Another Cell Compression Thread, this time about foam

[Zwy]

I looked up EVA foam but I never used any. Not sure what it is.

I guess if the closed cells burst, then it becomes open cell?

Flammability is a big thing, the neoprene I used back in the early days would only burn if you held a torch flame to it. Basically melt more than anything. I can't recall if the test photos are in this thread or another. The reason many foams used in automotive applications are fire resistant like the neoprene I tested was due to federal safety standards. There is an ASTM standard for it.

 

[Skypower]

I looked up EVA foam but I never used any. Not sure what it is.

I guess if the closed cells burst, then it becomes open cell?

Flammability is a big thing, the neoprene I used back in the early days would only burn if you held a torch flame to it. Basically melt more than anything. I can't recall if the test photos are in this thread or another. The reason many foams used in automotive applications are fire resistant like the neoprene I tested was due to federal safety standards. There is an ASTM standard for it.

Well I kinda got snookered. I typed in Poron on Amazon and this foam popped up. Thought it was the same thing under a different name. It was cheap and I was tired so I bought it. It showed up and I started cutting. If seemed good but had left something heavy on it and it left a pattern. I looked closer at the rapping and????. Started a search; Poron vs Eva foam and got educated. My fault for not looking closer for the bait and switch. I’m sure I’ll find uses for it like sound deadening or packing material. As for burning, it’s far from self extinguishing.

 

[Skypower]

Running some tests on this EBay “Poron foam” It measures .128 to .130”. At 12 psi its thickness is measured at .085-.090” (6 square inch test sample). Checking rebound to size tomorrow. A cursory look seems like this will work. The plans are for a 1/4” G10 plate at each end of the stack, one foam sheet on each end of the stack(4S) and insulators between each cell. For a stack of 8 cells I’d probably go with two 1/8” foam sheets on each end. Foam on the ends of the stack will not put as much movement on the flexible buss bars and also help keep the end cells more temperature stable with the others. With four cells and 2 sheets I’m anticipating squeezing the stack total of .08” from contact hight. I will either use metal strapping or two long hose clamps with fiberglass insulating sleeves to hold it together.
This is a much different design from before which used a centralized spring but this time I don’t have the room and this is much simpler.

PORON 4701-40 Foam W/Adhesive Backing - 12.375" x 9.375" x 0.125" - Box of 10 | eBay

PORON Black 4701-40 Polyurethane Foam With 1173B Acrylic Pressure Sensitive Adhesive. Compression Set, % max @ 23°C (73°F): 5. Quantity: 10 sheets per box. Maintains integrity in lengthy temperature fluctuations.

www.ebay.com

 

[tinyt]

My suggestion is do not remove the adhesive backing cover, I don't want anything sticking on the sides of the cells. If I have to replace a cell, it will be easier to re-assemble.

 

[Skypower]

My suggestion is do not remove the adhesive backing cover, I don't want anything sticking on the sides of the cells. If I have to replace a cell, it will be easier to re-assemble.

Wise advice, but I wasn’t even going to consider sticking it to the cells. I might just install it to the end plates. By the way, one sheet will do one surface and one more that you have to peace together(stick to an end plate). Only two pieces of scrap. Just did a little fire test on the thin piece. It burns like a candle wick . Guess I’ll just use another Formica insulator sheet and sandwich it to the G10 to help reduce the fire danger a bit.

 

[Skypower]

Well, the rebound to original size test was excellent. 98% within 1 minute and 100% within 10 minutes(my own test values vs Eva). As far as flame retardant goes I have no clue as to what the spec numbers mean and not going to educate myself to that useless value. I just know it’ll burn so let’s just limit the surface area and call it good. Is this Poron? Mechanically it acts like it so it’s a go for project.

 

[Zwy]

My suggestion is do not remove the adhesive backing cover, I don't want anything sticking on the sides of the cells. If I have to replace a cell, it will be easier to re-assemble.

I glue mine on. I can always get more Poron. I have successfully removed the sheet but not on a cell that has been in service for a few years. Heat gun might help.

 

[Skypower]

Well some bad and great. The two hole terminal cells don’t fit in the black box where the old threaded terminal cells did. The two holes terminals are too high and interfere with the inside lid terminals. So I looked around and found a stainless box on Amazon that’s a bit bigger in all directions. It was actually cheaper than the plastic box. Bought some “bulkhead terminals” too. It’ll be really interesting to see how close I have to get for a Bluetooth connection(JK). Used cut to size hose clamps with fiberglass protective sleeves. Uses very little space for the sides and way strong enough as long as the gear box tang is supported by a surface. Easily tightens to the foam preload I calculated. Rounded corners are important to make the band tension equalize on each side.
I put down some Poron foam in the box bottom 1/4 total. Next I’ll fabricate a bracket to hold the cells down and mount the bms, fast blow fuse and breaker.