Battery Pack and Related Electrics Version 2.0

I spent the afternoon of my birthday playing around with a new Lithium ion battery pack design for the 914, if I ever return to civilization.

To save money and complexity, I'll keep the existing Curtis 1231C-8601 controller which is rated for a maximum 144V pack and 500 amps.  This is still sufficient for me driving through town.

Based on years of experience at EVTV with the China Aviation Lithium Battery Company (CALB) 180AH CA-series cells, I know how to bottom-balance them, charge them and discharge them safely.  This is in deference to the many YouTube guys building up Tesla-like 18650 packs from dodgy laptop battery packs.  I did the math to determine I need 42 of the CALB cells at a nominal 3.4V each.

I brought up an old SketchUp model I made a couple of years ago and worked out how to place these batteries and other components.  I'll fill up the rear battery box where the gas engine used to be and put the rest in the battery box where the gas tank used to be, with a good amount of space left over.

This means I can remove the 2 single-battery-sized boxes from the trunk and weld some steel plates into place, prime and paint and turn it back into a fully usable trunk.

I also gain all of the capacity of the battery box where the spare tire used to be right in the front.  I created shapes matching the sizes of the rest of the components I need and fitted them all into place.  This means the new TCCH 4KW or 5KW charger I'm looking at and its controller, the new GEVCU controller, the existing relay board and the existing DC-DC converter all fit inside the front box.  The TCCH is air cooled but the box already has an exhaust fan that switches on during charging, so it looks like it will be a perfect setup.

Cleverly I'm moving the 12V auxiliary battery from it's ugly, nasty, breaking-off-prone mounting bracket on the front of the front battery box to inside the gas tank battery box due to some newly available space.  I'll run the 12V wires down the passenger side of the frunk to the DC-DC controller and leave the high voltage battery pack wiring where it runs now down the driver's side.  There's even still a bit of empty space so I'll play with the position of the batteries to maintain side-to-side weight balance and fill the gaps with some stiff foam.

So, here's the layout.  I've also built up a list of to-do items, some must be done concurrently with this major upgrade, while the rest can be done at my leisure.  I'll bling up the installation by replacing the white plastic battery pack lids with transparent lids.

Energizing the 12V circuits

After the ignition switch was wired in, there was nothing stopping me from hooking up the battery and turning the key.  This should help me test the 12V circuits.

I had my son standing next to the battery with a fire extinguisher as I turned the key.  BEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEP!  I nearly jumped out of my pants.  I had tucked the horn wire into a space in the steering column, completing the circuit.  As soon as I turned the key, the horns went off at full volume.  I switched off the key and pulled the horn wire out.  I turned the key again and heard a click in the relay box.  I followed the diagnostic tests in the EA manual and immediately found a problem.  The green oil pressure indicator light is supposed to light up when the key is turned, indicating that the 12V circuit is on.  But the light didn't go on.  After tracing the wiring and checking with a meter, I found that the light bulb was bad!  I bought a box of replacement lights for the instruments, but that particular one still had its old bulb.  Lesson learned...  The rest of the EA tests with the batter and DC/DC converter were successful.

Next I tried pushing the electron pedal and heard the contactor engage with a loud clunk.  Success!

I don't have any of the original 12V devices in place like lights, blinkers, etc. so there was nothing else to test.  As I rebuild those parts of the car, I'll test them.

Front Battery Box Assembly

The last thing I tackled this week is the construction of all of the components of the front battery box.  The box holds batteries, but is also the platform for the auxiliary battery, the DC/DC converter and the relay board.  As with the contactor parts, I put the relays and the connector strips into another weatherproof enclosure.

Here's where things went horribly wrong.  The aux battery and DC/DC board mounts to the battery box via threaded studs and 1/2" long 1/4" bolts.  Unfortunately the holes were all the wrong size and the studs were not installed at the factory, as the instructions assume.  It took me a while to figure out the right stud to use, drill out the holes, install the studs, then moved forward.

Since I'm bolting a weatherproof enclosure into this area, I had to drill holes slightly below stock.  I also had to clean up the plastic welding bead on the inside joint.  I melted it with my soldering gun, then scraped away the excess while it was still warm.

Another big problem with the directions is it assumes a certain DC/DC model with bolt terminals on the top, not with a cable coming out the top like mine.  Reading ahead I see I'll have to double-lug some of the spade lugs to work around this problem, but I'm getting very flexible and creative now.

And finally here is the relay board in its enclosure, ready to have wires run into it.  I'll dummy everything up and figure out how best to run the wires into the box using probably three gland nuts.

This is the aux battery mounting area.  I'll have to pick up a battery tomorrow to be able to continue cutting and mounting the rest of the cables.  For the record, it's a U-1 style 12V battery, maximum size 7 3/4" L x 5 3/16" W x 7 5/16" H, with 1/4" bolt-on terminals.

Well that was the end of a long, hot week.  I think I need a break from the project for a while!