I built a 12s8p battery pack at the weekend using molicell 21700 cells from Fogstar. I am using the apex smart bms, seems to charge well but it seems to struggle to balance. What are some common reasons for this? The pack is spot welded using 0.2 x25mm nickel strip.
0.068 is a pretty high voltage delta, your BMS is gonna struggle to balance 8P anyway but if you can do a balance charge (Keep the pack on the charger for a few hours, monitoring it) that might help. If you notice group 10 keeps drifting high there could be an issue with its capacity but run balance and go through a few cycles first.
Also what are those round white circles with the B icons? Could that mean its only balancing those 3 groups?
So you guys reckon just cycling the pack a few times? Yesterday before the ride it was balanced fine. But after I had taken it off charge group 9 was quite high but the BMS leveled it all out over night before my ride.
Just went through similar issue with fresh 12s4p pack with recycled 40T cells. Go to settings and disable ‘‘Charge balance’’, connect it and disconnect it from charger to apply the setting. That way it will balance pack even when charger is not connected. Secondly, charge it to full and let it sit for few days. In your instance with pack this big it will take about 4 days to balance to 0.015v delta. A good way to avoid such dis balance to a big pack is charging battery to full every time you charge it, that way battery will have better chance to balance out. Also since it’s new pack, do couple of full charger and discharges (drive it till it hits 3.1v per cell, then charge it to full again and repeat)
Couple of other things:
-After long ride, don’t instantly connect charger to pack, instead let it sit for few hours for battery to ‘‘calm down’’ (it’s chemistry after all) and then charge it.
-0.06V delta is not great but not terrible, I would start worrying above 0.1/0.2v delta. 0.4v delta is super bad.
If possible, do a benchtest of your pack from full to empty SoC with intended contineous current.
This will give you a very good indication of your pack health, available capacity, voltage sag and even how much drop you have over the cables.
Building a pack and not testing it before going out is ludicrous
In my instance LLT failed to even do it at top of the range with ‘‘charge balance’’ enabled. Once I disabled it did the good old ‘‘balance by dissipating energy through resistors’’ quite nicely. Took two days however. LLT is funky and sometimes doesn’t act like regular bms’s
There is no oversight this way, I know.
But in my time, this app was very very unreliable. I can also show you a fried one. Bad experiences… if I had an iphone i might have kept it, that app was a lot less “china”