Compression material thoughts...

AW1090

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While waiting for my Lishen 272ah that will be in a 16s configuration, I’ve been thinking about all the “fixture” information and materials. Going through material to place in between cells, I came across this and wanted to get your guys’ thoughts.


It’s $3.47/linear foot. I’ll get three dividers out of each linear foot so 6ft would work. It’s a little grippy and won’t allow the cells to slip once compressed/fixed in place. Any thoughts are appreciated.

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AW1090

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Thanks! I’ve learned a lot and am still learning, but have gained a ton of knowledge from your input in the threads. Thank you.
 

jwelter99

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While waiting for my Lishen 272ah that will be in a 16s configuration, I’ve been thinking about all the “fixture” information and materials. Going through material to place in between cells, I came across this and wanted to get your guys’ thoughts.


It’s $3.47/linear foot. I’ll get three dividers out of each linear foot so 6ft would work. It’s a little grippy and won’t allow the cells to slip once compressed/fixed in place. Any thoughts are appreciated.

View attachment 44026View attachment 44027View attachment 44028

Just be aware that stuff can smell strongly so depending on where you have your battery that might be an issue.
 

Zwy

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Ya all make this way too hard, really. This thread describes what I used for foam material between cells. It was cheap too. I've included a photo of my compression fixture. Bottom plate is aluminum and held off the rods by small angle on each end, this allowed heating element below the tray. The bottom tray is exactly 308mm long. This figure was achieved by taking the length of 4 cells, adding in the 3/16" foam at 25% compression. This is the foam used,https://www.grainger.com/product/USA-SEALING-Water-Resistant-Closed-Cell-497F84 although I bought mine off ebay. This gave me 308mm for both sets of 4 cells. Rods on bottom are tightened to the bottom tray tight.

Next photo shows assembled pack. Note the pvc covers over the threaded rod. Inside each pvc cover is another nut at each end, set to 308mm length. Plate is tightened against these nuts so pack compression is 25% of the foam. I know that I have exactly 25% compression and the pack can't move. Only thing I would do different is install the threaded rod higher on the end plates, I almost did that but had this crazy idea it would help retain the cells which in hindsight wasn't needed.

As for the thickness of the plate, it's what I had laying around. The bottom tray was formed in a brake, I have access to anything I might need. One advantage of the thicker plate is it allowed tapping threads for holding the angle that holds up the bottom tray off the rods and it allowed the Daly BMS to be attached to the plate.

One more thing, double nut the threaded rods on the end or tig weld two flats on each side of a nut that is either welded or riveted on one end, this allow the rod to be held while the other end is tightened. In my case it was tight against the back wall so I tig welded retainers on the end. Everything is stacked in from one end.
 

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Diysolar123

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I just used 3/4" hardwood plywood with 3/8" threaded rod...
for the compression I used engineered springs with a known compression rate per mm/compression; I just measured the spring length as I tightened it so I knew the force applied.
 

Zwy

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I just used 3/4" hardwood plywood with 3/8" threaded rod...
for the compression I used engineered springs with a known compression rate per mm/compression; I just measured the spring length as I tightened it so I knew the force applied.
If it works for you. This was the original thread which I forgot to link. https://diysolarforum.com/threads/another-cell-compression-thread-this-time-about-foam.16537/

Note cell compression is between each cell and that is what the EV manufacturers are doing. I have the foam in between each cell and on the ends.

The problem with using the springs is you don't have compression of the cells in between, only cell face to cell face. None of the cells are perfectly flat plus anode damage could occur. There also reports of continuity between the cell face and terminals, possible short condition.
 

AW1090

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How are you getting even distribution of force along the sides of the cells? While I appreciate your input, I’m pretty sure you’ve over simplified and haven’t really thought it all through, but thank you for the input.

Also, I’m just asking for thoughts on the material and not all this other stuff.
 

HRTKD

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If I were to a compression frame for another set of cells, I would just use thin double sided tape. Maybe VHB, but probably any thin double sided tape would do. Minimal material between the cells and holds them in place just fine.
 

AW1090

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If I were to a compression frame for another set of cells, I would just use thin double sided tape. Maybe VHB, but probably any thin double sided tape would do. Minimal material between the cells and holds them in place just fine.

Yeah, this was the direction I was going with this material. It’s cheap, thin, but seems like just enough to hold them together and add a little cushion between the cells. I thought about vhb, but would like to be able to pull them apart if needed so that steered me away from the tape/adhesive route.
 

Heyjimmy911

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I used Yoshi Grill Matts between the cells, cut to size. They are made of PFTE and very thin. My goal was to prevent the thin blue plastic on my cells from rubbing against one another and eventually causing a short of some kind. Also it won't melt or soften when hot like other materials, for example, a plastic cutting board. I decided against a softer, thicker material between the cells and realize that cells are not perfectly flat. The failures I've seen tend to bulge in the center of the case, it seems to make sense as this (the center) is the weakest part of the case being farthest from the edges. The fixture prevents the de-lamination or separation of the battery layers over time. Limiting the center travel was good enough for me.

It's hard to argue with what EVs are doing though. With respect to force along the sides of the battery, I don't think this is necessary. The battery is assembled like a book and its the pages that need to be held together to prevent separation. I found the linked video below showing how one company makes their LiFePo4 packs. It's interesting to very few people.

I am not affiliated with Yoshi or with the battery manufacturing company in the video.



 

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Zwy

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How are you getting even distribution of force along the sides of the cells? While I appreciate your input, I’m pretty sure you’ve over simplified and haven’t really thought it all through, but thank you for the input.

Also, I’m just asking for thoughts on the material and not all this other stuff.
This was discussed at length in the compression threads. The short sides of the cells didn't matter.
 

HRTKD

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I used Yoshi Grill Matts between the cells, cut to size. They are made of PFTE and very thin. My goal was to prevent the thin blue plastic on my cells from rubbing against one another and eventually causing a short of some kind. Also it won't melt or soften when hot like other materials, for example, a plastic cutting board. I decided against a softer, thicker material between the cells and realize that cells are not perfectly flat. The failures I've seen tend to bulge in the center of the case, it seems to make sense as this (the center) is the weakest part of the case being farthest from the edges. The fixture prevents the de-lamination or separation of the battery layers over time. Limiting the center travel was good enough for me.

It's hard to argue with what EVs are doing though. With respect to force along the sides of the battery, I don't think this is necessary. The battery is assembled like a book and its the pages that need to be held together to prevent separation. I found the linked video below showing how one company makes their LiFePo4 packs. It's interesting to very few people.

I am not affiliated with Yoshi or with the battery manufacturing company in the video.




The Yoshi mat may not melt, but since it is a conductive material it certainly will transfer heat to the next cell. It seems to me that if you're going to put something between the cells, it might as well be a thermal barrier not a conductive material.
 

AW1090

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This was discussed at length in the compression threads. The short sides of the cells didn't matter.

I'm aware that the shorter sides aren't of concern, but was speaking of the distribution of force along the broad side of the cell. I've read your thread in the past and am aware of your design. I don't want to turn this into some sort of petty argument. I'm simply asking for thoughts on the material above as I can't seem to find a ton of material info for it. I'm glad you're happen with your fixture and hope it works well.
 

Zwy

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I'm aware that the shorter sides aren't of concern, but was speaking of the distribution of force along the broad side of the cell. I've read your thread in the past and am aware of your design. I don't want to turn this into some sort of petty argument. I'm simply asking for thoughts on the material above as I can't seem to find a ton of material info for it. I'm glad you're happen with your fixture and hope it works well.
What information would you like? At 25% compression, the foam exerts a force of 13 psi which is right where the cell manufacturers want it. This is across the face of the whole cell, which is what is desired. Using just plywood on each end with cells clamped together only applies force on high points of cells, usually where the anodes are located. This stresses the anode.

The cell can expand and contract the way it was designed to do using the foam and fixture I have. The specs for the material are listed here: https://www.grainger.com/product/USA-SEALING-Water-Resistant-Closed-Cell-497F84 Note at 25% compression, it exerts 13 psi.

I have a sheet on each plate and in between each cell. Photo shows pack assembled for testing, I added nuts on inside of plates to exact length the bottom plate is, along with a pvc conduit Schedule 40 to prevent shorts shown in second photo.

I think many are making too much out of this subject. When one reads what the EV manufacturers are doing plus use a little bit of engineering knowledge plus research suitable solutions, it isn't that hard.
 

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woodmtw

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What information would you like? At 25% compression, the foam exerts a force of 13 psi which is right where the cell manufacturers want it. This is across the face of the whole cell, which is what is desired. Using just plywood on each end with cells clamped together only applies force on high points of cells, usually where the anodes are located. This stresses the anode.

The cell can expand and contract the way it was designed to do using the foam and fixture I have. The specs for the material are listed here: https://www.grainger.com/product/USA-SEALING-Water-Resistant-Closed-Cell-497F84 Note at 25% compression, it exerts 13 psi.

I have a sheet on each plate and in between each cell. Photo shows pack assembled for testing, I added nuts on inside of plates to exact length the bottom plate is, along with a pvc conduit Schedule 40 to prevent shorts shown in second photo.

I think many are making too much out of this subject. When one reads what the EV manufacturers are doing plus use a little bit of engineering knowledge plus research suitable solutions, it isn't that hard.
Zwy, thank you for the USA-SEALING-Water-Resistant-Closed-Cell-497F84 recommendation. This seems like an elegant, moderate-cost solution for my 8s 24v LiFePo4 272Ah cells. I bought two 12"x24" 3/16" sheets (adhesive on one side) on eBay for under $50 shipped. Thank you for sharing!
 

Zwy

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Zwy, thank you for the USA-SEALING-Water-Resistant-Closed-Cell-497F84 recommendation. This seems like an elegant, moderate-cost solution for my 8s 24v LiFePo4 272Ah cells. I bought two 12"x24" 3/16" sheets (adhesive on one side) on eBay for under $50 shipped. Thank you for sharing!
I bought mine from the same place, I think it took me 2.5 sheets of it to cover my cells and the ends with the side by side packs. I did add some left over in between the cells, mainly just to insulate them from each other. I bought mine from this seller. https://www.ebay.com/str/buyfromzoro?_trksid=p2047675.l2563
 

NMNeil

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Zwy

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Options for electrically insulated dividers, all readily available at your local store and cheap.
Do they provide the necessary psi when compressed for cell compression? Doubt it.
 

NMNeil

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Do they provide the necessary psi when compressed for cell compression? Doubt it.
Check the spec sheet :giggle:
I'm just showing the possible cheap solutions. I don't know if there is any product made specifically for this application, so I just look around for things that would work.
 
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