Another Cell Compression Thread, this time about foam

[Hedges]

Yes, two sheets for eight cells. I will probably put one on each end, but I don't think it matters much.

Busbars and distance between terminals?
If the goal is to let each cell expand and contract, ideally they do that without moving terminals relative to each other. For that I would think rubber sheets between all cells, and 1/2 thickness at each end.
Unless your busbars are flexible.

 

[justgary]

Busbars and distance between terminals?
If the goal is to let each cell expand and contract, ideally they do that without moving terminals relative to each other. For that I would think rubber sheets between all cells, and 1/2 thickness at each end.
Unless your busbars are flexible.

Flexible busbars and hard separator sheets from Docan.

The goal is to allow expansion while maintaining the specified compression of 8 to 18 PSI. Falling short on the low end is apparently far better than exceeding the high end, so this should work out well.

 

[justgary]

OK, so I got the first compression frame completed. This is the 4S 230Ah pack with one 1/4" sheet of Poron 50-15250 foam as a compressing agent. You can see the separator sheets from Docan sticking up between the cells. The sides and bottoms of the cells have extra material to keep from somehow shorting the cells.

The end caps are 1/4" aluminum and the straps are 1/8" aluminum, all held together with 4-40 flat head screws. My bar clamps were barely strong enough to compress the foam to line up the screw holes. Before you ask, yes, 18 screws on each end will easily hold the ~660 pound maximum force.

The JBD 200A BMS fits nicely on the side. Time to begin a top balance on these four cells!

 

[Seplos Chris Ren]

Is the foam mentioned in the SEPLOS battery? 2mm in depth.

 

[justgary]

Is the foam mentioned in the SEPLOS battery? 2mm in depth.

What is the force profile of the stack of foam used in the Seplos battery?

 

[Gette]

@justgary "OK, so I bought the Poron 50-15250 sheet from McMaster."

Do you happen to still have a link or the McMaster part number or sku for what you bought?

I went there and searched around but could not narrow it down enough to find anything "50-15250"?

Thank you sir!
Geo

 

[Zwy]

Poron 50-15250 - Google Search

Might need to put 4701 as a prefix

 

[Gette]

Poron 50-15250 - Google Search

Might need to put 4701 as a prefix

Thanks @Zwy.

Regarding search, I meant specifically in McMaster. 642 Products. lol

Yes I've been looking outside of McMaster. I did see the 4701 prefix.

I'll find something. No Big Deal.

 

[justgary]

@justgary "OK, so I bought the Poron 50-15250 sheet from McMaster."

Do you happen to still have a link or the McMaster part number or sku for what you bought?

I went there and searched around but could not narrow it down enough to find anything "50-15250"?

Thank you sir!
Geo

My PO shows 86375K234 as the SKU I bought.

 

[Gette]

My PO shows 86375K234 as the SKU I bought.

Thank you sir!

 

[Gette]

View attachment 99519

View attachment 99520

That is a thing of beauty!
Well done sir.

 

[justgary]

That is a thing of beauty!
Well done sir.

Thanks. I might be inclined to just use a rigid frame if I did it again. Getting the force correct in a rigid frame seems awfully pesky though, and it was relatively easy for me to calculate the distance required to get the force with the foam.

Photos of the 16S batteries are floating around here somewhere. I still don't have them in their final resting place due to delays on crimping the cables needed to hook everything up (as 16S2P). Soon....

 

[justgary]

Oh, yeah, here is one of them. The two BMSs came with 4 gauge aluminum cables. Those are getting swapped to 2/0 with everything else.

 

[Capt Bill]

Very Good Looking Set Up for LiFePO4s. I might have consider that if I had access to reasonably priced flex bars when I did mine. I personally think this compression is more important in EV applications, and have been concerned about internal LiFePO4 terminal damage when done with solid bus bars (as battery sides change dimensions with SOC with various Amps in and out). ... I used this other way wo compression, ... using 90 cm Bus Bars (Width: 20mm, Thickness: 2.0mm, 2-Hole distance: 72mm, Length: 90mm) ... my 3 x 24v 280Ah EVE LiFePO4s Battery Banks are currently assembled with 1/4" spacing between each battery side via using these 72mm Copper Bus Bars - Nickel Plated High Current Flow 2mm Thickness for 272Ah 280Ah 302Ah 310Ah Battery Terminal Connects https://www.aliexpress.us/item/3256...tewayAdapt=glo2usa4itemAdapt&_randl_shipto=US

 

[Ron-ski]

OK, so I bought the Poron 50-15250 sheet from McMaster.

<snip>

So, it seems that a stack of eight cells with two sheets of foam can expand up to 8X0.5mm = 4mm (~0.160") and still be below 18 PSI if I start with a 0.2" total (0.1" per sheet) displacement in the foam. That should give me a range of about 7.5 to 18 PSI over the expected expansion of the cells. It also seems that my 4S battery will start at about 5 PSI, not 9 PSI. Oh, well.

Enjoy!

Your battery pack above looks fabulous.

I actually managed to find this foam in the UK, but what did you use between the cells?

 

[justgary]

Your battery pack above looks fabulous.

I actually managed to find this foam in the UK, but what did you use between the cells?

Thanks.

Docan sent fiberglass separators with the cells.

 

[meetyg]

I use 1mm thick EVA foam (similar to Seplos kits) between the cell.

 

[Honuz]

Your battery pack above looks fabulous.

I actually managed to find this foam in the UK, but what did you use between the cells?

I use whatever foam i got, on the EVE pack i used 3mm foam sheets.
Box is builded with HPL material.

 

[dielectric]

Interesting Reads ... In looking at how those researchers are talking allot about EV batteries/ I am wondering if compression of LiFePO4 are much more important for Electric Vehicles as compared to stationary home solar battery banks ... Just wondering out loud; / ... while thinking if I eventually compress my 16 280Ah LiFePO4 cells on my next battery pack update, I would also want flexible bus bars. I am still wondering about real life benefits on my stationary cells that have very slight wave on sides / showing me my LiFePO4 battery cells sides are not exactly flat planned.

from interesting reads: " ... research indicates that optimal battery lifespan occurs when a moderate amount of pressure is applied to ensure electrical and thermal connections while the battery ‘breathes’ during its discharge and recharge cycles. ... help prevent delamination and deformation in pouch-type, actively-cooled, Li-ion battery packs, thereby keeping more EVs and hybrids on the road every day."

I know old thread...
But I don't see any answers to this. This mechanical stress with rigid bars connecting terminals is the reason I decided to not compress at all. In stationary application air gap seems the best way to eliminate tension on battery studs. When I read "pressure" I don't interpret that as a fixed unyielding wall. I'd have to build rods with springs otherwise we'd get very variable pressure.
And if there are springs/cushions and cells expand rigid connectors are an issue.

Have you found an answer to this? How did you decide to build your pack?

 

[Ron-ski]

Have you found an answer to this? How did you decide to build your pack?

I'm aiming to do similar to @justgary and I'll be using laminated flexible bus bars. Was going to use springs, but they will protrude from the end of my rack.