Around 40% SOC.
Anyone buying these 305ah envision cells?
- Thread starter G00SE
- Start date
Brucey
Velcro Man
Most builds I've seen seem to use solid separators like plastic sheets/cutting boards etc. using a deflecting foam may not be what the manufacturers had in mind.
Most Chinese battery module assemblers don't seem to care about proper battery engineering. You get what you pay for.
Zwy
Emperor Of Solar
Back in my very first post in these forums, I linked the use of foam by OE car manufacturers for battery packs.
As for what the battery manufacturers specify, they only give the jig fixture and it's force and the measurement for cell expansion.
I'll still build my packs with foam with a fixture. I've torn these packs down after use, the cells retained the original shape. I have not had any failures. I run a 24V pack in my truck camper, currently has over 8K miles on that pack and works as good as the day I installed it with no degradation in cell performance.
Max compression force of 10000n before damage, rec. 30000-7000n compression force, mentions swelling force changing with soc, but found no information actual mm of expansion/contraction. Some where, data sheet or white paper, I have seen mention of a cell's expansion/contraction. It was surprising how much movement x8 of those cells generated.
ArthurEld
Solar Wizard
I find the bottoms to be fatter than the tops. Like the jelly roll sags from gravity.
So I torque the bottom to the high end of the torque range and torque the top to the low end of the torque range.
I am fairly sure they change shape slightly after a few cycles while constrained.
So I torque the bottom to the high end of the torque range and torque the top to the low end of the torque range.
I am fairly sure they change shape slightly after a few cycles while constrained.
Sorry for the newb post, and maybe it's covered in 22 pages of thread, but I got my 4 cells last week, and I am trying to decide if the amount of bulge is both normal and safe. These are my first batteries. My first capacity test shows at least 304Ah (only top balanced to 3.6V instead of 3.65V, not sure what difference that makes, discharged to 2.5v). I did the test at around 60A, and I was also able to pull ~200A without issue. They are maintaining balance in the limited cycling I've done so far. Functionally they seem fine.
I'm not sure what the standard method for measuring bulge is, but when I put them next to each other, some combinations have as much as 5mm gap at the top, meaning 2.5mm bulge on each (or so). Assuming equal bulge on both sides, that's almost 7% increase in width.
Are these safe to use? I've emailed 18650batterystore twice with no response. Do I need to pull out the big guns with them and get a refund?
I'm not sure what the standard method for measuring bulge is, but when I put them next to each other, some combinations have as much as 5mm gap at the top, meaning 2.5mm bulge on each (or so). Assuming equal bulge on both sides, that's almost 7% increase in width.
Are these safe to use? I've emailed 18650batterystore twice with no response. Do I need to pull out the big guns with them and get a refund?
Are those cells grade B ? New cells should be flat. My 105Ah cells from them had no gap when stacked. They developed small barely noticeable bulge after few full cycles.
Yes, the grade B AESC cells in the OP. Also, I think they were flatter when I pulled them out of the box. Didn't notice this amount of bulging until after starting the charge cycle.
In that case you probably should not compress them unless you can guarantee even compression force across entire side of cell. With 2.5mm bulge you would need very think foam sheet between cells. Compressing to 5% foam deflection on the corners (around 2 - 5 psi) would produce 60% deflection (45psi) in the middle with 10mm foam sheet. You would need 20mm thick sheet or almost 1 inch to keep compression force under 20 psi in the middle.
Thanks for the info -- I won't plan on compressing them, and from what I gather in the most recent couple of pages is that could be just fine for battery longevity. A link describing compression is helpful would be appreciated, given the youtube link saying it's not a couple of pages back.
Should the swelling be a cause for concern?
Should the swelling be a cause for concern?
Probably not but I am not sure. Your likely have previously used cells. I would monitor each cell temperature and self discharge to stop using them if they deviate from normal.
Search for Document #:493005-002 Battery Pack Design, Validation, and. Assembly Guide using A123 Systems.
Brucey
Velcro Man
Did you have them clamped?
Brucey
Velcro Man
No. Just taped together using packing tape. I did not fully cycle them to limit cell bulging until I can properly compress them. Need to order some 1/2" alum plate for that.
This seems relevant to my concern:
Not sure what that means to start at 7% thicker though.
My 2 year old LF105 bulged about 0.6mm on average. Less than 10 partial cycles. They been mostly sitting at 13.6V as ballast battery for my 12V loads powered by DC-DC converter. When I bought them new they were perfectly flat with no light visible between cells. Corner cell in 2nd image looks warped due to lens distortion in my phone camera.
These are LF280 cells, from 2018, in use 24/7 since 2020 when I got them:
diysolarforum.com
No bloating, no bulging. Still flat as ever. Also note: no spacers/foam/compliant pad between them. Don't know if I will change that yet with the up and coming 30kWh upgrade.
LiFePO4 cells in use since 2020. Bloating? Capacity?
As some of you may know, I'm in the process of moving my batteries into a new enclosure. Reasons: it's more organized, space is better optimized, and I can add more batteries more easily later if needed. This is the first time I took these apart since I built them somewhere early 2020. I bought...
diysolarforum.com
No bloating, no bulging. Still flat as ever. Also note: no spacers/foam/compliant pad between them. Don't know if I will change that yet with the up and coming 30kWh upgrade.
That's because you had them clamped since they were new. But clamping them without compliant material risks damaging them long term as they age.
Yeah, I agree - but those threaded bars and wood should offer quite some flex. In any case, let's see if I change it with the upgrade.
ArthurEld
Solar Wizard
The cells bulge the most when they are fully charged.
I use a compression fixture.
And I set the compression when the cells are fully charged.
My cells haven't had anything between them either. That wasn't a thing a few years ago. Since my new cases come with the spacers, I will use them.
I use a compression fixture.
And I set the compression when the cells are fully charged.
My cells haven't had anything between them either. That wasn't a thing a few years ago. Since my new cases come with the spacers, I will use them.
blstringham
New Member
I ordered 32 of these and built 2*16s batteries. They are down to $75 each now and are usually out of stock within a few days. Both my batteries are working exceptionally. No problems with shipping. Packaging was top notch. The batteries are a bit swollen in the middle on the broad side but this can be expected and is fine. Lifepo4 will expand and contract no matter how perfectly you compress your batteries.
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