Polyurethane foam to fill DIY battery case voids?

[Luk88]

What do you think about putting some polyurethane building foam around your battery pack if you're using a toolbox for a case and you want to immobilise the pack?
(pictured)



I also have compression with threaded rods (spring loaded) and I've used this yellow foil (two layers) so I can pull cells out if needed.

This case can be used vertically this is why there is foam all the way in the bottom.

Sides are filled up by about 2in to prevent sideways motion. There is no foam up top to allow adjustment of the pressure.

What do you think? The battery will be stored underground (in a cellar) with a constant outside temperature of around 2~5C.

 

[Luk88]

Here is the layout that will be used. Cables will be tidied up and the BMS will be held to the top of the board by vhm tape. I'm not planning outside terminals, just two case holes with grommets for the cables. Positive will attach directly to the fuse. Negative will be connected to the BMS held in place by a screw going to the currently empty hole above it. The foil will be trimmed eventually. If I ever find the battery is getting too hot I'll add a fan to provide airflow over the top.


It sure doesn't look very pretty at this stage, but I think with fire retarding foam it's a rather practical method. This is 8s 280AH battery BTW. I wish they made chest big enough for my 16s 280ah battery. The chest has wheels and is stackable.

The fuse as well as the BMS platforms are held on threaded rods held in pieces of wood at the bottom of the foam. So it can be removed easily later.

For anyone wondering why do I have 3 colors of foam the answer is I bought it so long ago it hardened in its cans. I discovered it only after I finished the first can so I had to use whatever foam I had on hand.

Incidentally this brings me to a tip for anyone that wants to use such foam in their battery. Do not use hardware store foam that comes with a little screw on straw. Buy a metal pistol style applicator and so called low pressure canisters. The normal hardware store foam expands a lot and has very little strength. (it is the blue foam on the picture) After it hardened I simply crushed it and removed 90% of it with my bare hands. In contrast, the "low pressure" foam expands only slightly, but sets very hard. This is what I used initially as a test and the small amount of foam on the first photo helds this very heavy battery just fine with the chest stood up on its end. Good luck removing it with anything but a chisel.

This is the kind of applicator I'm talking about.

 

[Luk88]

The (semi) final version. Semi, because I still have to get the cable grommets. One thing I'd do differently if I was starting again is to insert a piece of plywood under the cells. I don't trust the thin plastic bottom of the chest. When I was hoisting it down to my cellar I had to be extra care not to bump the chest floor. If I ever take the cells out I'll do it.

If anyone has ideas for improvement, let me know please. The plan is to have it vertically. I wish I could find a double height chest for my 16S. It feels super solid and (hopefully) cell removal is still possible.

 

[PotusGobbleBottom]

Nice!

 

[PotusGobbleBottom]

Ever tried burning that foam?

 

[hwy17]

I see no problem with it, but I'm not sure if the walls of a plastic box are really strong enough for it to be firmly immobilizing. It will prevent shifting though.

Servicing would be the other problem, I like to avoid foams because of what a permanent mess they make. But generally we don't expect packs to need a lot of servicing either.

 

[hwy17]

Do you have separators between the cells? I normally try not to press concern on others, but in light of build issues that have come up in the community, I think peer pressuring for separation is warranted nowadays.

 

[Luk88]

Ever tried burning that foam?

The word on the can "Ogniochronna" means "Fire retarding" in Polish,but no, I haven't. Actually I might as I have some cutoffs etc. If people are interested I can make a video.

I see no problem with it, but I'm not sure if the walls of a plastic box are really strong enough for it to be firmly immobilizing. It will prevent shifting though.

I thought so too, that this thin plastic will flex and detach from the foam. It is a sort of experiment, but no. So far despite moving it quite a bit, hoisting down into a basement etc it hasn't shifted. I tried pulling it with my hands while vertical with doors open, but it feels solid like stone... So hopefully, it'll be fine. But this is low pressure foam. The blue "normal" foam. Not only didn't stick. It was so weak I could break it off and throw out.

Servicing would be the other problem, I like to avoid foams because of what a permanent mess they make. But generally we don't expect packs to need a lot of servicing either.

I've put two layers of thick foil between the cells and foam. Also the top of the compression fixture (where the disc springs and nuts are) is free of foam. The board that holds the BMS is on 4 threaded rods so it can be detached too.

So I'm hoping if I ever need to remove a cell I'll just loosen the compression screws and cells should come out. One layer of foil could bind, but two should slip (hopefully).

Do you have separators between the cells? I normally try not to press concern on others, but in light of build issues that have come up in the community, I think peer pressuring for separation is warranted nowadays.

I do, always. I use the yellow 0.25mm pcb-like material sheets. Also I put two on the ends just in case(more for mechanical reinforcement than anything else).

 

[curiouscarbon]

when maintenance is a priority, foam is usually discouraged due to difficulty of removing

two sheets of low friction material as a sliding interface to enable maintenance is an interesting concept.

expansion amount and holding force of foam suggests low pressure type is preferred for this application

deformation of the side of cell casing then becomes a concern from the foam expansion force.

it looks like there is a sheet to spread out the foam pressure, so cell dent risk mitigated.

overall this seems like a very clever way to both thermally insulate and physically secure the battery

cool!