The method of testing has been to use three 1.2Ohm 1kW resisters in series. These then draw about 21 amps from the battery pack and I time it until the low voltage trips on the BMS. With this draw I would expect to get about 2 hours of discharge (50Ah pack 80% usable). After that I would charge until HVC. After the first two cycles the pack was fairly well top balanced with all cell groups going into shunt mode before the HVC was tripped. Now my charger is rigged to go to 87.6V (24 * 3.65v) but the BMS is designed to trip at 86.4V (24 * 3.6v) so I will have to look at trimming it down a little.
- The BMS works. It cuts out the charger on high volts and also cuts the throttle at low volts
- The wiring from the cells to the BMS should be fine as is
- I have some bad cells
Number three is a concern it appears that at least some cells in the 7th parallel set are not holding capacity. That set consistently hit low voltage first and at about 1.9kWh which is about half the expected capacity. Also the high voltage is tripped when the whole pack is at 83.7volts when it should be 86.4V. Now do you think that the 7th set would be in the inner or outer sections of the pack? You guessed it, they are in the inner… so I will be disassembling the pack (unfortunately) to locate and replace the bad cells. I might even test the pack outside the bike before fitting it again
I hope to do that this week.