Overvoltage damage to LiFePO4 cells?

[tduncklee]

I've searched but have not found the answer. I've been capacity testing each of my 64 100ah cells. When charging them back up to top balance, I accidentally brought about 50 of them up to 4.4V. Have I damaged my expensive cells? If so, how badly? These are the Fortune cells Will recommends.

 

[snoobler]

More likely than not. Unknown. Any swelling is an indication of likely damage.

You'll have to re-test them and compare them to their prior results or at least to the results of the ones that weren't overcharged.

Anything above 4.2 is potentially catastrophic. Anything above 3.65 is not recommended.

 

[tduncklee]

Sounds like I've made a very expensive mistake. ?
Thank you.

 

[snoobler]

You won't know until you test.

 

[BarkingSpider]

You may be suprised, some quality LifePo4 cells like A123 (used in Dewalt tools and hospitals) can take an amazing amount of abuse. You dont even need to use a BMS with them for small batteries, and you can charge them with a standard car charger if you need to.

If the final few volts you used were low amperage, and it was not for too long, your probably fine. They are not like Li—on cells that burst into flames when they get over charged.

My test battery made of A123 cells have been really low and really high at times and still work like new.
Remember, 4.2v is still within spec for LifePO4.

Time will tell, but if it was only briefly, there is no swelling and they didnt get hot, your probably fine.

 

[tduncklee]

You may be suprised, some quality LifePo4 cells like A123 (used in Dewalt tools and hospitals) take can an amazing amount of abuse, you dont really need a BMS with them for small batteries, and you can charge them with a standard car charger if you need to.

If the final few volts you used were low amperage, and it was not for too long, your probably fine. They are not like Li—on cells that burst into flames when they get over charged.

My test battery made of A123 cells have been really low and really high at times and still work like new.
Remember, 4.2v is still within spec for LifePO4.

Time will tell, but if it was only briefly, there is no swelling and they didnt get hot, your probably fine.

No swelling and they did not even get warm. The 40 amp supply was spread out over 40 cells in parallel so they got about 1 amp per cell. I've recorded the capacity of each individual cell so I guess I'm doing another capacity test on them. Two additional weeks of testing... ?

 

[Bob B]

The most common and sometimes devastating mistake people make when doing the initial top balance is incorrectly adjusting the charge voltage ...... The power supply voltage must be adjusted before it is connected to the battery.

When the power supply is connected to the battery the voltage will drop ... and as the battery voltage comes up and the current drops off, the power supply voltage will increase. If the supply was adjusted after connecting to the battery there is no way to know where it will end up.

I'm just posting this in case that is what happened .... and you know how to keep it from happening again.

 

[Sojourner1]

There was a time when 4.2+ vpc was commonly used but eventually it was learned that damage to the cells was occurring. Overtime the vpc was lowered for longevity and still have full use of the power stored.

If the cells aren't showing bloat you might have dodged a bullet.

 

[tduncklee]

The most common and sometimes devastating mistake people make when doing the initial top balance is incorrectly adjusting the charge voltage ...... The power supply voltage must be adjusted before it is connected to the battery.

When the power supply is connected to the battery the voltage will drop ... and as the battery voltage comes up and the current drops off, the power supply voltage will increase. If the supply was adjusted after connecting to the battery there is no way to know where it will end up.

I'm just posting this in case that is what happened .... and you know how to keep it from happening again.

Agreed. However, Impatience caused me to crank it up to speed things up. With 64 cells, I've already been at this for nearly a month and still far from done. I thought I was watching it closely but apparently not. I think I'll build a single cell BMS to disconnect the charger when it hits 3.65 just for safety.

 

[tduncklee]

There was a time when 4.2+ vpc was commonly used but eventually it was learned that damage to the cells was occurring. Overtime the vpc was lowered for longevity and still have full use of the power stored.

If the cells aren't showing bloat you might have dodged a bullet.

Thank you so much for the words of encouragement!

 

[MadMax03]

I think I'll build a single cell BMS to disconnect the charger when it hits 3.65 just for safety.

Boom. Done. No more problems.

 

[Smokin]

You left out Smoke
see 50:00 overcharging the little Puppy.