Lifepo4 mishap. Can they be salvaged?

[Pnw_steve]

Hey Everyone,

I have been presented with a learning experience....... I had a charger fail and I found eight (280 AH) cells puffed up a fair bit. The vents are intact. I know that cells are generally destroyed if they vent.

This is a new one to me. What do you all think? Has anyone successfully recovered batteries at this point?

I will try and get a picture up here in a bit.

Thanks.

 

[John Frum]

What is the current voltage of the cells?
If it was me I would discharge them down to ~3.29volts ASAP.
See if the cells start to deflate a bit.

 

[Luthj]

Photos please.

Cell bloating in this case is caused when the voltage gets high enough to break down the electrolyte into gaseous components. This gas formation is often between the layers of the cell sandwhich. The result is typically uneven internal resistance and capacity loss.

If the cells are used in a non critical application, some people continue to use the cells.


For all those reading, do not charge cells without a BMS unless you really know what you are doing. The only exception is initial top balancing, which should only be done with a properly adjusted single voltage power supply.

 

[Pnw_steve]

Thanks Luthj.


I was top balancing so no BMS.

If I had been charging a series string I would absolutely have had a BMS running.

I had a senior moment and left it running overnight unattended. It is my practice to turn things like this off or turned down to a trickle when I leave the shop.

Another lesson learned. Stick with a good bench supply for top balancing. I had a handful of Ebay/China buck/boost converters that I have used for battery charging. If you run them at more than 50% current for very long they die. Output goes to zero...... Until this one. When I checked the BB output with the battery disconnected was over 30 volts.

Inattention and cheap tools. Not a good combination today.......

 

[AussieSim]

30v = 3.75v

Not good, but probably not terminal, post some pics of the bloated cells.

Perhaps discharge then to 10% SOC and add compression, because the bloat on the middle they tend to splay apart at the bottom

 

[Luthj]

was over 30 volts.

I am guessing it was over 4Vpc

 

[Dzl]

I'm sorry to hear about this Steve , I hope the cells are salvageable. What was the highest cell voltage you measured?

30v = 3.75v

I think this is a misunderstanding, the pack was not being charged in series so I don't think that math would apply

I think 30V is what the failed buck/boost converter was showing after failure, unrelated/separate form the cell voltage

 

[Steve_S]

They may still yet be recoverable but with a little loss. Had the vents popped, they would be going to recycle, plain & simple.
1st thing first and all of this is a PITA but if done right, it saves your keister.
1- Discharge the cells to at least 3.60V each.
2- Compress the cells in a "Clamp" BUT NOT HARD...a Light Hand Squeeze tight and continue to discharge the cells till they reach 3.2 volts each.
3- While discharging below 3.60V, recheck the "squeeze" frequently, you want to keep it SNuG but not under serious pressure. As the cells discharge the bloat will reduce slowly, DO NOT FORCE or apply too much pressure, it has to be gentle.
4- Once all cells are at 3.200V evenly, then you can "squeeze" the cells to Hand Tight and let them sit for a couple of days with nothing connected, not even busbars across the cells. Over time you will see voltage changes but also the bloating will "SLOWLY" reduce. Remember to keep checking that the pressure is constant and even.

- Use "blocks" on the ends to distribute the pressure evenly and to prevent any one spot from getting more pressure.
- When completing (after 4 days of rest under pressure) you can then check to make sure they flattened out (may not be perfect) check your voltages per cell.
- Bring each cell (alone) up to 3.450 and allow the charger to "saturate" the cells to the point where they do not take more than 2A. All the while under pressure (compression).
- Once all cells have reached 3.45 & saturated, then you can reconnect them in parallel and take them up to 3.500-3.600 (no higher) and again allow to saturate down to <2A taken.
- Now the crappy part... At this point the cells will still settle a bit so give them a minimum of 4 hours, (12 is the golden spot).
-- Recheck the settled voltage, IF they are all close +/-50mv DO A HAPPY DANCE ! If within 100mv still okay and happy... too much more, then cell is suspect but NOT out of the game, a quick topping again should level it up so do that and retest after 4-12 hours for that cell.

It is TEDIOUS and quite boring as it takes forever *will feel like it" but if it saves the cells, it's worth it.
Never leave charger unattended for long and always verify the charger output voltage against what is seen at the cell terminals.

Hope it helps, Good Luck.,

 

[technerd1988]

How exactly does compressing the cells help with the gas? I'm not doubting your method because I've never tried it...but I do have this bloated 210ah cell here...its only puffed a bit on one side...its not part of the system anymore so I guess I should try...but I wonder why this works? I seen it other places too