Compress or Not Compress Bloated Cells?

PatM

New Member
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Sep 13, 2020
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4
Received my second shipment of Catyl 302/310ah cells from Basen. Cells were all quite bloated. Almost a 1/4" of space between cells. I top balanced to 3.58 and noticed the cells expanded another 1/8" or more. Went to put them in series for capacity test and couldn't fit the bus bars without canting the cells. Ran capacity test and got 321ah. I was disappointed at getting bloated cells, then delighted at getting great capacity. To top that off, after capacity testing, the cells contracted to almost flat.
So the big question is, to compress while they are almost flat and then charge them and hope they don't blow the pressure relief. Would be compressing with 1/4" aluminum plate like I did with previous non-bloated cells.
 

Groscout

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1/4-3/8” between cells? That sounds like a lot for a low c top balance.

I’m curious what your supplier would say about the bulging. If your suppler recommends compression as a solution I would recommend this thread for close review.

I just ordered constant rate springs for my build and am hoping that solution goes well.
 

bobdelso

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Aug 11, 2020
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If they are already swollen, compressing them is not a good idea. Compressing them can cause an internal short.

Use some flexible bus bars and leave them lightly wrapped with tape or something stretchy.
 

Horsefly

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LiFePO4 cells expand with SoC. So when fully charged, they will "bloat" a bit. I can't judge your cells.

I'm not really subscribed to the compression mania that took hold here a few months back. I think it is good to put your cells in some sort of structure that holds them somewhat ridged, and that prevents them bulging too much, if that bulging will eventually compromise the integrity of the aluminum case.

My current theory - with no science or endorsement of the cell manufacturers - is to build a structure that keeps the cells from straining or breaking the connections between your cells with regard to the bus bars. If you have a method to tighten or loosen this structure (e.g. threaded rods) tighten them only to the point that it is difficult to move the cells with your fingers, but not so much that you can pick up the whole thing and no cells slip down.

Not particularly scientific. I think the risk of over-compressing cells is not insignificant. If compressing them "perfectly" extends their life from 2500 cycles to 3500 cycles, I don't care for two reasons: (1) I'll be dead, and (2) LiFePO4 will be "yesterday's technology". I'm counting on my kids replacing them at that point anyway. :p
 

Gazoo

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1/4-3/8” between cells? That sounds like a lot for a low c top balance.
C rates have nothing to do with expansion. I use very low C rates to charge my 8 EVE 280ah cells and they still expand. But yes 1/4 to 3/8 expansion is more than the norm.

I’m curious what your supplier would say about the bulging. If your suppler recommends compression as a solution I would recommend this thread for close review.
Most suppliers don't know beans regarding many things including compression. I would be curious what the manufacturer has to say.

I just ordered constant rate springs for my build and am hoping that solution goes well.
I hope it goes well for you too. I decided not to get into the weeds regarding compression. It is important to keep in mind too much compression is worse than no compression.
 

Substrate

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Apr 28, 2021
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The Urban Myth about bloating is normal (even a little bit) lives on!

They are NOT supposed to bloat. Use reverse logic:

"Would any reputable manufacturer even offer rigid bus-bar links that when bloating occurs, which applies a vertical-force like a crowbar on your cell terminals when the loose bank starts to go into accordion mode?"

If bloating or breathing were normal, wouldn't ALL manufacturers warn against using inflexible or even semi-rigid busbar links, and promote braid or individual flexible cabling instead?

Like they say there are 3 things you can't avoid in life: Death, Taxes, and Battery Salesman. :)

Be smart. Compress the bank. Like the pros do.
 

bobdelso

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Joined
Aug 11, 2020
Messages
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The Urban Myth about bloating is normal (even a little bit) lives on!

They are NOT supposed to bloat. Use reverse logic:

"Would any reputable manufacturer even offer rigid bus-bar links that when bloating occurs, which applies a vertical-force like a crowbar on your cell terminals when the loose bank starts to go into accordion mode?"

If bloating or breathing were normal, wouldn't ALL manufacturers warn against using inflexible or even semi-rigid busbar links, and promote braid or individual flexible cabling instead?

Like they say there are 3 things you can't avoid in life: Death, Taxes, and Battery Salesman. :)

Be smart. Compress the bank. Like the pros do.
Op likely got grade b cells that were rejected. Those cells swell beyond the allowed amount.

Compress good, grade a cells that haven't swollen

I wouldn't compress swollen cells as you can't undo that damage
 
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