48V LiFePO4 bank with low cell; what could be the problem?

[apctjb]

A 48V-560AH LiFePO4 battery bank I built about 2 years ago suddenly has a low cell. Nothing physical apparent, connections all tight including the BMS voltage sense wires. System has worked flawlessly up until recently when it went offline because the BMS disconnected because of a low cell.

Curious to hear from others what the problem could be? Note that the bank is comprised of 2-280AH cells in parallel , 16 series. I am thinking of temporarily bypassing the BMS so I can charge up the bank and see what happens. Bad idea??

Photos below...

 

[sunshine_eggo]

A 48V-560AH LiFePO4 battery bank I built about 2 years ago suddenly has a low cell. Nothing physical apparent, connections all tight including the BMS voltage sense wires. System has worked flawlessly up until recently when it went offline because the BMS disconnected because of a low cell.

3.2X is a fairly low state of charge. It could just be that the cell has notably lower capacity than the others

It could be that one or both of the cells in that group have failed.

It could be that the battery is severely imbalanced.

I am thinking of temporarily bypassing the BMS so I can charge up the bank and see what happens. Bad idea??

I don't understand why bypassing the BMS would be necessary, and I wouldn't do that unless I had no other option. If it won't let you charge, simply reconfigure the BMS with parameters that allow you to charge.

 

[apctjb]

3.2X is a fairly low state of charge. It could just be that the cell has notably lower capacity than the others

It could be that one or both of the cells in that group have failed.

It could be that the battery is severely imbalanced

Thanks for the response! Of your list of options hoping it is option 1 or 3!

Reason for bypass is I am troubleshooting remotely and with my limited Spanish easier to describe how to swap some wires than describe how to navigate a somewhat clumsy user interface of the BMS. Hoping that with some charging can get cells back in range and then remove the bypass and limp along until I get a chance to get there...

 

[time2roll]

Is that cell pair also low at full battery charge? If so I would be looking at boost charging that pair to be full same as the others. This can be done with no disassembly. Verify voltage direct on the cell terminal with meter.

Otherwise I would be ordering a pair of replacements.

 

[KauaiMolokai]

Not an enviable dilemma. Anything you instruct those on site to do runs the risk of making things worse. Unless its life or death, the most conservative approach is to leave the system off until you get there, ideally with replacement/spare cells in hand. Good luck.

 

[apctjb]

Anything you instruct those on site to do runs the risk of making things worse. Unless its life or death, the most conservative approach is to leave the system off until you get there, ideally with replacement/spare cells in hand

That is the fall back option, but it will be 3 months and would like to get internet back online for security cameras, etc...

 

[KauaiMolokai]

I can maybe give a few suggestions I would likely do in your shoes. The over-riding goal being to not make things worse.

How long does it normally take, on average, to charge your battery bank up to full?

Do you have people onsite who can spend some time on working with your system for you?

If so, how technically proficient and reliable are they?

 

[apctjb]

How long does it normally take, on average, to charge your battery bank up to full?

Do you have people onsite who can spend some time on working with your system for you?

If so, how technically proficient and reliable are they?

First of all thanks for posting. Typically can charge the battery bank is less than a day if I have AC's off. Very limited availability of local technical help, a capable and willing gardener, with no technical background.

 

[KauaiMolokai]

No problem. I'm posting with the idea that an outsider's perspective might be helpful. I know very well the challenge of handling things remotely. Please read any suggestions accordingly. I'm no expert ;-)

Does the gardener derive any direct benefit from the PV system? Does the AC stay off when you are not there? Working on the system will require extra effort by the gardener. It could be helpful if he knows he will be compensated extra for doing this, and doing it diligently.