case I will remove the gas filler along with the tank and put an interrupt switch with plug socket at the filler hole. The interrupter switch prevents drive away if the cable is still attached. It also enables the charge inverter to convert 120v AC @ 15A to 57v DC at 37A. The solar charge system provides 19A to 38A. Alone, it can charge the 288A battery in just shy of 62.25 hours. With solar charging it can replenish in 30.72 hours.

missing image of motorhome charge port

     Starting at the left, we have a 10 pin connector that feeds to the console computer. It provides Pol and interrupt signals and shutdwn and clr commands to a charge counter that is coulomb based. It also has +5v, GND, and charge enable lines. Below that is the 120v AC charge line that uses a microswitch at the charge port to indicate when the charge line is pluged in. The AC feeds a transformer and full bridge circuit to supply the charge. U2 is a 15A Triac controlled by the computer to enable charging. U1 is a coulomb counter chip that samples the voltage drop across a shunt resistor connected across two pads at the top. On the right are connectors for the Battery Packs, Main system line, and the solar charge panels. The Inertia switch (not shown) connects between the main line and the Motor Inverter circuit.

Dash computer - Charge control

     The coulomb counter sends one pulse each time .00017A pass across the shunt. It also gives a POL signal 0=Drain 1=charge so the computer can see how much battery use has been used or replenished. So as you drive, the computer starts with a full battery 703,080 ticks = 120A. Each time the coulomb counter gives a tick the full charge comes down by one. So if ticks left has reached 140,616 you have 20% charge remaining. You stop and connect to 120v AC and the computer sees the charging ticks and over a period of time sees it has now 140,616 ticks, it knows it has 20% and needs to continue changing. When it again reaches 703,080 it knows it is full and can stop charging. Because it can read charge from both solar and 120v AC it can see charging action from solar even when stopped during travel. The motor draws nothing unless moving.

     Solar charging is a method of charging Batteries using the power of the sun. While It can be designed to charge at any voltage, typically they are made for 48v systems and use a charge controller and can handle up to 4000 Ah given the right equipment. How effectively it charges is dependent on size of panels, number of panels, available sunlight and hours of sun exposure.

     Applications are also wide ranging. There are small panels ideal for portable use to charge small electronics like cell phones, PDA's, iPads, and Laptops. Larger panels can be used on vehicles to either keep a full charge on a battery such as Lead-acid, Ni-Cad, or Lithium ion Phosphate. Going with even larger arrays of cells you can do more than just charge maintenance. The Larger arrays may even replace the need for shore power on RV's, or work as a back-up system on brick and morter buildings.

     Each basic solar cell has a nominal voltage of 0.48v and depending on size of cell can deliver 0.5A to 1.96A, in the right conditions of sunlight. To charge batteries that are at a higher voltage, you would place several panels in series to achieve the desired voltage. To increase the charge current, for faster charging, you would connect them in parallel. In this manner, making an array of 5 panels in series by 5 panels in parallel you would get 2.5v at 10A (using the larger 52mm x 104mm cells). This would not be enough for a trickle charge of a lead acid 12v battery. 28 cells in series would be required to provide ~14v but in trueth 36 cells would give best results. Thats 180 cells to make a 10A 12v charger.

     The standard Photovoltiac cell is 156mm x 156mm (6" x 6"). The available cell sizes

• 39x26mm 0.5v .36A
• 52x52mm (2"x2") 0.5v .98A
• 52x104mm (2"x4") 0.5v 1.96A
• 52x156 (2"x6") 0.5v 3A
• 156x156mm (6"x6") 1v 3A

      An array to charge the 12v Battery with 36 cells would be 2016mm (80") long including the cell spacing and 4" wide. It could be configured as 2 rows of 40" or 4 rows of 20". At 2A it would take 30 hours to fully charge a dead 12v 60Ah lead acid battery. Given that the sun is up only 3 to 9 hours a day, it might take the array 3 to 10 days to fully charge the battery. This brings us to the next hurdle. What happens when the sun goes down? If you connected the battery directly to the solar cell for charging, the battery would discharge through the cell when there isn't enough light. This is bad for the cell and for the goal of having a charged battery. Using a diode, which conducts power in one direction only, we can prevent this discharge when the sun goes down.

     The charge controller is a device that is used to match the panels to the battery system and handle the charging operations. They are normally listed by wattage rather then by voltage and current. So for our 12v 60 Ah battery, we have 720w (12 x 60). The controller may do more than just prevent discharge when the sun goes down by configuring the panels (in watts) into a specific output voltage for charging and regulate the current coming from the battery or going into the battery. Often this includes overcharge and overdrain technologies. You don't want to keep charging once the battery is full or to continue draining from the battery once it is too low to supply power.

     Panels themselves, are premade of either monocrystaline or polycrystaline cells. monocrystaline do so in a much smaller panel than the polycrystaline ones and are more expensive. The Panels themselves are fairly thin but mounted to a heavier structure or frame to give it strength in adverse weather. For optimum efficiency you need to keep the panels clean from dirt and debris. Often you may find various adjustable mounts for aligning the panels to the best sun quality. Some controllers have the ability to change the angle and direction of the panels for highest sunlight transfer. Before moving on lets talk a bit about cost comparison. A monocrystaline cell can typically cost about $3.60ea. Comparing to polycrystaline the cost per cell is $0.13ea.

Now lets make it happen

     Let us look at our motorhome. It has a 384v 288Ah battery system that we want to charge from a 48v solar. To do this we need to either multiply 48v by 8 to get to 384v which involves a transformer and considerable power losses or we can convert the 8 series 48v blocks into 8 parallel blocks for charging and switch them back to series for running. Method one (transformer) is huge at 10" x 6" x 8" and due to losses is less than 65% efficient. The unit will typically cost over $150. Going with a switching method, we can use 6 Mosfets at each of 8 x 48v Gcells. Costs come down to $64 or less, weight comes down from 10 lbs to 2.4 lbs, and size comes down to 0 since we use spare space at each 48v block to put the Mosfets. The second method serves both 120v AC charge and our solar charge at the same time.

     With our charge delivery plan worked out and knowing the solar source voltage is to be 57v it is now a matter of cell arrangement to achieve the voltage and as high a current as space permits. Because our Blocks are 48v, we need 57v to accomplish charging. Polychrystline cells are 0.48v so 119 cells are needed in series.

The following is for a motorhome for other conversions the figures need to be reworked.

 Step 1: We need 19 box frames 4ft x 20" made from 5/8ths 'U' channel and with a mounted plywood base 1/2" thick. On the plywood surfaces we need to mark out 2.125 x 4.125 squares into rows and columns observing there must be a 0.5" border around the edges and room at either end for wiring bussbars.

Custom solar Panels

     Basically you have UV protected Plexiglass about 1/16th to 1/8th" thick covering a 1.3mm thick fragile solar cell and backed by a rigid backing that may be 1/8th to 1/2" thick sealed in an environment tight frame.

     Dirt, grime, and moisture are the main culprits to the demise of panels from an environment standpoint. This is especially true when making the panels. From the in use perspective, you want a strong construction that is light in weight and not prone to bending. You must never let anything especially fingers touch the surface of the cells. USE NON-COATED INSPECTION GLOVES when handling these cells. They are fragile and easy to break. A well made panel has a life expectancy of 15 years. So lets look at what you need.

1. 1/8th" Thick UV Plexiglass 48" x 96"
2. (5) 4'x8' x 1/2" Plywood
3. Silicon clear caulking
4. (833) 4" x 2" polycrystaline Solar cells
5. 1 spool tapping wire
6. 1 spool bussing wire
7. 1 spools Red 20ga wire
8. 1 spools Blk 20ga wire
9. (6) 5/8" x 1/2" 'U' channel 6.5'
10. (6) 5/8" x 1/2" 'U' channel 30"
11. (2) 5/8" x 1/2" 'U' channel 6.5'
12. (2) 5/8" x 1/2" 'U' channel 17.5"

1. Lexan cutter
2. 3 ft ruler
3. speed square
4. Drill & bits
5. Flux pen or solder paste
6. 60/40 solder
7. wire stripper / cutters
8. 60 watt soldering iron
9. Marker pen
10. Multimeter

Down to Business

    We are going with a sealed aluminum frame design.

     Before we get started assembling cells lets actually plan out our frames and get things aligned right. First off, we need 2x 48" U channel mitred at 45 degrees. We also need 2x 20" U channel mitred at 45 degrees. These will make the out side frames edges. Take your Plywood and cut fit snug inside the frame edges. The edges of the 1/2" plywood will have a 1/16" x 1/2" rim around the edge and the 1/16th inch Plexiglass lens to fill out the space. You can secure the 1/16th inch plexi to the plywood and fasten the plywood to 3 of the frame edges from the underside. Seal the mitred edges with rubber cement. Using the lexan tool you can score the Plexiglass and make a clean break.
    First Dry fit: With our backings all ready we should be able to place the Clear plexiglass onto the frame and fit the 'U' channel over them for a very tight fit.
     Our custom array will mount to the roof. 14:2 electrical wire will pass from our panel through the roof at the back and down one side of the rear van frame. Now we need to turn attention to the wiring and the cell placement plans. Find yourself some construction paper large enough to make two templates. One template will be 48" x 20" and the other is 4.125" x 2.125".

Wiring path

      We are going to have 5 columns x 24 cells on each 4 ft x 20” panel. By inverting every 2^nd row we get + - + - + at the top with 57v – connected + and minus connected to +. along the bottom we get – connected to +, - connected to + and GND. All panels have the +57v connected together and all the GND connected together. We have two wires 57v+ and GND passing to the controller.

     So here is the plan, if we align the panel such that power is handled at the rear of the vehicle Top will actually be towards the rear. This will make it easy to run wiring down the rear frame post.

Left is the diagram of a 5 bank system used on my tricycle. Panels stacked over each other to keep them safe when not in use.

Wiring up the cell Banks

      Gloves on!, make sure your area is clean and open the package of 900 cells. Grab your multimeter, A piece of copper PCB and some wood to make a little stand. We will want to take a piece of plywood about 5" square and place a small 1"x2" by 5" along one edge and 2"x2"x5" piece of wood along the other edge of the wood square. Then place a copper shiny side up angled between the two pieces of wood block. As we check the cells we will lay the dull side against the copper such that the positive cell contacts the copper. In this way we can check the voltage and amps of each cell easily.
     The cells will have 6 positive contacts on the dull side and two negative strips down the blueish face. If you bought tabbed cells each cell will have tap wire soldered to the facing. If you bought plain cells you will need to solder tap wire to the facing. But for now, just place the cells one at a time face up on your jig and measure with positive on the copper and negative on the face strips looking for .48v and again for 1 to 2 amps depending on sunlight.

Tap stripping the cells.

     For each cell pair we need the tap wire to cover the negative strips on the face and connect to the underside positive contacts. The tab wire does not need to pass past the end of the next cell. So 2" is all you need given that each must be spaced 1/8" apart. If you bought tabbed solar panels you only need to trim the tab wires to 2".

     After you have got your work area setup, and tab wires cut to about 4.125" you are ready to start soldering. The soldering iron I use is adjustable from 10-100 watts, I have it set for 40 watts. Be sure that your iron tip is clean and tinned properly, as you work keep cleaning the tip because a dirty tip will possibly contaminate the process.

     You see in the picture there are white stripes from top to bottom. These are where you will attach your tabbing wires. The tab wire is not completely at the top of the solar cell. This is just to be sure it does not contact the cell that will be above it.

1. First you need to use the flux pen. put a light coating of flux on that white stripe. You see the darker blue areas, that is flux that flowed off the white stripe.
2. Lay your tab wire on this stripe.
3. Using a soldering point tool (or something similar) to hold the tab wire in place. don't press to hard, you might crack the solar cell under the tab wire.
4. Moving from top to bottom, use your soldering iron and start soldering the tab wire down. Don't let your iron sit in one place to long, you will burn the solar cell. You will need to move your holding tool around as you move the iron down, don't let the tab wire move. Hold the tab wire down until the solder cools.
5. Repeat for all tab wires on each cell.

Cell inter-connections

   As you have enough cells tabbed to do 5 columns (119 cells) we need to interconnect them one row at a time. Remember the blue face is negative and the back is positive. The back may have either 3 contact spots in two rows or 2 partial strips.

1. Flip over all the cells that need to be connected, and put flux on the white areas.
2. Lay the tab wires from the top cell onto the back of the bottom cell. All cells need to connected front of one cell, to the back of the next. This puts them in series. And keep the cells 1/8th inch apart and tab wires must not extend past or even close to the ending edge.
3. Solder the connections.
4. Repeat until you have all connected.

These cells need to be connected in series because each cell produces 1/2 a volt DC. We are making a 57v panel so we need to tie them in series. This is a "no load" reading. When these cells are put under a load, such as charging a battery, the voltage should drop a bit. When all series string are connected, we should see 57 volts.

Connecting cell Rows

    We are making 1 panel with 119 cells in series. Now I will show how to connect the columns.
As I stated before, cells need to be connected front side to back side. On the end of the string you need the 2mm tab wires protruding from the ends of the 2 strings you need to join. You can use shorter tab wires for this if you want to.

1. Add tab wires as needed to the end of the strings.
2. Lay the strings next to each other with a small space in between them. I would recommend doing this on the glass you will be using for the solar panel, or on something that these cells can be kept on until they are ready to be put into a panel.
3. Measure out the length you need for the buss wire. Then cut the 5mm buss wire to your measurement.
4. Use the flux pen on the places that the buss will be attached. You only need to put flux on the tab wires, not both tab and buss wires.
5. Line up your buss wire on one end of the tab wires. The buss wire does not need to stick out over the end, just make it even. Keep it close to the cells, but do not touch them.
6. Work your way from the first one you soldered, keep the buss wire flat as you move.
7. After you finish soldering, cut off any of the wire sticking out past the ends of the tab wires and the buss wire.

   In the picture where the extra wire has been trimmed off you see an extra tab wire on the left string. I put that tab wire on there to test the cells to be sure they were connected. I stated earlier that cells produce 1/2 a volt, so 4 cells should be 2 volts. I was sitting under a incadescent light when I tested these cells. I got a reading of 1.4 volts. That is very good since most cells will not work unless they are exposed to real sunlight.
Remember when testing and connecting the wires that will run out of the panel the top side of the cell is negative, and the bottom is positive.

End of strings

    In addition to connecting strings you will also need to put a buss wire on each end of your cells (cell 1, and 39). This is done in the same way as connecting 2 strings, but you are only connecting the 2 tab wires on that one end cell (1). But on other end you are connecting all 4 wires to the buss wire. I leave a little extra hanging over on the ones on the top. I do this so that when I add a copper wire that will run out of the panel I can fold the buss wire over the copper wire and solder it together, making a stronger joint.

The buss wire can be done before or after connecting strings, that is up to you.

Panel assembly

     With luck you have 5 strings made in series with 1/8" spacing between each cell and each row. At one end you have two buss bars and at the other you have one long buss bar. So now take your template and transfer the markings for the bottom to the plexiglass (frame is taken apart for this). I would put a center hole through the template for each of the cells and then mark the back plate where we need to put a drop of silcon sealant. remove the template and apply the sealant. Now carefully position panels observing that you place them the right direction with the double buss bar at the top. You might want to also put sealant under the bottom buss bar. DO NOT PRESS TOO HARD on the panels or they will break.
     Apply silicon sealant to the U channel (one with the wiring holes) and place the frame piece into position. Use a 1/8th piece to simulate the lens for now. Feed a Red wire through one of the holes and extend it across to the left buss bar at the top. Strip and solder the Red wire to the buss bar. Next Feed a Black wire to the other buss bar and strip and solder it. These red and Black wires come out of each panel to be wired to the next panels red and black wires. Apply silicon sealant to the hole inside and out to seal it from moisture.
     With this done you can now assemble the top and bottom parts of the frame using silicon and the 1/8th" spacers. Remember to also put silicon sealant on the ends of the frame too. Flip the frame over and using a small pilot hole drill 1/2" mounting holes around the frame and put in 1/2" #6 roberts screws to secure the frame pieces. Lastly slide the lens (with protective cover removed) into the frame from the open edge. Silicon and install the final U channel and drill and screw it from below. Now seal around the Plexiglass where it meats the frame. 1 Panel Done!

Charge / Discharge Control

Battery capacity

     The amount of charge that can be delivered into or out of a battery, is important in the determination of available charge for use. We can measure voltage and get a very basic determination because the voltage will drop as the charge is depleted. We can measure the current being taken from or put back into the battery but it really doesn't tell us the total capacity full and how much is left. A coulomb is in the unit of 1 Ampere-second. Another way to put it is the amount of Amperes that can pass a certain point in 1 second. Because there are 3600 seconds in an hour, one amp hour equals 3600 coulombs:
1Ah = 3600C

Measurement by Voltage

     We have this 3.2v Lithium cell during charge we can charge it at a maximum voltage of 4.2v at the risk of shortening it's cell life. We can also reduce the charge voltage to 4v and take longer to charge the cell which is safer. Once fully charged and the cell has had time to rest we can measure the voltage and see about 3.2v on a good cell. If we keep monitoring the voltage and start using the cell to power something, we will see the voltage drop and can stop the cell from further discharge when the voltage reaches 0.62v. At a steady current draw, The cell will deplete faster as the voltage drops. So you can see this method is great for the cell when it's only going to be depleted near the top. So if our 48v Battery is fully charged it shows slightly more than 48v and can deliver full current until it reaches about 75% then it starts a slow decline in volts to say 45.2v. It is still delivering the current (amps) but now starts to decline faster and by 50% is now reading 37v. A even shorter time later it is at 15% and well below 20v. To you the operator with just a voltage gauge to go by you traveled 25 miles in 15 minutes showing voltage above 45.2v. The next 15 miles you got down to 36v, and then you went another 6 miles and your battery is almost history.

Measure by Current

     Years ago, automakers made the decision to stop putting analog current meters in cars because of the huge risk of electrocution by passing 60+ Amps into the dash where occupants are. This was for the time the best way to determine battery health. It allowed an operator to read the draw of current going into or out of the battery such that if the meter said discharge 12A you knew you were at that time using 12A of power. If it said charging 12A you were refilling the battery with charge at 12A. Your biochemical computer (Brain) could kind of calculate based upon voltage and drain how far you could travel. But once more it didn't really tell you how much charge was in the battery. You know it's not like a clear water tank where you can look and see how full it is. Today, we use shunts to make measurements like this safely.
   With a shunt, a very small value of resistance is placed inline with the power wires and we measure how much the voltage drop is across the resistance. Because the voltage being measured is so low and the current through the resistance is also low it is safe. We can now measure the current entering or leaving the battery. We still don't have a way to see the level of charge in the battery. We can see fluid levels but those darn electrons are too hard to see.

We just can't see electrons

     It's like they are sub-atomic. Oh my gosh that's right they are! So if we set up a clear barrel and call that a battery. Attach a hose and call that our power wire. Put water into that hose and call that our voltage. And then depending on how fast we fill the barrel (pressure) and call that our current. We can visually see when the barrel is full. If we put a water meter inline with the hose we can measure the amount of liquid that has gone into the barrel. Then when we start taking water(voltage) under pressure (current) out of the barrel, we can again count backwards using the meter to know when it is empty.
   Based on the full reading and the empty reading we can tell how full or empty the barrel is. That in a nut shell is the problem at hand. We need to count charge going in until full and count charge coming out until empty simply because we can't see how much is in the barrel (battery).

Measure by Coulombs

     We are going to investigate how the LTC4150 Measure's Coulombs.

     The LTC4150 is the electrical equivalent to the liquid flow counter of the last paragraph. The LTC4150 has an output pin called interrupt, or INT for short (the line above the name indicates that this is an "active low" signal). This line is normally high, but will pulse low each time 0.614 coulombs passes through the device (which also happens to equal 0.1707 milliamp-hours or 0.0001707 amp-hours):

1 INT = 0.614439C
1 INT = 0.1707mAh
1 INT = 0.0001707Ah

Or to look at it another way, you will get 5859 INT "ticks" for each amp-hour:
5859 INTs = 1Ah

Keeping Track of the Charge in a Battery

     As you know, battery capacity is measured in mAh (milliamp-hours) or Ah (amp-hours). If your battery holds 1 amp-hour when it's full, you can continuously draw one amp from it for one hour before it's empty. You could also pull 1/2 amp for two hours, or 2 amps for 1/2 hour, etc.

     Using our favorite tool the computer we can enter the maximum capacity of the Battery pack in Ah (Amp-hours). We can then monitor the ticks and direction from the device to add or subtract from the full capacity. Compute the two values in real time to inform us how full the battery is. It has more implications than that too. When charging the value can tell us when to absolutely stop charging so as not to overcharge the battery. It can also tell us when we can't go any further without damaging the battery.

     Because it measures amp-hours as you're using them, the coulomb counter makes it very easy to keep track of your battery's state-of-charge (how full it is):
     To use a coulomb counter you need to use it with a computer and the people at sparkfun have developed a circuit board for just this purpose that can be used with the Raspberry Pi computer, Ardunino controller and other such devices.

     First, assuming you're starting with a full battery, set a variable to your battery's initial state-of-charge (e.g. 1000.0 mAh).
     Listen for the "tick" (low) signals from the INT pin. Each time you detect a tick, check the direction signal, and add or subtract the above per-tick mAh value (0.1707 mAh) to your battery-state variable.

Head on over to https://www.sparkfun.com/products/12052 for a complete run down on the use of the coulomb counter and sample code for the Arunino type controlers.

     For battery sizes greater than 1 Ah you would adjust the number of ticks to # of Ah * 5859 ticks. So 2Ah = 11718, 20Ah = 117180 ticks and so forth.

* Note that in real life it takes a bit more current to charge a battery than you'll later get out of it. This is because the chemical processes that store charge aren't 100% efficient, with the excess turning into heat. The amount of loss varies depending on the type of battery, charge rate, age of the battery, temperature, etc. You can account for this by providing a manual "reset" input when the battery is fully charged, or doing some calibration to see how many more ticks you get when charging vs. discharging (though this will change with battery age, temperature, etc.).

Bonus: Determining Average Current
An additional (and entirely optional) trick is that if you keep track of the time delay between "ticks", you can back out the average current used over that period. The equation is very simple: mA = 614.4 / (delay between "ticks" in seconds)

Note that because this number is the average current use over the time period, the instantaneous current could be higher or lower. This is also covered in their example code.

Connecting the Hardware

     The LTC4150 Coulomb Counter IC has a very simple interface. It has an INT (interrupt) output that is normally high, but will go low when a given amount of current has passed through the device. There is also a POL output that tells you which direction current is flowing.
Max Ratings:
     The Coulomb Counter can accommodate power sources up to 8.5V, and currents up to 1A. It works particularly well for single-cell (3.7V) Lipo batteries, LiFepo4 (3.2v) up to 1000mAh.

     So on their site, they explain the straight forward way to connect this handy device to the Arduino using it to power the board (IN & GND) and the passing of signals from the counter (/int & POL) and from the controler (/Clr & /ShtDn)
     Under this scheme, The battery source goes to the input (IN) and the load connects to (OUT). If using a charger as well to count both charge and discharge the charger goes on the (OUT) side.

But my Pack is 12v @ 20Ah or 48v @ 100Ah

   Traces on the board and the LTC4150 can't handle more than 8.5v and / or 1.6A so what can I do now? They say there is no easy way to handle higher values more easily, but, and there is always a but, it can be done. But first lets talk about Interrupt vs Polling. Using interrupts is fast and assures the most accurate counts where as Polling means you check it at intervals and hope not to miss counts. To poll the device you need to open the SJ1 connection so that if an int occurs it stays low until the CLR is pulsed low. If your code is too slow to react you will miss counts under polling.

By default, the Coulomb Counter is set up so that the INT output will go low and immediately return high. It will only be low for a few microseconds (millionths of a second!), which is enough for interrupt-based code to detect the falling edge, but random checking will almost certainly miss such a brief signal.

Wiring the Hardware

Here are the minimum required connections for the example sketches.
If you want to try the interrupt example code:
Leave solder jumper SJ1 closed (the default) You will need to connect (at least):

• VIO to VCC
• INT to D3
• POL to D4
• GND to GND

If you want to try the polling example code:
Open (clear) solder jumper SJ1 (Instructions)
You will need to connect (at least):

• VIO to VCC
• INT to D3
• POL to D4
• GND to GND
• CLR to D6

For EITHER version of the code:
Ensure that SJ2 and SJ3 are both open (clear) for a 5V Arduino, or both closed (soldered) for a 3.3V Arduino.

Downloading the code

     The example code is maintained at the Coulomb Counter BOB Github repository. You can download a ZIP file of the entire repository (or clone it to your computer if you have the github software installed), or save the sketches directly.

Changing the Sense Resistor

     The Coulomb Counter uses a sense resistor to measure current. This very small resistor (0.05 ohms) is the only component located between the input and the output. The LTC4150 measures the voltage drop across this resistor; thanks to Ohm's law the voltage drop is directly proportional to the current passing through the resistor. This resistor is known as a shunt. Just like automotive ammeters of years ago, shunts were used to govern very high battery currents to display on very low current meter movements. And this shunt gives us a new way to use the LTC4150

In real life applications you can go with a 0.0002 ohm shunt to achieve 250A in 5859 ticks which means 1 tick for each .042A. But this is untested by me.

    Using ohms law you can determine what current flow is through the measurement of the voltage drop across the resistor. As such, if 1v is dropped across a resistor of a value of .05 ohms the current through that resistor is 1/.05 = 20A, changing the resistor to .0002 ohms would drop the voltage under the same 20A load to only .004v. This is why lowering the value of the shunt resistor works with the current PCB.
* Note that the PCB traces on the board are not designed to handle more than 1.6A continuously, and the JST connectors are not designed for more than 2A.

     They state there is no easy way to increase the maximum supply voltage above 8.5v and this is partially true. Typically you make measurements from supply to ground return. This is 8.5v maximum in this case. But if we employ level datum shifting we can accomplish the same thing. Suppose we have a 384v dc Battery in an EV and we want to count the coulombs with a potential draw of 250Amps. Obviously this little board would get fried if you tried. But get this, a 5V zener diode #NZX5V1B_133 in series with a 75k ohm resistor raises the datum such that the board sees only 5v and the board is happy. It has no idea that the 5v is being taken from the 379v(symbolic gnd) and the 384v supply. Now using a opto isolators device that is suitable for mismatched voltages and currents we can relay the ticks from our 384v system safely through optics to our 5v computer system. We can also control the device the other way. The 75 ohm resistor in this case would need to be a 20watt because of the current and voltage it is having to dissipate. The preliminary layout shown later does not take this into account. To handle this situation the high wattage heat generating resistor would need to be mounted off board.

   As can be seen here the ilq2 quad opto isolator has 4 distinct units in one 16 pin dip package. on the photo diode side we just need to place a bias resistor to either the plus or negative rail and supply our signal to control active high or low accordingly. This would be supplied by the int pulse. The microcontrol side has a similar bias to it's much lower voltage source and receives the int signal to the microcontroller. The same is true for the pol signal it senses the direction of current and tells the diode to go high or low and the Phototransistor side tells the microcontroller what the result is. For the other two signals we need to go the other way. On the computer side we use the same biasing as we did before and supply the CLR and SHDN signals to the diode and with same precision pass that information onto the high voltage side using the Phototransistors to relay the results to the board. Resistors 2 thru 9 are selected to sink 5ma so to meet with device specs they are all 750 ohms 1/4w. And here we have the daughter board that accomplishes the task with ease.

   In the above we have not removed the on-board shunt yet. The blue wires patch our off board heavy shunt resistor onto the Coulomb Counter. The boards interconnect with ease.

   An understanding of the ilq2 IC. Shown is the chip layout and the represented circuit. Both the diode side and the phototransistor side have resistors pulling the inputs high. They also have cathode (diode) and emitter tie to ground tags. BUT these positive rails and negative rails are NOT the same. On the computer side the plus 5v and ground are that of the computer. On the high voltage side, Plus 5v is actually 384v and ground is a SYMBOLIC ground 5v lower than the 384v. R1 determines the voltage drop value and current supply at 379v @ 50mA. The Zener diode assures the potential difference is 5v at all times.

    The board is simple having 1 Zener diode, 9 resistors, and a ilq2 quad opto coupler IC. Besides the connections made from the coulomb board to the daughter board, we have just 5 wire pads to connect the external Shunt to the coulomb counter and our computer connects to the 6 pads of the new board instead of the coulomb board. Problem solved.

     As designed the daughter board add-on can work with up to 500v and depending on the shunt resistor up to 600 Amps. Because we are Level shifting from the high voltage supply, The board can be used for any voltage from 10v to 500v. The LTC4150 will always see 5v as it's supply. R1 is sinking 379v @ 50ma so it's value is 7.58k. If you supply only 10v as a supply this would reduce current to only 65ua so the value picked would need to be smaller, like about 100 ohms. The shunt resistor on the coulomb counter board must be removed if doing high voltage. The shunt resistor you will be adding to the daughter board high voltage contacts must be selected such that for 384v a shunt of .0002 ohms will produce a voltage drop across it 50mv and a current of 250A. The shunt resistor would be a maximum of 30w

     From the original published specs of the Coulomb Counter They are saying it can count 1A based upon the 0.05 ohm shunt. This addresses that the coulomb board is measuring a voltage drop of 50mv. This modificaton means that instead of getting 1 tick every .0001707 Amperes you will see 1 tick every .04 Amperes which for a high current supply under high demand is still quite useful.
Side note for those who are worried about close proximity of 384v to 5v this a real non-issue. We are taping 50ma from the 384v Battery pack and due to the Zener we are using 5v for control on both sides even though the 5v potential on the high voltage side is taken from the top of the 384v rail. the device is rated for 10 mA with isolation up to 4Kv. That isolation is almost 1000 times what we may see in the worst case.

Special note here. When you start to move there is a half cycle surge up to 25 times the motor current draw. The motor maximum run current is 10A but during initial start it can have a 200A spike for about 0.00833 seconds. That is why we planned in for 250A. The slower you start to move the less surge you get which can extend your range substancially. Once the vehicle is in motion you can apply more acceleration.

Using the SHDN Input

     You can reset or shut down the LTC4150 by making the SHDN input LOW. This will reduce the power consumption of the board, but the LTC4150 will not measure current consumption in this mode. This input has a pullup resistor; if you do not need shutdown functionality, you can leave this input disconnected. Refer to the LTC4150 datasheet for information on resistor selection. There is also a spreadsheet in the Github documentation folder that may be useful.

Use in an EV Motorhome

     The Battery banks for the motorhome will be 384v @ 84Ah minimum. The datum resistance needed must drop 50mA @ (384v-5v=379v). The resistance value is 7.58K ohms @ 20watts. For the shunt, we know that 5859 ticks = 1A because each tick is .0001707A using the original design. Our Pack voltage is 384v with capacity of 168A. Under charge it is getting 37A and under discharge it is drained by up to 10A with surge of 200A. We can't use the original design specs of .05 ohms because at surge time that would result in 7.5v which is 150 times the maximum potential of the chip. The shunt must be reduced in value. 0.05v / 250A surge = .004 ohms. We also need to control 3 related systems while tracking the charge and discharge. As such we made a special charge control for our motorhome.

EV Charger

     The charge controller takes direction from the coach computer and the AC charge port. The computer provides 4 enables (battery pack 1, battery pack 2, Solar, and AC charge). At the AC charge port there is a microswitch that is activated by inserting the plug into the port. When AC shore power is plugged in, it converts 120v AC to 60v AC and if the computer has issued a 'charge-enable' signal passes that AC voltage on to a full wave bridge rectifier to produce 57v DC for charging. As long as the AC charge cable is plugged in normal vehicle operation is prohibited. The 57v used for charging has 37A of charge current. As it passes through the coulomb count circuit, we have .00034 ohm x 37A = 10mV and since the coulomb counter is measuring the voltage drop in mV it can adjust the ticks to match.
     Roof top solar panels supply power when there is sufficient sunlight also to the charging system. It can also be enabled/disabled from the computer. When solar charging the counter again is measuring charge in mV from the drop across the shunt. The 2 battery pack enables determine which battery pack(s) to use. Each has a contactor run by the enables. During drain to run the vehicle, a second coulomb counter notes the direction change of the charge to be discharge and counts ticks of current going the other way.
     The limits of the 120v shore power is 15A at source to provide 37A at the Battery packs for charging. The solar array provides 10A or more. The size of the battery Packs and their current state of charge governs how long charging is going to take. Taking the case of a 300Ah pack and 30A shore charge, it will take just over 10 hours from empty. Using shore and solar would reduce charging to 7.5 hours. But, and there is always a but, You can't discharge the Battery Packs less than 20% or they will be damaged. They also can't be charged to more than 98% so full charging range is 234A or 7.8 hours using AC shore power. Using both shore and solar cuts charge time cuts to 5.8 hours. If we do as planned to use 2 packs of 144Ah for charge times which will be longer. One last contingency is the solar charge while parked between trips. During time you are parked or stopped, the solar can charge at 10Ah while you dine, shop, or work at a job. So assuming you drove to work and used 120Ah from the packs and solar charged for 8 hours while at work, you effectively only used 40Ah. When you get home total use was 160Ah so your charge time becomes 5.3 hours on shore power. Costs at 0.15 per kw means it is costing 0.27 per hour for charging. 7.8 hours to charge to full is $2.10, 5.3 hours is $1.43. A substancial difference from $20 to $40 a day for gas.

    All connections to the charge controller are on one edge. A 10 wire connection goes from the controller to the dash computer distribution pcb. A microswitch at the charge door connects next followed by the 3 wire AC 120v connection. The power wires from the roof top solar array connects next. Then we have the 48v power to the automotive function board and two sets of Battery pack connection. There are two off board parts. A terzoid transformer is one and the Shunt Resistor is the other. The shunt resistor is due to size and heat it produces and the transformer is just due to size.

EV Battery 101

Choice of cell types

     Batteries lie as the source of energy to power the EV. The type and configuration of the Batteries determine the potential of project design. Below are the specs for the four common lithium cell types. While all four can be combined to make the Banks or packs, the cell size and availability are the determining factors to project success.

   From our the chapter on the chassis and Battery specs we know we have 1844 lbs to 2198 lbs for battery Pack. We want 2 Banks to a Pack and 8 Gcells per bank. The Gcells will contain 15 cells in series and 7, 14, or 24 cells in parallel to give us 42A, 84A or 144A Gcells. Having just 3 Gcell types 48v x 42A, 84A, 144A gives us 10” x 10” x 6” , 10” x 10” x 12” and 10” x 30” x 6” sizes suitable for any size of vehicle. Gcell weights of 34 lbs, 68 lbs or 115 lbs. All using 32700 cells. So read on to see how I worked this out.

     In this chapter the term cell or battery refers to the individual cells like items 1,2 and 4. Gcells will refer to the 3rd type below as a Gcell that is really a group of type 1,2, or 4 arranged into a single larger device. A Bank is a group of Gcells and a Pack is a group of Banks. In my design of battery packs I always have 2 interchangeable banks. An MBank is where multiple banks of Gcells are connected in parallel to take the place of a single bank such where we might have a 42A bank and 2 banks per pack for a total of 84A we can instead wire 2 banks together as an Mbank thereby effectively doubling the pack to 168A and have just 2 mbanks.

The 18650 was the original cell of choice for EV at 18mm x 65mm providing 800 to 1500mah. $5 to $12 The 21750 is the new choice at 21mm x 75mm with 5000mah $16 The 32750 is my preference 32mm x 75mm at 6000mah. $10 is the cheapest cost of the 3 and although it is bigger and heavier, when your talking about 1000’s of cells to make a pack the cost savings are significant. Consider this: To make a 384v 144A bank with 2 banks to a pack we need 120 rows in series by 144/cell Amps in parallel per bank with banks then placed in parallel. 18650 cells = 2 x (120 x 96) = 23,040 cells $276,480 2142 lbs 21750 cells = 2 x (120 x 29) = 6912 cells $110,592 691 lbs 32750 cells = 2 x (120 x 24) = 5760 cells $57,600 1843 lbs

   So in the above we are targeting 384v @ 288Ah. If we run 8 Gcells in series we get the 120 cell value making 384v. Each Gcell has 15 cells in series and a different quantity in parallel such that the Gcells vary in size weight and price. Gcell Length is 5.6” for 1), 8.4” for 2) and 10” for 3). Gcell width is 4mm smaller for 1) than 2) or 3) but height becomes 67” for 1), 26” for 2) and 30” for 3) and you saw what happens to weight and price.
Factors to consider in converting a vehicle into an EV is really weight vs cost vs range in miles. We will remove:

1. Gas tank sizes vary so we will just use 80gal so fuel weight is 500 lbs + tank at 35 lbs
2. engine 735 lbs
3. transmission 135 lbs.
4. exhaust system 85 lbs
5. 5 x lead acid battery 425 lbs.
6. fresh/waste water 500lbs
7. doghouse 60 lbs
8. Hot water tank on propane 60lbs
9. about 10 lbs of dash equipment like instrument cluster, & radio.

   So when we convert a vehicle we are reducing curb weight by ~2535 lbs. Then we add back the motor, inverter, and digital control center 140 lbs. So we are ~2395 lbs lighter in curb weight at this point. If we use 21700 type cells a 145A Bank is 3480 cells for $55,680 and 313 lbs.
Using 32700 cells is a 144A Bank with 2880 cells for $28,800 and 921 lbs.
The number of cells and cost per Pack is drastically reduced and still leaves us with-in the weight margin. That is why I chose to use 32700 cells for the off the shelf Gcell Batteries for all converted to EV vehicles. And if the auto manufactures would adopt this same concept all vehicles would be more friendly on the pocket book.

   Curb weight does not include driver, passengers, cargo on cars and trucks so we can’t use curb weight to define range. On a motorhome as outlined here, GVWR is listed at 17500 lbs. So this tells us the maximum weight and we can figure that since a motorhome is our home it has all our belongings. So we deduct GVWR-Removed items= available for additions = 2395 lbs. Miles of travel is = Kw/(GVWR/10,000) with Kw = V x A so with 384V x 288A = 110.592Kw. Total distance in miles = 110.6/1.75 = 62.8 5 miles (104km) between charges. If we pull a car behind us the distance of travel = 110.6/2.40 = 47.04 miles 76.74km). As long as we are just traveling Alberta where campgrounds are 70km apart we can hop from campground to campground stopping over long enough to recharge before making another jump.

Recharge times per bank (1152A/8 Gcells per bank = 144A) *not all campgrounds charge for power

1. 15A shore power = 1152A/37A=31.5 hours $0 to $25.57 @ 0.17 per kwh
2. 30A shore power = 1152A/74A=15.75 hours $0 to $25.57 @ 0.17 per kwh
3. Solar charge = 1152A/19A=7.5 days because sun is out maybe 8 hours a day $0

   Because we have 2 banks the charge times double. Once charged back up (2 to 3 days) we can stay and camp there or make our next campground jump. Although we are 285 lbs over weight our chassis spec on the GVWR includes 500 lbs of fresh water, waste water so if we dump all tanks before moving we are under weight by 215 lbs. Adding 19 x 1A to 2A solar panels 180sqft at 2.5 lbs/sqft=450lbs. So our maxed out Motorhome with 76km range will be 17285 lbs without solar and 17735 lbs with solar. The GCWR remains at 24,500 lbs. We can pull a trailer with car on it if under 6265 lbs or a four wheel down car 6265 lbs. But when all is said and done we have few options.

   For EV to work we need replaceable Gcells 48v @ 42A for cars and trucks, 48v @ 84A to 144A for larger vehicles like motorhomes. The Gcells would be 34 lbs or 68 lbs or 115 lbs each respectively with size of 10” x 10” x 6” to 10” x 10” x 12”. 8 Gcells per bank and 2 banks or more per pack.

   Our proposed battery packs for cars mini-vans and suv’s for commuters would be 2 banks of 8 Gcells, Each Gcell would be 15 series rows x 7 cells in parallel. Each Gcell would be 48v @ 42Ah and Gcell weight would be about 34 lbs and cost $1050.00 . Range between charges would be 70 miles with 4 hours charge time per day if driven 32 miles a day. Charging costs $2.39 a day compared to ICE at $6.07 a day if 30mpg. Savings over 15 years $20,148 - $16,800 for new batteries = $3,348.00 for vacation! (does not include interest on savings).

   People needing higher ranges could pair up banks in parallel such that banks become 2 banks of 2 mbanks (4 banks wired with 2 connected together as one).

1. 32750 cells = 4 x (120 x 7) = 3360 cells $33,600 1074 lbs range 140 miles

2. 32750 cells = 6 x (120 x 7) = 5040 cells $50,400 1611 lbs range 210 miles

   The problem of doing this is that the weight is too much for small cars and mini-vans. MIdsize cars and light trucks might be able to handle 1) above, but only full size cars and ¾ ton Trucks or larger can do 2) above.

   Remember that the auto industry wrongly specifies GVWR by curb weight which excludes passengers and cargo. The mini-van curb weight was 3460 but had a GVWR of 4430. The GCWR of the mini-van allowed for a trailer of 3000 lbs so technically, because it’s GCWR listed at 7400 lbs we could attach a 3000 lb trailer with capacity for 2100 lbs and use 537 lbs of that to add additional battery banks. Thusly, bank-A now has the onboard bank and the satellite bank-A in parallel and doubles Amps to 80A. Bank-B now does the same and our range almost doubles during run. Our GCWR now comes into play. With GVWR of 4430 + 3000 for the trailer we are now at 7430 GCWR we have now got 61.44Kw so 61.44/0.743 = 82 miles instead of 70 miles if the trailer is full. We gained more range by adding battery banks but lost range because cargo space increased by 1600 lbs or more. If the trailer costs $1,400 and battery banks cost $16,000 our range increase of 10 miles cost us $17,400. On the other hand, if the trailer only has the battery banks, GCWR is 5867 and 61.44/0.5837 = 104.72 miles.

Battery Pack health

   Cells decline and fail at different rates. As cells in use go through life they start taking less charge as they age. In a one pack does all this can mean that if rate of decline results in say 10% of original distance the answer is to replace the whole pack for $16,800 for example. But because we are using Banks, If only 1 bank has declined rapidly, we can replace the bank $8,400. Our banks are 8 Gcells that are individually replaceable so narrowing it down to a Gcell now results in $1050 as cost of repair. The user can now replace their own battery Gcells just like we do when our lead acid wet cells need replacing. An $85 wet cell is 80 lbs and sits on store shelves. With standardization we can have stores stock our 34 lb Lithium cells on the shelves for $1050 each. Environmentally, we are moving away from harmful lead acid in favor of recyclable lithium ion.

   Just like with lead acid where we turn in the battery for core charge so it can be rebuilt, the gcells can be rebuilt. Open the Gcell and extract the micro-cells (4 x 12v micro-cells) = 1 x 48v Gcell. Disassemble the micro-cells (tapping strips go for cycling), cells in good shape maybe reused, poor and bad cells go to final recovery. Gcells get rebuilt from new cells and new tapping wire. Reusable cells may go into games, laptops, flashlites etc where shorter lifespan is not so critical.

   Because we have almost all cars, truck, suv’s using 12v systems and the 4 x 12v micro-cells make our Mini-packs (Gcells) we need to bring the 12v junction out as a 3^rd terminal on each Gcell so it may be used in the first position of each bank.

Resale and recovery value

   People have two options maybe more when it comes to vehicle recovery value. The Motor, Inverter, Electronics, and Battery Pack are totally salvageable from a wreck or worn out car. It is unlikely that the insurance will offer you much. That 2000 malibu which the insurance writes off at $2200 as a gas vehicle will likely still be $2200 as an EV even though you have $17,000 invested and only used up 1 of 15 years life. The true value is $15,866 + $1000 for value of body. A better choice is to buy it back as salvage $50 remove the Motor, Inverter, electronics, and Battery Banks for reuse in your next vehicle or resell them and scrap the rest. On the other hand you want a new or different car. The auto lots are not your friend.
   They understand ICE, that looses $2000 the minute you leave the lot. An MRSP of 30,000 = 30,000 – mileage/10 – 2000 so if car is over 280,000 miles it has trade value of 0. Another vehicle with same MRSP with 80,000 miles might be worth $20,000 trade-in if not too old and in great condition. This is because ICE has lifespan of 300,000 miles but an EV has lifespan of 1,000,000 miles on EV part and 300,000 miles on the body. If you decide to sell privately you will need to show records proving how long the batteries were in use which includes odometer at battery change and current odometer.

   The whole industry is in for a shake-up if all vehicles have to be electric by 2040. 24 million vehicles in north America will have a value of 0 in 2040 unless they are electric. A look at the ford lightning F150 vs F150 gas reveals, $51,000 vs $38,000 ($9,000 is value of ICE parts) so $32,000 is their claim to EV over the $29,000 chassis. The specs aside from some bells and whistles claim 10,000 lb towing on the EV vs 14,000 towing on the ICE which is 1100 lbs more than my research showed. Range was stated at 230 miles to 300 miles vs 450 to 550 miles but they leave off the Kw of power so I have a hard time calculating true Battery Pack specs. $32,000 suggest a 4 bank equivalent = 160A and presuming they are using 384v standard that says 61.44Kw, they don’t give the GVWR or GCWR but if we use my figures 5580 lbs that says 61.44/0.558 = 110 miles not 230 to 300. To attain their figures we need 350A of battery. 8400 cells @5A 21700 cells at $3.81 each which is possible if buying in bulk like an auto maker does. For our concept we would have 35 cells in parallel x 15 cells in series per Gcell, and 8 Gcells in series per bank with two banks.

     To enclose such a Gcell you want it to be safe for operators, ventilated, short proof (conductivity safe), and reasonably light. Our Motorhome Gcells are 17.28 lbs each. The 48v cluster is 259 lbs and our bank is 2073 lbs with total pack weight of 4146 lbs. This creates a big problem. For 100 mile range we are 2303 lbs over weight when towing a car and still 1137 lbs over weight without the car. Cutting the range to 50 miles (83 kms) removes 1 bank worth of weight 2073 lbs. This means we are 230 lbs too heavy towing a car and 936 to spare without the car.
     The safest Packs are those with:

• Plastic or fiberglass structure so that people can be kept away from extreme energy supply..
• No Exposed High voltage or high current connections
• Metal re-enforced to withstand weight and also to protect from road hazards.
• Not too heavy to be managed.
• Easily mountable.

     For very practical reasons, each bank needs temperature monitoring and control, Voltage Balancing, Charge balancing, State of Charge, State of health, and functional control. BMS is the go to method of protecting the battery banks. It isn't as straight forward as they lead you to believe. Yes the BMS protects the Battery from over voltage, over current, over temp during charging and shuts the whole process down if it encounters any such condition. It can jump in if there is a short circuit so as not to damage the battery. Under live operation, BMS is both good and bad. It tries to balance all batteries to be at the same voltage either passively or actively. But voltage does not have much to do with it compared to SOC, SOH When one cell reaches full charge BMS stops charging all cells it is in control of. When one cell reaches maximum depletion, BMS cuts all it's cells out of circuit. Not what you want at all in an EV application. So we need to investigate what will work best and safest.
Making custom Gcells from cells

   The cells that are used to make up Battery packs come in 3 basic styles and a multitude of Amperages and qualities. China produces the least expensive but also the poorest quality cells around.
   Our target will be high quality 32700 liFepo4 cells rated for 6A per cell.

   Gcells are commonly made of blocks of 2x5, 3x5, 4x5, 5x5 or combinations of them. If you need 12v then you need 4 series Gcell-blocks. For 24v you would have 8 series Gcell-blocks and for 48v you would have 15 series Gcell-blocks. Note cells are 3.2v and a 12v battery is generally a 12.6v to 12.8v battery. By the time you make it to 48v, 16 blocks would make 52v not 48v. But 15 blocks works out to 48v precisely.

   Each time you combine another cell in parallel the current goes up by the cells current value. Always keep cells with-in each Gcell-block of the same type and rating. A 48v 200Ah Battery would take 15 series pack-blocks of 34cells at 6Ah in parallel. So each Gcell needs 510 cells. Each of the Gcell-blocks would be 8rows x 4cells and one row of 2cells. (~9" x 4" x 2.5"). The whole bank would have 5 Gcell-blocks x 3 Gcell-blocks (27" x 20" x 2.5"). The weight of the bank is about 163.84 lbs.

   This design seems more feasible with 4 micro-cell blocks in an 19” x 11” x 3” shape or done as 10” x 10” x 6”. Add a 16 pin connector with pins 1 to 15 going to each (-) and pin 16 going to +48v and we have BMS ability.

1 bank would be 10” x 10” x 48”

   So it's time to look at the equipment you will most probably need to make battery packs.

• Multi meter : Volts / Amps / Ohms measurements
• Soldering Iron 35watt or better.
• Spot Welder : to interconnect batteries.
• Glue gun : secure Batteries into enclosures
• Heat gun : wrap connections to make them safe.

• 3DPrinter : make custom enclosures.

And the supplies you will need to make battery Packs

• nickel strips : interconnect cells.
• plastic 1x2, 1x3, 1x4, 1x5 battery forms
• weld rods
• 1.75mm 3d filament (multiple colors avail.) 3d print enclosures.

• Gimp / FreeCad / 3D print software.

Until you have all the equipment in place there is little need to start on the project.
The Spot welder is the first and most important thing needed to make battery packs. Heat from soldering irons can damage the batteries fast so avoid doing that!

Make a simple battery pack

You have some up front decisions to make about the pack you are about to make.

• Will the pack block be Parallel cells only or Series/Parallel?
  Parallel only pack blocks all the batteries of all rows have the Negative all connected to each other and all the positives likewise. Current is sum of all cells additively.
  Series / Parallel pack Blocks each row connect cells in parallel but columns are connected in series.
• Will the pack have internal BMS?
  With BMS each series cell is monitored and balanced. End user does not get any visual report of cell conditions.
• Will the pack have internal Cell logging with alarm.
  Cell logging provides a voltage readout display that cycles through each of the connected series packs. The alarm goes off if a pack drops below minimum set voltage.
• Will the cells have temperature monitoring built-in
• Will the packs be centrally recharged or individually recharged.

• Will there be active coulomb counting for strict capacity measurement.

Capacity methods

Coulomb counters check Amps


Cell loggers check voltages

Fully charge all batteries and let them rest for a least 5 minutes then measure them so that you make sure each row has identical voltage. Ideally you also need to chart internal resistance and here is how.

Internal resistance

     Make a spreadsheet for your cells. For each cell measure the open voltage and record it. Pick a resistor and record it's read value. Put the resistor across the cell ends and measure the voltage across the known resistance. Record this next to the battery it refers to. V=IR so I=V/R. With the now known voltage across the resistor and known resistance we can calculate I. And knowing I, we can use (Vopen -Vload) / I = Rinternal. So for each cell record the Rinternal. Any cell with a high internal resistance will not work well in a Gcell. Are you sure you can trust a Gcell was tested properly and balanced properly before you got it?

     Before you begin making the packs it is important to closely measure the voltage of each cell and group them such that all cells per Gcell read the same. All cells in a parallel bank will gravitate towards the weakest cell's voltage. This makes it difficult for the BMS to level out the batteries consistently. You also need to verify the internal resistance of all cells to be in a parallel branch. This is done by measuring a resistor accurately and record it's resistance. Then place the resistor across the cell terminals and measure the voltage with the resistor added. Subtract the voltage with resistor from the open circuit voltage to get the voltage drop. Compute open voltage /Resistance (R) to get current (I). Calculate Internal resistance as Voltage drop x I . Any cells with far out of line internal resistance should be allocated to some other project not critical.

     Build your forms to accommodate the Gcell arrangement. In our case for a 10” x 10” x 6” Gcell we can go with 8 cells x 7 cells x 2 forms and 7 cells x 7 cells x 2 forms. For 32700 cells the forms are 1x2 or 1x3 but for 18650 the forms are 1x2 1x3 1x4 1x5 and even more types. If we connect 2) 1x3 and 1) 1x2 end to end and do 7 rows of that we have 1 form made. We repeat form 2, then connect 2) 1x2 and 1) 1x3 end to end and 7 rows of that we have form 3 made and repeat for form 4. Observe polarities ! All 7 columns in a row must be all (+) down or all (+) up. Row 1,3, 6, 8 should be (-) down, with Row 2, 4, 5, 7 being (+) down.

     Once all cells are in place secure the top frame. We now need to cut tapping strips in Preparation to wire the cells. Remember these cells are fully charged.

We will connect all (+) in each row together (Parallel) and connect short Tapping strips between (+) and next rows (-). Row 1 (-) also gets all 7 columns connected. Each (-) row gets a Tapping strip with a wire on for the BMS and row 1 (-) get heavy wire to (-) terminal, Row 5 (-) gets heavy wire to (+12v), Row 8 (+) goes heavy wire to Row 9 (-), and row 15 (+) goes heavy wire to +48v

     This example shows (+) row with all columns connected in parallel and in series with next row. In this example row 1 (-) is (- pole), row 1 (+) has (+3.2v) . Row 2 (+) connect all (+) together and all (+) wire to row 3(-). And row 3 (+) all connect together and a wire to (+9.6v) as this is a 9.6v Gcell with a 3,2v tap.

To split or not to split

     When it comes to high voltage battery there becomes a very difficult problem. We have 15 cells in series and 7 cells in parallel to make 48v. The BMS needs to monitor each series cell row to balance them. Then we take these 48v gcell blocks and connect them in series to create the 384v bank and then connect two identical banks to make the 384v pack. Our most economical charge source is 57v such that we can charge direct from solar and / or convert 120v AC to 57v DC and charge from a shore line. Converting 57v to 420v DC to charge a 384v DC pack is extremely expensive and quite loss prone. Manually disconnecting 48v blocks so they can be charged individually is time consuming and potentially hazardous. So I needed another approach. the 48v blocks are in series during vehicle run operation but, and there is always a but, what if we electronically convert the series blocks into parallel to charge them.
      Enter the MOSFET it can handle high currents and can be switched on or off with a low voltage signal.

    High power mosfets like the irf540 N-channel can handle the high voltage and current in the arrangement but, and there is always a but, it take 2 mosfets to replicate the triac due to properties of the diode body of the mosfet. The layout above is using the mosfets. Two mosfets are used between each battery block and between the first and last battery block and the +384v and traction ground. So we have 18 Mosfets. Then there comes connecting the (+) and (-) of each battery block to the charger. The mosfet uses 4 per battery block. This description is for only one bank. We need to do this on both banks.
     So we have 48 mosfets per bank. To save us from a PCB size nightmare and wiring nightmare, we can connect 6 Mosfets to each 48v block along with the BMS so that now we have 16 wires confined with-in each block for BMS and a simple (+) and (-) (En) (Chrge) (chrg+) (chrg-) passing from block to block. Special note: During RUN system ground = Run ground and charge ground is disconnected. During charge, system ground = first 48v block ground, Run ground is disconnected and charge ground connects to all block (-).

    Ignoring the right hand side of the schematic above, (BMS part), we have the new 48v switching circuit that will be at each 48v block. Prev-grp applies only to the first 48v group and it connects to RUN GND. Q4 and Q5 are used to connect or disconnect RUN GND to Block (-). On all other 48v blocks Prev-grp Q4 and Q5 aren't used. En chooses connect or disconnect blocks. Block (+) and (-) connect across the 48v block terminals. Chrg (+) (-) are the charging source and they connect across the block terminals when grp-sel is active. Block (-) connects to Next-grp of the previous block.
     So back at the computer, it is told to charge the cells by the operator (you). It sees it has 94,000 ticks (5958 ticks per amp) or 15A left. It knows the pack is 120A or 714,960 ticks when full. So it selects Charge Enable and unselects Drive Enable. At the battery pack, all Mosfets between groups of 48v stop conducting. All Group gcells connect to charger in parallel on both banks. Each time .00017A goes into the battery group, 1 tick occurs and so the computer adds 1 to the ticks. When the ticks add up to 714960, the computer unselects Charge Enable and selects Drive Enable. Back at the batteries, all gcells return to series and are disconnected from the charger. When all is done the computer looks to see if the operator selected shutdown when charged or not. If shutdown then turn off everything otherwise switch to main screen and wait.

     Since the topic of high currents of the battery packs has been mentioned often, we need to address it. Lets say our Battery source is 384v @ 288A like we have. From the research on handling high voltage and current they make a very valid point. It is highly dangerous to have a power source over 100A continuous and in many jurisdictions it is even criminal. Most people own a car of some sort. It has a battery that is usually 65Ah or higher and this battery also has another rating 800 to 1500 CCA which refers to cold cranking Amps. Since the CCA is used only during the starting, it is deemed non-continuous and safe. Our 288A pack follows the same guideline. During the first half cycle 1/120th of a second at motor start it draws 200A but then draws beteen 0 and 10A depending on load and speed. It's kinda like if we directed all water from Niagra falls into your shower at home. Use of the whole all at once would drown you but using a tricle is enough and great.
     The DIY sites abound and talk of 600A to 1000A systems. They are talking about the current used over the whole range to travel not the typical current draw at a moment in time. If it were over a moment in time the maximum range would be maybe 2 miles. It is over the whole range. so if you have 56 mile range, and it uses 560A to do that range, you are using 10A per mile. and if you are doing 60mph then you are using 10A per minute.
     Looking at AC induction motors, they are normally listed by wattage not by current.
     Below is a switching circuit on the left and a bms circuit on the right which we don’t need right now in the fiscussion. We would attach a switching circuit to each 48v Gcell and control all the charge and all the run leads together so a charge enable switches all Gcells to be in parallel and a run enable switches them back to series.

Conclusions:

The subject of this evaluation was a 1994 Gulfstream Class A Motorhome. The scope of this evaluation was to determine the feasibility of converting such an old vehicle into an EV-vehicle. The body was aged but sound. Tires, wheels, hubs, rotors, brakes, steering components and axles are in great shape. Door seals, Glass and seals, Wipers, and trim must be brought up to standard. This constitutes the bulk of the road worthiness of the vehicle.

Running lights for markers, signaling, brakes, reverse, and license plate will be changed from 12v incandescent to 48v LED and the headlights will remain as original.
The following are subject to removal:

• 8 cyl engine .... 485 lbs
• Starter .... 6 lbs
• Fuel injector / carborater .... 19 lbs
• Altenator ..... 9 lbs
• EGR, ICM, FICM
• Exhaust manifold .... 21 lbs
• Transmition 165 lbs
• Exhaust piping, Catalytic converter, Muffler ....80 lbs
• gas lines, Fuel tank and Fuel ... 525 lbs
• 5 x 12v Battery .... 425 lbs
• ................1735 lbs

as they have no purpose in an EV.
The interior will be changed as follows:

• Remove Radio .... 6 lbs
• Remove Heater control .... 8 lb
• Remove Instrument cluster ....3 lbs
• Remove doghouse and install trap door … 25 lbs
• Restructure the Dash for a smooth appearance.
• ......................42 lbs

The vehicle has a GVWR of 17500 lbs. After removing all the above we have recovered 1777 lbs. But we also now have no way to move.

A fresh start

      I determined that the best way to power a potential EV-Motorhome would be a 3 teir approach. In teir one we have a 384v battery pack made up of two 384v banks in parallel that can each be switched in and out of circuit electronically. In teir two we break each bank down in to 8 Gcells that are run in series except when they are being charged. Each Gcell is 48v. Each Gcell has 15 series cells with 7 or 14 or 24 parallel cells to make 48v @ 42Ah or 84Ah or 144Ah. Finally, each Gcell is made from type 32700 lithium ion phosphate cells. The third teir concerns power for all electronics except the traction drive. It is the very first 48v Gcell of the first bank of Gcells. This single 48v block is used to run lights, fans, computer, pumps, windows, accessories and has a tap. The tap is at 12v.

     In charge mode, the Gcell blocks that are in series when in run mode become linked in parallel in charge mode. This takes advantage of a low cost 57v method of charging. Each 48v block has it's own BMS and is charge monitored for accurate results. Each cell has 6A capacity.

Therefore
14 cells in parallel = 6A x 24 = 144A
15 cells in series = 3.2v x 15 = 48v per Gcell 115lbs ea.
8 Gcells in series = 48v x 8 = 384v per bank 920 lbs
2 banks in parallel = 384v @ (2 x 144A) = 384v @ 288A 1840lbs
384v x 288A = 110,592w = 110.592 Kw
17,500 lbs - 2277 lbs = new curb weight = 15223 lbs
added dash computer , canopy fusebox , charge controller, Motor & Inverter 175 lbs
added 2 banks of 8 x 48v battery mini-packs 1840 lbs
added solar charge array 551 lbs
New curb weight = 17,808 lbs = GVWR ( 308 over weight)

As an Alberta used motorhome it does merit conversion to EV and the battery planning, solar planning and Universal dash design does make conversion of any vehicle to EV viable. Range per charge without a toad 110.592/1.7808 = 62.1 miles (103 km)

At $28,800 plus labor costs it has merit as an EV.