Anyone buying these 305ah envision cells?
- Thread starter G00SE
- Start date
I missed this post.... “constrained “ is a much better term... but still needs to be expanded on..
houseofancients
Solar Wizard
Simple..
I use the mason box, and each cell had expansive "padding" in between them
... and if doing a simple spring type compression from the ends, most common would probably be 2rows of 8cells, how evenly is that pressure going to be distributed along the entire row of cells? These cells move quite a bit between 100% & 20% soc. I'd wager that simply applying the desired amount of spring tension at both ends of the row, does not equal the correct pressure amongst all the cells in that row. IMO, YMMV, $.02
Then there's this ... 7:15 if you like to ff
So the big question being how do we know if our cells were compressed initially to help squeeze out the “ bubbles “ before they were sold or distributed... ?
Top balance done on my 4s pack
My eve 105’s aint coming close after a top balance of same voltage measurement those are exactly the same
Now longer term testing wil bring more information
Capacity doesn’t matter for me if it’s around 300ah it’s fine for me
After discharging for 60seconds with 10A and loading back to 3.65 they stay pretty close togheter
My eve 105’s aint coming close after a top balance of same voltage measurement those are exactly the same
Now longer term testing wil bring more information
Capacity doesn’t matter for me if it’s around 300ah it’s fine for me
After discharging for 60seconds with 10A and loading back to 3.65 they stay pretty close togheter
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Zwy
Emperor Of Solar
Yeah, nice search results. If using a 'spring loaded' jig, has anyone calculated that a 304ah Eve weights over 12lbs. x 8pcs resulting in around 100lbs of cells that have to slide back and forth as the cells expand and contract? Even worse if using 16 per row. How has the floor of the compression jig been treated to accommodate for the cell's bottom having to walk back and forth? Sure, the outer few cells may have correct, or close to correct compression, but it's doubtful the inner cells will see those same numbers.
If it is a solid constraint, at what soc will the compression be correct, and for how many of the cells?
To compress, or not to compress, the cells are going to age out before they cycle out.
Zwy
Emperor Of Solar
I don't use a spring loaded jig. The search results are all that I have written regarding the subject, even my very first post in this forum was about cell compression.
You must think cells really move around/expand when charged/discharged under compression.
I'm not getting into that argument. One time someone posted a link to one of Andy's videos about cell capacity loss (trying to prove compression isn't needed) and I made the comment I wonder what capacity he would have lost if instead he had used cell compression in an actual side by side comparison. He never used an actual control group with side by side test so I considered the video just clickbait for views and nothing valid contained within.
Sure got the "Disciples of Andy" in an uproar.
My opinion is this, research the subject looking at manufacturer data/test conditions, decide what you think is best and apply it. Time will determine who was correct regarding that decision.
Zwy
Emperor Of Solar
No.
Zwy
Emperor Of Solar
Here is one data sheet for example of the EVE 280K V3. https://diysolarforum.com/resources/eve-lf280k-v3-pbri-lf280k-d06-01-datasheet.376/
42OhmsPA
What's in a title?
Looks like 18650 has 3 envision cells in stock as of a few minutes ago. I tried adding 17 to my cart for a quick check out but it reduced to 3 ?
LFP cells do expand and contract depending on state of charge. Here is data from A123 20Ah cells. They are 7.1mm thick so extrapolating to LF280K thickness we get 0.5mm total expansion per LF280K cell during 0 - 100% SOC cycle. Multiply by 16 cell stack = 8mm total stack swelling or +/-4mm if you compress them at 50% SOC. This is why compliant material is needed between cells to absorb this swelling without cells getting crushed.
SupraSPL
Solar Enthusiast
- Joined
- Aug 28, 2022
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- 223
I believe it is 2%. I've seen enough conflicting information that I don't bother to compress. Some packs I have secured in wooden enclosures and some secured with large plastic bands. I charge up to 3.55V about once a week. The only cells that I see with any bulging are the ones that came that way, acquired at a discount.
I interpreted @Zwy differently it seems. I don’t recall him denying expansion but his verbiage was “move during expansion”
What I deduced (and could very well be wrong) was that with 3mm foam inserts (or similar) if one is building their own battery fixture, then something like a threaded rod at a length matching the cell thickness + uncompressed inserts that any expansion would be addressed
If one was to follow his build thread….assembled with 3mm foam at 25% compression means each foam pad can still compress yet still provides constant “pressure”
The second part in my assumption was that with 10-12lbs PER prismatic cell, in a row of 8, that’s a lot of mass. And with .5mm of cell expansion (which would not be uniform nor would it happen at the base) it would be mighty challenging for a cell to physically move at all when even not compressed but simply “secured”
What I deduced (and could very well be wrong) was that with 3mm foam inserts (or similar) if one is building their own battery fixture, then something like a threaded rod at a length matching the cell thickness + uncompressed inserts that any expansion would be addressed
If one was to follow his build thread….assembled with 3mm foam at 25% compression means each foam pad can still compress yet still provides constant “pressure”
The second part in my assumption was that with 10-12lbs PER prismatic cell, in a row of 8, that’s a lot of mass. And with .5mm of cell expansion (which would not be uniform nor would it happen at the base) it would be mighty challenging for a cell to physically move at all when even not compressed but simply “secured”
