How do you protect your good cells from damage from your crappy cells "running out" nearby?

[Luk88]

So I have some quantity of rather bad LFP cells I'm considering using.

If I do they'll live on the same battery rack (a shelf above or below my good cells) - for those that saw my vertical "fixtures" I'm switching to a horizontal arrangement soon.

Any of you using cells that can turn bad quick has some useful protection method?

I realise the best would be to encase them in an air tight container and vent out. But that is more investment than the crappy cells are worth.

So, as this section is focused in second life batteries.What would you do!

 

[sunshine_eggo]

How do you protect your good cells from damage from your crappy cells "running out" nearby?​

You don't use them.

 

[Nobodybusiness]

So I have some quantity of rather bad LFP cells I'm considering using.

If I do they'll live on the same battery rack (a shelf above or below my good cells) - for those that saw my vertical "fixtures" I'm switching to a horizontal arrangement soon.

Any of you using cells that can turn bad quick has some useful protection method?

I realise the best would be to encase them in an air tight container and vent out. But that is more investment than the crappy cells are worth.

So, as this section is focused in second life batteries.What would you do!

Define bad…

 

[Luk88]

How do you protect your good cells from damage from your crappy cells "running out" nearby?​

You don't use them.

We are in the "second life" cells section...

LFP is not like LiPo or even LiIon that burst in flames during thermal runaway. I've read a research article that described how they measured temperatures, gas compositions etc of lifepo cells during runaway and later fire. They don't start producing hydrogen until well into "proper fire" territory (450 Celsius if I remember correctly) and during your typical failure unless the electrolyte vapour ignites they don't exceed ~230 Celsius. So it seems doable to protect good cells from that.

Define bad…

Let's make it simpke and use the (pick your own)manufacturer datasheet "end of life" description.

So at least one of (perhaps all of):
- less than 70% usable capacity
- exceeds IR spec (AC & DC)
- doesn't meet dimensional spec (swollen)

 

[sunshine_eggo]

Second life is about repurposing cells that have reached their useful life in their application and then re-using them in a far less demanding application.

It's not about taking ragged out cells that are risky and setting fires.

 

[toms]

I have not seen any LiFePO4 failure mode that will damage adjacent cells in a series arrangement. Use a BMS that will disconnect load from bank when any cell is out of range, if your bank doesn’t deliver your desired capacity replace weakest cell until it does.

EVERY single pack will eventually encounter this situation. Brand new fancy perfectly matched cells will be in the same situation 15 or so years from now. No need to worry, one cold morning your power will go out when you put the toaster on, the pack won’t burst into flames..