Finding the bad lifepo4 cell

[Donald Siegel]

I have 8 of the generic used Chinese lifepo4 100-amp cells assembled into a 24v battery with a Daly 40 amp BMS. When charging the battery with my MPP Solar with correct lifepo4 settings I smelled a chemical fume right at the start of the charge, so I quickly switched them off. I checked the bus bars (thick copper bars) and the BMS connections everything was tight and intact. I removed the BMS assuming it was the issue and tried a charge again with the same result, so I disconnected the battery and moved it to a fire safe spot on the cement. I will disassemble it and check each cell to see which one(s) are shorted or damaged. I assume I should just charge each one to 3.4v with a 2-3amp starting current and a 3.6v charge voltage until my amps are zero and see which fully charge to 3.4v and can hold that charge a few days? Is there a better way to find the bad cell(s)?

 

[electric]

6 cells don't make a 24V battery, maybe a typo in your post? What were cell voltages right before you started the "smelly" charge? What about right after you turned it off? Are cells physically swollen or have their vents ruptured?

 

[Sojourner1]

I literally was just typing that when it showed a message was just posted.

 

[Donald Siegel]

Yep wrote it too quick from work, 8 cells, but the main point was how to find out how to assess the problem. No obvious swelling. I kept a cell meter 8 connection intact and could cycle through the voltages of the cells and they stayed voltage matched on occasional testing. I just put it aside for now as I have big gel batteries as well and this was a backup bank, I’ll check the voltages as they have sat for a few weeks and I’ll disassemble the battery and inspect each for swelling and update this thread. I fixed the typo on the first thread.

 

[electric]

Yep wrote it too quick from work, 8 cells, but the main point was how to find out how to assess the problem. No obvious swelling. I kept a cell meter 8 connection intact and could cycle through the voltages of the cells and they stayed voltage matched on occasional testing. I just put it aside for now as I have big gel batteries as well and this was a backup bank, I’ll check the voltages as they have sat for a few weeks and I’ll disassemble the battery and inspect each for swelling and update this thread. I fixed the typo on the first thread.

Sitting for a few weeks is actually a good thing as you can check the voltages and see how well they hold up. Badly damaged cells would not hold the voltage for this long. If voltages are around 3.3V without a large spread and cells are physically not swollen or ruptured, then it might just be all OK.
Sometimes you get a little whiff of LFP electrolyte even from normal charging, depends on how sensitive your nose is and how small the area was around the battery. With little airflow around it might have seemed like it was worse than it really was.
There should not be a strong smell and no steam, but a little whiff might be OK. Try to pinpoint the exact source of the smell, maybe its not even from the cells. Also check the charge current to make sure it's within expected range, so nothing is shorting out.
Most importantly, use a BMS and don't let any cell go above 3.65V at the end of charge.

 

[SolarRat]

New electronics often emit weird smells. It's usually just some leftover assembly chemicals on the circuit boards burning off and nothing to worry about. So hopefully that smell was coming from the charger and not the battery?