# Battery box heating and insulation, fire hazard?



## Siwastaja (Aug 1, 2012)

Those self-regulating PTC heating cables are considered safe and IMO the right tool for the job, just like the polyurethane. I don't see any flaws in your idea. It's typically done exactly how you describe it. Just the normal precautions with the batteries; don't overcharge, don't run empty, make sure the interconnections are good, check for loosening and retighten as necessary. Use a BMS with a good track record and make sure it works, or if you go without one make sure that your alternate procedure is sufficient.

I think there are different polyurethane grades and some products are approved for fire protection and some are not. But I wouldn't be too worried.


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## mora (Nov 11, 2009)

Polyurethane might release poisonous gas if heated too much. I mean after after expansion and hardening. Don't put heating elements or wires in touch with insulation material. You could sandwich heating wires between thin sheets of aluminium so heat generated by wires spreads more and doesn't create any hotspots. I'd put a simple thermal snap switch in series with supply line in case wires get too hot. Same approach is used on some old seat heaters.


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## tido (Sep 20, 2011)

Thanks for the tips!

The product I was looking at is a spray in a can. it says that it is inflamable but I was wondering if it was only flamable when sprayed or also once cured. It is this product here:
http://www.homedepot.ca/produit/polyurethane-aerosol-satine/966725

Maybe I should go for solid pannels of insulation but the batteries I will put in the trunk would have been much easier to insulate with the spray.


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## Red Neck (Feb 1, 2013)

You can also get a heating blanket at one of the supermarkets and have it connected to your 220v or 120v AC connection in the car, so it heats the batteries automatically when plugged in. I'm sure you can get it for under 20$..




tido said:


> Thanks for the tips!
> 
> The product I was looking at is a spray in a can. it says that it is inflamable but I was wondering if it was only flamable when sprayed or also once cured. It is this product here:
> http://www.homedepot.ca/produit/polyurethane-aerosol-satine/966725
> ...


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## tido (Sep 20, 2011)

I have tested the heating cable stuck in sandwhich between two pink insulation pannels. result: they melted. Of course they wouldn't be in sandwhich in my battery boxes but this test is enough to make me not want to put the heating cable on insulation board.

What I will do is keep the bottom face of my boxes directly on the plywood and insulate the other faces. Since heat goes up, it should be sufficant for our cold winters.


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## dougingraham (Jul 26, 2011)

tido said:


> Since heat goes up, it should be sufficant for our cold winters.


Heat does not go up. It radiates equally in all directions. Fluids like warm air rise because it is less dense than the colder air surrounding it. But the batteries are about 1/3 aluminum foil, 1/3 copper foil which both are highly conductive thermally. There should be little difference in temperature from one end of a cell to the other.


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## Red Neck (Feb 1, 2013)

Use a heating blanket. It only gets warm, not hot.


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