I think one of my cells has failed. Can I try to recover it and/or questions on replacing it.

[dfinn]

2.5 years ago I built my first LiFePO4 battery. A 100AH battery using these cells:

Just purchased 4 BATTERY HOOKUP 3.2V 100ah MODULES

Just purchased my first LifePo4. For my first DYI project. I will update everyone on these batteries when I get them. Looks like they are hinting that they may be from the same supplier that Battle born uses...

diysolarforum.com

and a JBD BMS. The battery has been great up until very recently. A few days ago I was loading up for a winter camping trip and I checked on the battery and it was totally dead according to the BMS, it was reading 0% and 12.something volts. I brought it inside to warm up and connected it to my Victron 10 amp charger. It now will only charge to 75% but is still functional but with reduced capacity. It looks like I have one cell that is spiking it's voltage early and causing charging to stop early (there's a term for this but I can't remember what it is)

up until this recent issue, the BMS always said the battery capacity was 108AH but you can see that it has it down to 75AH now. You can also see that cell #1 has a much higher voltage than the others. This battery lives a tough life rattling around in the back of my truck camper and I don't usually take it out in the winter unless it's going to be really cold for long periods of time (well below 32 fahrenheit) but I was hoping it would last a bit longer than 2.5 years.

I'm thinking I probably need to start from scratch with new cells but wanted to post here first.

1) I've got a Victron charger that has "recondition" modes, is it worth trying this to see if the cell will recover?
2) Is replacing a single cell an option? If so, does anyone know if these cells are still available? It does not look like Battery Hookup carries them anymore.
3) If I need to buy new cells, what should I be looking at? I went with these cells because they used cylindrical cells which were supposed to be more rugged and didn't require any compression. What would be good cells to use for a battery that was going to see a lot of vibration in the back of a truck camper?

 

[LakeHouse]

1) I've got a Victron charger that has "recondition" modes, is it worth trying this to see if the cell will recover?

Absolutely not. That's for lead-acid and will just trigger Over-voltage protection from your BMS.

2) Is replacing a single cell an option? If so, does anyone know if these cells are still available? It does not look like Battery Hookup carries them anymore.

You could replace an individual cell, and it doesn't necessarily have to be identical, just look for something with a similar Ah rating to the ones you have already.
But you probably don't need to do this. You just have a cell that's out of balance. You should disassemble the pack and do a top balance, instructions here.
Alternatively, you could charge to a high enough voltage to let the BMS passively balance the cells, but that would likely take a very, very long time.

the BMS always said the battery capacity was 108AH but you can see that it has it down to 75AH now.

Your BMS doesn't know the capacity of the cells it's connected to, you have to tell it. Not sure how that setting would have changed, but it looks like it has. It might be worthwhile to post the rest of your BMS setting here so we can have a look and see if anything else looks strange.

 

[Partimewages]

It looks like you have one high cell. I would charge the pack at a very low C rate to 13.6. See what the current does. Then bump the voltage to 13.8.
3.4 per cell is about 100% but it may take a while to get all the cells there and completely filled.

 

[Checkthisout]

Disassemble and group balance cells and then reassemble and re-test.

 

[Brett V]

I'll bet your pack is just terribly out of balance. You need to disassemble the pack, parallel and top balance.

 

[dfinn]

How does a pack get "terribly out of balance"? This battery had been fine until I found it dead the other day, as far as I know there was no load on it although it is possible I had forgotten to turn something off in the camper but I don't think this is the case. Working on getting screenshots of the BMS settings now...

 

[Checkthisout]

How does a pack get "terribly out of balance"? This battery had been fine until I found it dead the other day, as far as I know there was no load on it although it is possible I had forgotten to turn something off in the camper but I don't think this is the case. Working on getting screenshots of the BMS settings now...

Running it dead balances the cells to low voltage, especially if the low voltage cutoff was set very low.

 

[LakeHouse]

How does a pack get "terribly out of balance"? This battery had been fine until I found it dead the other day, as far as I know there was no load on it although it is possible I had forgotten to turn something off in the camper but I don't think this is the case. Working on getting screenshots of the BMS settings now...

It just happens over time. Cells charge and discharge slightly differently, and if you don't give your BMS adequate time to do it's thing to balance, eventually the State of Charge of the cells drifts a little in relation to each other.

 

[LakeHouse]

Running it dead balances the cells to low voltage, especially if the low voltage cutoff was set very low.

No, it absolutely does not. The BMS will cut off discharge when one cell is below the low voltage disconnect level. At that time, the other cells may (probably do) still have some charge remaining.

 

[Partimewages]

The BMS does not track AH very accurately. None of the cell voltages appear to indicate a bad cell. Since the battery ran down as you say something ran it down and likely the BMS shut down on low voltage protection.

 

[dfinn]

I don't think I've ever changed or set any of these settings, this is how it came when purchased from Current Connected. If I recall, the BMS auto detected the initial capacity at 108AH when I did a full discharge and a full charge.

 

[Brett V]

How does a pack get "terribly out of balance"? This battery had been fine until I found it dead the other day, as far as I know there was no load on it although it is possible I had forgotten to turn something off in the camper but I don't think this is the case. Working on getting screenshots of the BMS settings now...

You were reading zero volts from the BMS before you started charging so it's likely the BMS shut down for a low voltage condition. All four of your voltages are in the flat portion of the charging curve and therefore mostly meaningless. You need to get the cells all to at least 3.6 volts.

 

[Partimewages]

Did you ever top balance the pack when you built it?

 

[dfinn]

You were reading zero volts from the BMS before you started charging so it's likely the BMS shut down for a low voltage condition. All four of your voltages are in the flat portion of the charging curve and therefore mostly meaningless. You need to get the cells all to at least 3.6 volts.

I never said it was at 0 volts?

 

[dfinn]

Did you ever top balance the pack when you built it?

I did, 2.5 years ago.

 

[Brett V]

Do a BMS read function to populate the screens

 

[Brett V]

Ok, zero %

 

[dfinn]

Do a BMS read function to populate the screens

thanks, sorry about that

if I recall, when I found the battery it had disabled the Discharge and was flashing under voltage.

 

[LakeHouse]

if I recall, when I found the battery it had disabled the Discharge and was flashing under voltage.

You don't show it in the screenshots, but there will be a 'cell undervoltage protection' setting, and you would have had one cell go below that, which caused the BMS to disable discharge.
For the settings shown, I don't see any problems, except that you should disable "Bal. only when charging". There's a description of why here. It might help to keep your pack from getting unbalanced in the future.

 

[dfinn]

You don't show it in the screenshots, but there will be a 'cell undervoltage protection' setting, and you would have had one cell go below that, which caused the BMS to disable discharge.
For the settings shown, I don't see any problems, except that you should disable "Bal. only when charging". There's a description of why here. It might help to keep your pack from getting unbalanced in the future.

Sorry, that got cut off. Cell undervoltage is set to 2500 mV for Trigger Value and 2750 mV for Release Value.

You say there aren't any problems, do you think I should just keep using the battery as normal and not worry about the reduced capacity that the BMS is reading? Do you still think I should disassemble and do a top charge?