Intermittent Cell OverVoltage on OVerkill 16S BMS

[Morgan360]

I'm hoping that I did something wrong, and the BMS is still good, but I can't figure out why my BMS shows 3.8 volts on cell 16 and 2.8 on cell 15, but only intermittently.

The pack is a 16S configuration of 277 GFB cells in a mobile application and about 18 months old. Not shown in the pics is the battery pack cover and slow-blow fuse. It is connected to a Growatt all in one and nothing else. The pack is in a steel compression fixture with neoprene-like insulation between each cell.

I recently top balanced the pack in parallel with a power supply due to cells 1 and 15 getting a bit off voltage. After reconnecting everything, it worked fine for a day or so, then it disconnects due to either cell 15 or 16 overvoltage and the other of the two is undervoltage. This happens with it just sitting there, not moving, not charging or discharging. It will reset and work fine again for a day if I disconnect and reconnect the balance leads from the BMS, then happens again All connections on the pack have been lightly sanded, cleaned and torqued. I'm at a loss here and am hoping someone here can help.

Not sure if its related, but my settings in the BMS did unexplainably change themselves recently. After looking closely, the overcurrent shutoff amperage and pack total capacity had changed to weird values. I couldn't find anything else that changed itself.

 

[MisterSandals]

but I can't figure out why my BMS shows 3.8 volts on cell 16 and 2.8 on cell 15, but only intermittently.

I am 99% sure that your balance wires and/or their connections are to blame.

Have you tested voltages at the connector that plugs into the BMS?

pin 1 is negative
pin 1 to pin 2 should be ~3.2V
pin 1 to pin 3 ~6.4V
pin 1 to pin 4 ~9.6V
...

 

[mikefitz]

Check the connections of the buss bar and BMS leads at cell 15 and16. Measure the voltage directly on the cell terminals and compare to the BMS readings.

 

[Morgan360]

I'm still struggling with this issue. I verified at the balance lead pin outs that the cells are in order. I also recleaned all the terminals and retorqued, but it's still happening with no warning.

However, I did find a new error popping up in the logs. See attached screenshot

 

[justgary]

Perhaps you can gently pull on the sense wires at the cell terminal connections. I had a bad crimp on a sense wire terminal and the BMS was not happy. It was easy to find with a gentle tug on each wire.

 

[Morgan360]

I thought the same thing and tried that on my initial round of troubleshooting and I just did it again for good measure. Nothing appears to be loose.

Fyi, I also did that to the balance lead connections on the BMS and nothing loose there either.

 

[Alkaline]

Ok something is going on with these 16s JBD bmses. This is like the third or 4th post I have seen... Where is that coach guy he had to replace his BMS to get it it work it was reading voltages entirely incorrectly.