Overcharged cells on balancing… how bad is it?

[Supervstech]

Member @kromc5
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kromc5​

Solar Enthusiast​

Today at 7:27 PM
Had an emergency with a client and rush up to help, took longer to remedy and lost track of time. Rushed back down and the bank of 4 were at 4.394. Was able to bleed them back down to 3.60 in about 5 minutes. No swelling and just barely warm to the touch. I wonder if they pose any chances of fire, I will test them but even if they test well should they not be used? I started to post in my main thread but never get many responses, any insight you may have would be helpful.

Thank you

 

[Supervstech]

I advised he connect the BMS, then discharge them for a day or so slowly with a usb charger, or an inverter running with no load…
Any advice for the guy?

 

[MisterSandals]

Any advice for the guy?

Permanently add safety features (?properly configured and connected BMS?) so it doesn’t happen again?

I do not have personal overcharge experience but from the many threads about overcharging, I suspect his cells are fine and safe to use.
But watching the closely for first discharge and recharge is a good safety measure.

 

[OffGridInTheCity]

One of the risks with 18650 cells is 'dendrite formation' due to abuse. Abuse might include over-charging, denting, extreme discharge, temps?, ... Dendrites are spikes that form inside the cell and can cause *shorting* with implication of fire with implication of cascading fire thru the pack.

Does LifePo4 suffer from dendrite creation because of 'abuse' / overcharging in this case? If so, are LifePo4 subject to shorting out like 18650 - from what I read they are *much* safer - but this thread gives me a specific occurrence to ask about.

 

[toms]

Not much help after the damage is done - i’ve seen LiFePO4 cells that suffer dendrite failure - it is quite sudden but unspectacular.

Best advice i can give is if he gets another pack - don’t parallel top balance.

 

[DLTooley]

Doing capacity and IR tests is probably all you can do to evaluate at this point. Longevity might be effected, but there’s nothing you can do about that, consider it as Schrödinger’s cat drinking the spilt milk of your battery pack....

Reporting any results here would decrease the uncertainty for the community here. TIA.