Compression material thoughts...
- Thread starter AW1090
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Zwy
Solar Wizard
Instead of using material like that, you should just leave the cells loose with no compression. Just because it is cheap and one might think it is beneficial doesn't mean it is.Check the spec sheet
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.
If you look thru the archives regarding cell compression, (it will take hours of reading), you will find engineers from the cell manufacturers had a specific requirement for cell compression. If it is too tight, then it will degrade cycle life more than just leaving the cells loose.
I researched what EV manufacturers are doing regarding prismatic cells. I posted the link in the original thread. You obviously didn't read the material and what that supplier had for information.
If you're not willing to put forth the effort to research and understand exactly what they have, I can't help you. Ignorance can be bliss, I have presented what my research indicated was the best solution for cell compression without spending a huge amount of money. Doesn't make sense to spend around $500 USD for 4 cells, wait over a month to get them but want to be a tight ass when it comes to materials for cell compression. You aren't taking the subject seriously and would be better off leaving cells loose.
Lay cells on their sides and use body filler(Bondo) and screed off flat and level, like concrete, to fill the valley. I believe somebody elsewhere else mentioned epoxy. Probably the same idea. Then use additional whatever if deemed necessary.
Zwy
Solar Wizard
How do the cells expand and contract as SOC changes?
I think NMNeil was looking at something to provide extra electrical insulation between the cells. In my opinion, installing insulators between the cells and flexible interconnects to prevent terminal stress are a good idea if nothing more than for peace of mind and extra assurance.
Regarding cell compression your idea isn't bad although I question how well the firmness of the foam will hold up over time....I don't know. And at $26.75 plus shipping I think I would use springs instead.
I read through everything EVE's engineer suggested and then concluded the only way to ensure proper long term PSI sustained compression is to use springs, although I am not going to go down that road. I will be more than happy to get 2000+ cycles from the cells and still have 80% capacity.
How is that going to work? How would you secure the battery?
I compressed my cells with plywood and threaded rod. The compression frame is then screwed into the floor. Any vibration would be transmitted through the bracket used to secure the battery to the floor. Foam under the cells wouldn't help. I do have a thin layer of foam under the cells, but it's to get a small amount of insulation (temperature), not for vibration. The foam is just under the cells, not under the compression frame.
My RV trailer goes down BLM and Forest Service roads. I'm not seeing any issues with the bus bars or cable lugs. I'm not using lock washers or thread locker on the terminal screws. I checked my screws recently and found none of them loose.
BretS
New Member
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- Mar 30, 2021
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I have a ton of Floormuffler, foam underlayment (they sent me double for a job). It is 1 mm closed cell, polypropylene foam. Compressive Strength @ 25% is ≥ 40 psi. It says it can be used with radiant heat flooring, and its flammability is Class A per ASTM E 84. Does it seem like this would be good between the cells? Figured with all of the experts in here, someone might know.
Zwy
Solar Wizard
You would have to determine the compression to achieve 13 psi. That could be tricky as it is 1 mm thick.
Zwy
Solar Wizard
No give on the body filler or epoxy. It would work well probably with a spring setup.
ArthurEld
Solar Wizard
How about these between cells? Silicone Baking Mat
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Northernchateau
Solar Enthusiast
I would venture to guess a rigid material like Bondo or epoxy would do more harm then good as I would bet the cell does not expand and contract uniformly across the entire surface. Every video I have see where someone puts a straight edge on the side of the battery clearly shows where the pos & neg terminal goes top to bottom. That would mean some spots might be at 13 psi but others will be higher or lower.
IMO using a closed cell foam or rubber of at least 3/16" ( 5mm) thick would conform to the highs and lows as well as expansion and contraction way better.
The silicone material used in baking (pans, oven mitts, etc) is good to a bit over 500° F for the melting point. A thermal runaway LiFePO4 can generate far more heat than that.
While I'm interested in something for between the cells as a thermal barrier, I see no need to put something between the cells to complement or enhance the compression frame.
I use this stuff. It compresses very little but the nice thing is it's a fire barrier to 1300C and adds 0.8mm when compressed (I use the 1mm uncompressed version).
Where did you get it from?
D
Deleted member 23531
Guest
I'm just reading this and other threads as I am about to assemble my battery pack this weekend.
One trick I learned in woodworking for temporarily holding down jigs and parts while they are cut is to use CA glue on top of blue painters tape. The CA glue is pretty hard to get off, but you can often fracture it and then peel the tape to remove the residue; otherwise you can just peel the tape while the glue is still attached to your part.
I wonder if this would be a good strategy either 1) literally using blue tape + glue, or 2) similarly using VHB tape on top of polyimide tape (ie, kapton tape). The latter option would give you the cushioning and double-sided-ness of the VHB, which is thicker and more foam-y, and the electrical insulation and removability of the polyimide tape.
Just an idea; I haven't decided what I will do yet but have about 24 hours to figure it out!
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