Right but then it’s the expansion of the cells that makes the psi continue to rise against the fixed structure as SOC rises. As I said using the foam and fixed structure is an option and most likely will be fine.
Why 15mm expansion range? How many cells do you plan to stack in one box?
There’s a link for poron foam earlier in this thread. @rhino shared it
Why 15mm expansion range? How many cells do you plan to stack in one box?
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I used one 0.25" thick sheet per four cells. I built a 4S battery with one sheet, and four 8S batteries with two sheets each. The 8S batteries are combined as 16S2P. I built them as 8S because I can barely lift eight cells at a time, and I wanted to be able to lift each pack out of my containment box for any maintenance as needed. The packs allow the same braided bus bar to fit across the frames so that all bus bars are the same for the 16S batteries.
Here is a photo of two of the packs under top balance. You can see the foam at each end of each frame. Expansion of new cells from 30% to 100% SOC when charged at 0.1C or less was negligible.
View attachment 112514
0.1C is a reference to charge current, so it is the same for all cells in series. The expansion is the same per cell.
Not exactly
Is there not a correct psi range throughout the entire SOC. I have read that to be 12-17psi. If at 30% SOC the psi is set to 12 in a rigid/fixed structure. then as the SOC increases the pressure can rise above 17psi, which is worse than no compression at all from what I have read.
Apparently not.
I used these, they are perfect for a four cell stack.
Like I said (pretty clearly, I thought) above, roughly 0.1C. The 16 cells were in series at the time. Expansion was negligible, which means that the force didn't change much at all from 30% to 100% SOC. I know this because the force of the Poron foam is correlated to the distance it is compressed. The thickness of the foam didn't really change, so neither did the pressure.
Huh? The pressure is uniform inside the box. No cell has less pressure than any other cell. The foam pushes against the cells just as hard as the cells push against the foam. Honest. The sum of the forces inside the enclosure is zero. I know this because nothing inside the box is moving.
Compression is now apparently clarified in the datasheets, so it may be best to not cling to the information in older datasheets. They now mention a compression force range, which (for 230 Ah cells anyway) happens to equate to about 3kN (11.7 PSI) to 5kN (19.6 PSI). The implication is that this compression is the normal range of a cell taken from 30% SOC at 11.7 PSI to 100% SOC in a hard fixture (no springs or foam). Under normal conditions, the force should not exceed 7kN (27.5 PSI). It can exceed that if internal damage or cell leakage occurs.
Excuse me for asking you to explain further........
Imo if using foam the pressure can’t be perfectly uniform for each cell if there isn’t foam between each cell. As the cells expand the cells that do not have foam against them would have more pressure due to being against a harder surface which is the wall of the cell it’s next to.. if you didn’t have foam at the ends and instead had the cells against a hard end plate then the end cells outside wall would have similar pressure to the rest of the cells that are against hard cells.. of course then you wouldn’t have the expansion room the foam allows.. again if nothing in your box is moving and the foams thickness isn’t varying then why have the foam at all? Again if nothing is moving at all in you4 box I’d think it’s over compressed.. and again most importantly, that all might not matter at all and is most likely fine for a low power demand solar setup but who am I to say, I’m simply trying to figure all this out. Ima do springs because it can’t hurt
