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Time to build my 4S battery :)

Aphers

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Joined
Nov 17, 2020
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I've got my four 272Ah cells and my JBD BMS. Have now completed the top-balance.
So it's time to do the final assembly of the pack.
I'm not short of space on the boat, the pack can go pretty much anywhere. Thinking of keeping it fairly central, not too low down and obviously not within the engine space.
I'm aware of the concerns over aluminium cased prismatic cells on boats. I have some sheets of stiff 5mm foam (it's actually sold as laminate flooring underlay) and I have made up a box from this material, with sheets between each cell, just to prevent any damage from the cells rubbing against one another. I was thinking of keeping this in place and adding the conventional end plates with threaded bar. But maybe I should have something a bit firmer between the cells?

I've also got an old safe box going spare, and I could mount the whole pack inside that. Snug but doable. This would make it easy to bolt down securely, and of course it would give some protection in the event of fire. But maybe I'm better off having the pack better ventilated? I also worry about the possibility of shorts, putting everything inside a steel box...
 
I'd compress those cells of course. Since you're looking at almost 300 Kg of total compression on those cell faces, your foam will be compressed a lot - but it can probably handle it. Between my own cells, I've been using sheets of much thinner lexan-equivalent plastic material (1/16 inch, less than 2mm). Your same foam could be used on the sides and bottom of the box, as well as the top - preventing the cell sides, BMS, bus bars, and "mains" from contacting the steel case. But all of that definitely reduces ventilation. My own batteries are built with open "sides", using only wood. My ventilation is better, but my scheme has no protection against water intrusion or fire. (mine are installed in an RV.)

I'd go ahead with your plan - your box would have no less "ventilation" than any of the pre-built plastic battery packs. They're generally built with lots of closed-cell foam 'separators' and insulators inside the case, and yours sounds virtually identical, except for the need to be sure about insulating from the outer case everywhere.
 
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