Another Cell Compression Thread, this time about foam
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Daddy Tanuki
Solar Wizard
Dude, you just answered the question I needed answering. I am taking a 14K liter stainless tank (from a milk truck) and burying it with hot water heater elements on both ends.... (diversion tank for hot water and house heating). I was looking for an expanding foam for insulation in bulk as spray foam is not available where I am at. this stuff will be perfect to surround the tank with for insulation purposes. I can dig down, lay a concrete pad, and set the tank on it and then cap the ends with concrete for access but cover the bottom, sides and top with foam for insulation purposes thanks for the link.
2-Part Polyurethane Expanding Marine Flotation Foam
2-part expanding polyurethane marine flotation foam for permanent flotation, insulation, and soundproofing. Cures to a 94% closed cell marine grade foam.www.totalboat.com
How about encapsulate the cells in a battery box at a low SOC with 6lb stuff.
Have you had any reason to disassemble your pack and check your foam? I'm curious whether the foam you used has taken much of a set. I came across this thread while researching PF100. I would much prefer to use appropriate foam and not have external springs.
Honestly, I wouldn't expect much set in closed-cell neoprene at 25% compression, but it would be nice to see real data. If you have some left over, perhaps you could run a test for us.
Zwy
Emperor Of Solar
I went to Poron now, I do have the one pack with the USA Sealing Foam in it but it would be a royal pain to take it back out and apart.
I'll look and see if I have some left over, I might be able to run some type of comparison to Poron once I get my house 48V system installed later this year. It would probably be a year before any results from that test.
Thanks. I did notice that even PF100 specifies the set only after a short period, and with some elevated temperature. The stuff still seems a bit hard to find, and it isn't nearly as cheap as other foams.
No time like the present to get started on a long-term test for the sake of science! LOL. Maybe put a measured area of it under some measured weight (books, perhaps) and measure the compression (by measuring the gap), then measure the gap every month. You could also then unstack it right after that monthly measurement and measure the pad thickness, then restack it. We would love to see the results.
Zwy
Emperor Of Solar
Zwy
Emperor Of Solar
You have to ask for a quote from various outlets, you can try Rogers for samples or companies like this. https://www.srpco.com/gaskets/poron-evextend/
You could ask McMaster Carr also as they do carry some Poron and might be able to order the EVextend. https://www.mcmaster.com/poron-urethane-foam/
Maybe as insulation between cells. It’s my understanding that what you’re looking for is Neoprene that when place between the 30%SOC cells and compressed its COMPRESSED thickness @25% will provide approximately seven psi. Further when the batteries expand each approx .5mm, the resulting compression does not exceed 17 psi. Seems tricky but I’m getting samples through AliBaba and the price should be around $4-5 per pad. Need to test them with FORCE GAUGE!
Batteries cells naturally compress and expand into environment and state of charge. According to the manufacturers life is extended if they are compressed at approximately seven psi and never exceed approximately 17 psi.
Please read my other replies in this post for a better understanding of the type of material that I have decided to use through extensive researchI bought my batteries before I found this forum based solely on the capacity I needed to run my fridge and the fact they were in the US. If I had found the forum first I would probably still be trying to decide what to get.I'd probably also still be waiting on cells to ship from china.
My cells came with a couple of long zip ties and a small roll of double sided squishy tape to stick between them. I thought the foam was an odd choice until I saw the cells beginning to swell and the pack got over 1/4" wider the first time I charged them up. I want to add capacity down the road so may have to reconfigure and I didn't want to damage the cells trying to pull them apart, so I instead slipped some 1mm thick foam sheets between my cells. I cut the foam from some packing envelopes that got away from someone and floated into my yard after a thunderstorm. I cut them a little bit long and used slits in the tops to keep the bms wires organized. After seeing a couple of drop-in LiFePo4 battery teardown and reading a couple of posts here on the forum I modified my cell holder to fit snug around the cells and constrain them, and I haven't noticed the pack moving any more. These are 200ah cells. I imagine the larger cells expand more.
Also, before I found the foam envelopes in the yard, I was going to experiment with paperboard or cardboard or construction paper between the cells to allow them to move a little bit. I was also considering something like felt or fiberglass matt, anything to let them flex a little bit but remain constrained.
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Tape will hold them together quite well however they do not allow for proper compression if your goal is to achieve longevity
Looking at ways of compression for the battery pack that i am building. Anybody using EVA foam ? It is easy to get hold off and cheap. The stiffer types like EVA75 seem to be a relatively good fit, even if the compression set is a bit high from some manufacturers.
I guess the main problem is the lack of reliable datasheet on the EVA foam from hobby stores.
It seems to be impossible to get Poron or similar foams in Europe, especially in Scandinavia.
I guess the main problem is the lack of reliable datasheet on the EVA foam from hobby stores.
It seems to be impossible to get Poron or similar foams in Europe, especially in Scandinavia.
You might want to get a small piece and test it for memory (taking a set when under pressure). I tested a sheet of closed cell ethafoam by resting a lead-acid battery on it for a few weeks. It took a set pretty well, but it eventually came back to the original shape. The point is that you want a foam that continues to apply the same force under compression, even after long-term use.
It seems to me that Poron may be a special blend of neoprene foam, similar to wetsuit material (but without the cloth layer). If I can get the time to set up my strain gauge, I plan to do a long-term test of various foam materials.
curiouscarbon
Science Penguin
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cool!
the EV specific poron, couldn't source
got some light blue poron rolls on amazon
"poron 4000 royal blue"
it's the type for padding prosthetics and stuff though, i think. still should be fun to rest a cell on it for a while and observe any deformations
Zwy
Emperor Of Solar
Poron is open cell. This allows elasticity over time where as closed cell will lose the air in between cells over time.
I've read hundreds of posts about compression and all the clever ways of interpreting/achieving the force that the cell manufacture's data sheet calls out, so I'm wondering why two of the largest battery manufacturers, CATL and EVE just take a very simple approach: They just line up the cells, apply X-amount of force and then quickly laser weld an aluminum sheet metal surround and call it good? No springs, no foam, no insulation between cells. One would think that if they're mass producing battery packs made of prismatic cells they would be very concerned about getting it right or face a ton of product returns or potential damage liability.
You can see in the following two videos that they do compress the cells before welding up the case, but there's no evidence of any method or mechanism that would allow the cell to "breathe" once it's fixture was set.
These are the guys that are writing the data sheets that we're trying to interpret, wouldn't this be a physical example of what they're trying to say?
EVE Pack Assembly. Note the compression mechanism at the 30-second mark of the timeline.
CATL LFP Battery Production. Cell compression starts at about the 1:58 point in the timeline.
You can see in the following two videos that they do compress the cells before welding up the case, but there's no evidence of any method or mechanism that would allow the cell to "breathe" once it's fixture was set.
These are the guys that are writing the data sheets that we're trying to interpret, wouldn't this be a physical example of what they're trying to say?
EVE Pack Assembly. Note the compression mechanism at the 30-second mark of the timeline.
CATL LFP Battery Production. Cell compression starts at about the 1:58 point in the timeline.
curiouscarbon
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The extra length of springs is unappealing to me.
By using threaded rod and load cells, I intend to monitor the pressure and loosen if it goes too high.
Ideally, I wish for no/minimal deformation of the case while also staying below the max pressure figure in datasheet.
Thank you for the post and videos!
Interesting that they pre-apply the force and then laser weld in place. quite clever in my opinion for quick/efficient manufacture ability.
By using threaded rod and load cells, I intend to monitor the pressure and loosen if it goes too high.
Ideally, I wish for no/minimal deformation of the case while also staying below the max pressure figure in datasheet.
Thank you for the post and videos!
Interesting that they pre-apply the force and then laser weld in place. quite clever in my opinion for quick/efficient manufacture ability.
curiouscarbon
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good point. if the fixture is solid, the need for extra insulation to mitigate vibration induced chafing should be reduced.
would be cool to include some sort of force sensitive resistor on each end of the pack to detect serious overpressure failure mode.
cheap material wise.
careful observation of reports indicates that expansion/contraction of the cell is confined mostly to the center of the face, so the sensor does not need to be the full size of the cell, in my opinion
e.g.
TorC
Solar Enthusiast
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Interesting find, @Dan1376. On reading that I start to wonder what the reason for the cell compression cycle life graph really is. I'm currently wondering if it could it be that the force per area measurement means nothing, and it's really a question of limiting expansion, with the force having as much to do with the case corners and how they deform to provide optimum pressure internally.
Even the test setup design that produced that graph: have we been misinterpreting them all along, and the design really is, "At X SOC assemble a fixed case with P pressure at time of assembly."
Even the test setup design that produced that graph: have we been misinterpreting them all along, and the design really is, "At X SOC assemble a fixed case with P pressure at time of assembly."
One important thing to remember is that when they design a mechanical enclosure they can design it with enough compliance to account for cell expansion and contraction.
Thin steel/aluminum plates are springy. There is no problem to make a metal case without springs if the case itself will act as the spring. I am 100 % sure that these thin plates that is being welded shut will deflect 1-3 mm under 300 kgf. For smaller packs that is sufficient.
For us that does this diy, it is a bit more difficult since most of us does not run simulations on optimal case thickness to ensure that the case is sufficiently compliant.
Thin steel/aluminum plates are springy. There is no problem to make a metal case without springs if the case itself will act as the spring. I am 100 % sure that these thin plates that is being welded shut will deflect 1-3 mm under 300 kgf. For smaller packs that is sufficient.
For us that does this diy, it is a bit more difficult since most of us does not run simulations on optimal case thickness to ensure that the case is sufficiently compliant.
matt2006
DIY Solar since 2016
I was told by a guy that builds Ford Rangers into EV's that EVA foam is the best for between lifepo4 cells.
Zwy
Emperor Of Solar
EVA foam is closed cell. Over time, it will compress without returning to original thickness as the air/gas in the voids eventually will leak out under long term compression. Second concern is flammability, I didn't look to see what standards it meets but one should research it before using EVA foam.
curiouscarbon
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poron foam uses the mechanics of the material to push back, from what i gather, (less degrade over time?)
some foam use force of air bubble to provide push, but it leaks out of small internal holes/pores. (more degrade over time with air leak.)
(degrade = force reduces over time with continued pressure)
i'm still learning
thank you everyone for info!
some foam use force of air bubble to provide push, but it leaks out of small internal holes/pores. (more degrade over time with air leak.)
(degrade = force reduces over time with continued pressure)
i'm still learning
thank you everyone for info!
