Bloated LiFePO4 Cell Configuration

[Will Prowse]

This configuration was suggested by my viewers, and it works great! None of the cells are touching each other, so they can expand or contract as they please. I will cycle these as long as I can, and report back.

Would love to hear your thoughts. Previously, the bloating was so severe that the terminals were getting a lot of stress. This seems to be ideal.

 

[kenryan]

So I thought you previously said compression was best to eliminate expansion. Now you seem to be saying the exact opposite -- allow unlimited expansion.

 

[Will Prowse]

I said I need to limit movement from expansion (usually with compression) to avoid damage of the terminal. I don't mind the actual expansion at all. I am not trying to increase the cycle life as some forum members here aim to accomplish. I have zero interest in doing that.

 

[kenryan]

Thanks Will. That clarifies things for me. It also suggests that there would be more elegant ways to address the expansion issue than trying to stop it with compression.

 

[BMcL]

Yes, the "off-grid garage" guy also doubts compression is worth the trouble.
I wonder if compression could make a battery failure much worse by melting adjacent batteries ?
I like the idea of separating them some.
Whatever life you gain by compressing them ; say an extra 2 years (10 instead of 8)
in that time the LifeP04 batteries could be replaced by better technology.

 

[feo]

Super interested in seeing how much useful life you get out of B grade cells.

90% capacity, unknown longevity for 50% price. Hmm, still too much of a gamble for me (the numbers are inaccurate, but you get the point)

Once we know how long these last we can complete the equation.

There is also the hidden cost of safety.

Looking forward to long term reports!

 

[BMcL]

Super interested in seeing how much useful life you get out of B grade cells.

If they lasted only 2000 cycles, that could be 6-7 years.
I'm waiting on a batch of 16 280AH cells and hope they are decent.

 

[Supervstech]

Ha… slight slip of the tongue there will! Important safety tip… when moving bodies, have a TRUSTED assistant…

 

[wattmatters]

Spare a thought for me as I am just about to move some bodies, um batteries!

I'm about to reconfigure my battery set up including adding a second bank in parallel.
Mine are SLA units and they are 60kg (132lbs) a piece. I have 8 of them. Lead is heavy!

One day I'll go LiFePO4 but for now these are much cheaper and do what I need (sit there on float and be ready for backup supply).

As to Will's batteries, I guess some form of plastic or timber box cover which can slide over the bank from the end opposite to where the BMS's are.

 

[Zwy]

I said I need to limit movement from expansion (usually with compression) to avoid damage of the terminal. I don't mind the actual expansion at all. I am not trying to increase the cycle life as some forum members here aim to accomplish. I have zero interest in doing that.

You forgot RV/mobile applications. One should utilize compression for those applications simply to reduce terminal damage from vibration.

 

[Substrate]

Hi, it's your paranoid shop-teacher here.

UNSAFE. Allowing a cell to bloat and breathe defeats the whole purpose of the safety vent, which is manufactured / calibrated to open up at a specific psi and allow for venting in a *controlled* manner in case of a catastrophic event.

That catastrophic event is usually overcharge from some sort of failure, or as you've indicated, if that upper conductive shelf comes down on the bare terminals. Maybe cut up some plexiglass sheet for a top cover.

When the cells are allowed to bloat, if a catastrophic event occurs, the swollen cells have defeated the calibrated psi opening of the vent, and if the event continues, instead of the vent opening, a major case failure of shrapnel, or even a cell terminal can be blown off like a bullet. You don't want to be around that.

Heck, even lead-acid agm's come with those calibrated vents. And of course all the cylindricals of any li-ion chemistry.

< Bell rings > Ok you kids, get outta' here, I gotta' another class coming in....