The batteries are all finally mounted in the car. To get here I spent months designing, fabricating, fitting, modifying, refitting, and finally bolting in the battery racks. It was a lot more difficult than I imagined it would be, but I guess that's par for the course for such a custom car. Now that the batteries are strapped in place it's time to wire them all up. Each of the rear battery clusters has 23 batteries, 46 bolts, 92 washers, 1 fuse, 2-4 copper bars, 22 bus bars, 3 twisted pair wires, and 24 BMS wires. The next step in wiring these all up is to build the BMS wires.
The BMS wires serve two purposes. When the BMS functions, a very small amount of current is flowing through the wires while the circuit board monitors the voltage across each cell. The current flowing out of one cell is not exactly the same as all the other cells in the cluster, and I'm estimating after 3 months, some will be around 1.5% more discharged than others (about 1 Ah). Eventually, this will cause the charger to stop charging prematurely and the cells will need to be re-balanced. The BMS boards each have three balance charging ports, and a balance charger will send current through those little BMS wires to do just that.
Each wire comprises a ring terminal where it is bolted to the battery, a 4 amp fuse, and the wire. To put these wires together I had to crimp the terminal to the fuse and solder it in place. Without the solder joint, there's a chance that the crimp could come loose and cause some faults. How do I know this you ask? Well, I'll just say that Joe highly advised the solder joint. So clip the fuse to size, crimp on the ring terminal, solder the fuse lead, solder the wire to the fuse, cut the wire to length, heat shrink over the fuse connections. That should be too bad right? Only a couple minutes and you're done. If you add it all up, that took about six and a half minutes. Multiply by 73 and that's how long it took to make all these dang wires!
Ok, the next step is to hook it all up. One of the terminals on each battery is aluminum. When you put aluminum and copper together you have the potential for galvanic corrosion. To get around this, you put a little conductive anti-corrosion paste and rub it in with a wire brush. After I got everything installed, this is what it looks like:
To keep things straight I got some sticker number flags and put one on both ends of each wire. Amazingly some places want to charge you $20 for a sheet of these stickers, but luckily I found some on Amazon for just a couple bucks.
Yeah yeah yeah, I know I'm missing one wire and I forgot to put the fuse in (if you look two pics up). And no, I swear I didn't do the exact same thing to the battery pack on the other side...I was up until 12:30 last night getting this done, so cut me some slack! So far, so good. Now I bundled all the wires together, zip tied them about 700 times, and collected all the ends. They're not all the same length anymore, so I have to retag them and cut them all down to the right length. I've gotta be really careful though because each of these are live wires! If I'm unlucky enough to touch two wire tips together I'll have to spend another 13 minutes making new wires plus another 30 minutes swapping them out. That also means don't clip more than one wire at once! So I clip, strip, then crimp a connector pin onto the end of each and now I've got three plugs to go into the plugs of the BMS circuit boards. I've got all the wires mounted on the batteries, but only 1/3rd of those connectors have been pinned out so far. Oh yeah, and I'm missing one wire.
I also got all the large 2/0 cables measured, cut, and crimped with lugs, so theoretically I'm all set to test out the controller on 230v. I just have to screw it all together. I'm a little battery weary and we've got friends visiting this weekend, so I'm not gonna push it an do something stupid in the testing phase. So after a weekend of R&R I'll be back next week to see if I can keep the magic smoke in the controller!