Elithion, dougingraham, thanks for your expertise!
I wanted to try one charge before coming back to answer, and as usual putting all in place took much longer than anticipated.
I forgot to mention in my original post that we wanted strong Regenerative Braking
and a cheap BMS system. That was one on the reasons for this experiment, as cheap BMS are no able to handle the higher charging currents (>50A).
Now, about our first charges. When we put the system to charge, we tested the voltage of several cells and compared to voltage on BMS plugs, to detect any voltage fall.
We have 24 cells. Cell 1 plugs on the negative wire, cell 24 in the positive.
What we found was important voltage falls in the extremes on the pack, but none in the intermediate cells.
Cell 1 -> 3.44 on bms, 3.30 on cell
Cell 2 -> 3.33 on bms, 3.31 on cell
Cell 15 -> 3.31 on bms, 3.31 on cell
Cell 24-> 3.40 on bms, 3.31 on cell
Does anybody knows what could be going on here? Are our wires too thin/large?
you are right, but we have not found a BMS like that as cheap as we needed. We are using one of cheapest ones in the market, I think. Only e-bike and RC ones are cheaper!
as you predicted, we have had no problems on pluging/unpluging the BMS.
We are thinking now about splitting charger & BMS, so at least we can load the charger on the Quad and be able to perform Opportunity Charging
Thanks for the fuses suggestion, we will implement it.
About undervoltage control, the controller should protect us (it has a setting for that) and we also have a cheap cell state display system. When a cell goes under ~3V it starts beeping.
The whole thing about bottom balancing is new to me. I have read some references before but I still have to really learn about it.