Okay, so, search for "bad cell," or "bad connection" on here, on you get a flood of results ? It seems like most people wind up needing to get in there and start trying to fix stuff before they figure out what's wrong; but before I go ripping apart my pack and testing things, I wondered if someone might be able to advise on where to start, just based on the BMS readings.
I'm running a 16s, 310Ah 3.2V LiFePo4 pack. With this, they're attached to a Daly 48V 16S 150A BMS (model R32U1, I guess), as well as a 5A active balancer.
I had a long adventure of top balancing the pack - spent days on a benchtop power supply in parallel, but could never quite get it up into the steep part of the charge curve. Finally opted to top balance it in series with the inverter, relying on the active balancer, where it got it within a few millivolts at ~3.45V before I stopped.
Anyway, after all that, I thought I was in business - but now I'm getting some problematic readings/behavior on the BMS while charging. It seems like all the cells have been discharged into somewhere along the middle of the charge curve (just from running some loads in the house), and they're all sitting at ~3.3V within a few millivolts of each other.
When the inverter goes to charge the pack, the first cell in the string quickly starts to spike up over 3.65V, cutting off the BMS (and, of course, the inverter freaks out... ?) - but then, the cell drops back down to within a few millivolts of the other cells within seconds of the charging cutting off. Seems too fast for the active balancer to be keeping up, and seems to be too big of a voltage difference (3.3V up to 3.65V, and back to 3.3V) for it to just be a runaway off-balance cell... I attached some pictures for reference.
The positive terminal on this cell did get messed up at some point while I was working on it--I needed to re-tap threads--but I thought I fixed it. Like, it feels like it's solidly connected... And I've also seen something similar happen when I had a different cell as the first one in the string (although, not so dramatically...). I have replaced the ring-terminals on the wires for the first few cells a couple of times too, just to make sure, but it seems to be acting more or less the same...
At any rate, any insight into what's happening would be super appreciated!
I'm running a 16s, 310Ah 3.2V LiFePo4 pack. With this, they're attached to a Daly 48V 16S 150A BMS (model R32U1, I guess), as well as a 5A active balancer.
I had a long adventure of top balancing the pack - spent days on a benchtop power supply in parallel, but could never quite get it up into the steep part of the charge curve. Finally opted to top balance it in series with the inverter, relying on the active balancer, where it got it within a few millivolts at ~3.45V before I stopped.
Anyway, after all that, I thought I was in business - but now I'm getting some problematic readings/behavior on the BMS while charging. It seems like all the cells have been discharged into somewhere along the middle of the charge curve (just from running some loads in the house), and they're all sitting at ~3.3V within a few millivolts of each other.
When the inverter goes to charge the pack, the first cell in the string quickly starts to spike up over 3.65V, cutting off the BMS (and, of course, the inverter freaks out... ?) - but then, the cell drops back down to within a few millivolts of the other cells within seconds of the charging cutting off. Seems too fast for the active balancer to be keeping up, and seems to be too big of a voltage difference (3.3V up to 3.65V, and back to 3.3V) for it to just be a runaway off-balance cell... I attached some pictures for reference.
The positive terminal on this cell did get messed up at some point while I was working on it--I needed to re-tap threads--but I thought I fixed it. Like, it feels like it's solidly connected... And I've also seen something similar happen when I had a different cell as the first one in the string (although, not so dramatically...). I have replaced the ring-terminals on the wires for the first few cells a couple of times too, just to make sure, but it seems to be acting more or less the same...
At any rate, any insight into what's happening would be super appreciated!