BMS Mistakes

Check it once, check it twice, take a shower, go fix the problem you realized you made, then plug everything in and try it…. or at least that’s what I should have done…

After many hours of measuring voltages, making connector pinout diagrams, soldering 216 wires, and again validating the cables with a multimeter… it appears one more check was needed.

The upper and lower 32 cells were wired correctly, but the middle pack had a different wiring pinout. I caught this, but was defeated by the simple observation (or lack there of) that the way the middle pack was attached by bus bars made negative and positive sides opposite that of the other two packs.

I plugged in the BMS and was happy to see the first 32 cells perfectly populated with correct voltages, but then noticed the BMS wasn’t seeing the middle 32, but again perfect for the final 32 cells. I stared at it for a while, but just couldn’t figure it out and just decided to go to bed.

The next morning within the first 2 seconds of stepping into the shower I realized that I had wired every cell backwards because I didn’t notice the pack pos-neg had switched sides because of the bus bar layout. The multi-meter check had passed my mind because I just simply overlooked the negative sign on the meter and paid attention to the differences in cell voltages looking for pins I may have switched.

After work that night I went home and rewired the harness hoping to plug it in and move on from that mistake and continue to make progress over the weekend, but it appears that the BMS suffered internal damage from the cells being reversed. Oddly it seems to have affected the entire BMS as all the cell voltages seem to be at odd sporadic values. Unfortunately the BMS support is only Monday-Friday so it looks like the BMS side will be on hold for the rest of the weekend.