Getting to a full charge

[chrisblessing]

Greetings. I assembled a 120Ah LiFePo4 battery about 2 years ago, and installed it in my small camper. It has been a great performer, with few issues. That said, during a recent 6 week road trip which saw many days of little to no sun, the BMS shut the battery down until I was able to supply charging power with a small 4 amp charger, or when sunny, whichever came first. In the last 8-10 days I started seeing one cell with seriously low voltage, far below where the BMS ought to have shut everything down. I had a small active balancer in my kit and used it to see me through the rest of the trip.

When I arrived home I left the battery in place and switched the BMS to a a Daly 100a smart (bluetooth) BMS, and am no longer seeing any discrepancies between cells, but I'm also unable to get the voltage of the entire pack much higher than 13v.

I have now removed the battery, and using both my small charger as well as a bench charger, I am unable to get any of the cells to charge past 3.2v. I have tried both each individual cell, and the entire pack in parallel. I haven't yet done a capacity test and am guessing that is what comes next, but I wonder if anyone might suggest what else to look at.

Thank you kindly for your responses.

Chris

 

[sprint2freedom]

Sounds like it could be poor cell connections.. remove lugs and bus bars, polish them up and try again?

 

[Bud Martin]

"I have now removed the battery, and using both my small charger as well as a bench charger, I am unable to get any of the cells to charge past 3.2v. I have tried both each individual cell, and the entire pack in parallel. "

When try charging individual cell, what charging current are you able to see going into the battery, and how long did you let it charge?

 

[chrisblessing]

Sounds like it could be poor cell connections.. remove lugs and bus bars, polish them up and try again?

All connections are/were very secure. Thank you.

 

[chrisblessing]

"I have now removed the battery, and using both my small charger as well as a bench charger, I am unable to get any of the cells to charge past 3.2v. I have tried both each individual cell, and the entire pack in parallel. "

When try charging individual cell, what charging current are you able to see going into the battery, and how long did you let it charge?

I didn't try to charge individually for very long. My bench charger has a maximum current of 10a. Thanks.

 

[chrisblessing]

UPDATE: I reassembled the cells in series and ran my bench charger at its full 10 amps for nearly 8 hours when I finally saw some upward movement. I started monitoring every few moments suspecting that I had hit the last knee. Sure enough within 30 minutes the pack was nearly 14 volts.

I let everything chill, disconnected from one another, overnight. By morning all cells were sitting at ~3.59, so I reconnected the four cells in parallel and have been charging at 13.6 volts. Currently the cc is very, very close to zero.

I've got my fingers crossed that the batteries are fully charged and top-balanced.

Thanks so much Bud Martin and sprint2freedom. I'll update later after fully reassembling and reinstalling everything.

 

[chrisblessing]

UPDATE 2: the battery is performing well. Today, in full sun and with 2 160w panels in parallel the charge controller stopped charging right at 14.6 (the overcharge limit). BMS readings showed the same. So it appears that the original BMS was the source of my problems. Thanks again.