I do agree for efoil packs but foildrive packs (3p or less) can get pretty hot. I think it’s better overall to build a large enough battery to avoid excess heating than focus on heat management.
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Curious what specific silicone potting products we’ve been using now that we’re starting to build more under board units here. In my case trying to order stuff to Canada and would love to find something cost effective for this use. Looking at silicone since it can be removed in the event of a repair.
I also thinking about that. I want to build a sort of Foil Drive but aimed at efoiling with a larger battery. It’s going to be in a 3D printed case with aluminum sheets on top and bottom and the screws passing though the case. The only way to make this watertight is to fully fill the inside with silicone. I was thinking hardware store silicone thinned down with something to make it more liquid. I’ll have to do some test but I would be interested in what people have used.
Well there’s always Raytech Magic gel. I initially saw this mentioned a while back by @Strongarm and thought it looked promising. I like that it can be easy to get into and less of a permanent commitment.
I also saw it used here by Bzhwindtalker in one of his builds.
I used it in an esc box on top of a Flite-style mast. It pours easily, is very runny, sticky and messy, but it sets after 15min. It remains very sticky (good for keeping moisture out) and it seems like it still runs a bit after it sets. So if it sets in the bottom of a container, then put that container on its side it follows gravity and pools a little. I think it’s best when it can mostly fill the volume it is poured into.
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Rather than hardware store silicone, get mold making silicone. Its a 2 part mix that you can then pour in. You will need to run a 1mm G10 board under and on top of the battery to fully insulate it from the aluminium.
The other option is to just use potting epoxy and pot the parallel cells in one piece. That way if a row fails its replaceable.
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Thanks good idea the G10 sheet and mold silicone I’ll check that out!
Love the mold making hint. Thank you @Jezza That’s led me to so many cost effective finds. Just researching acid cure dangers, but it seems the 2 part types generally aren’t acid cure. Trying to establish whether the harder durometer might be more damage resistant at the moment.
Gonna take apart my existing pack this weekend and pot it for durability!
You can use vaccum bag ( the one in roll)
Cut at the desired length. Seal one both side and pock two holes for cables glands
The material for the bag is very though and do not need to do vaccum
Question for anyone using mold silicone: are you worried at all about the lower adhesion allowing for water ingress when it loosens? Particularly around cable paths, etc.?
That’s the only downside I see of using this alternative material for potting?
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Been thinking about this even more. Basically trying to find a more cost effective potting compound for larger volumes. Seems expensive in my area.
Mold making silicone comes in at the cheapest end for a low viscosity product. But it, by design and after some testing, does not bond to anything in an appreciable manner. Which is bad for water ingress reasons if a split were to develop.
So now I’m thinking, can we coat surfaces first with something else. For instance conformal coating, plastidip, epoxy, etc. Probably not since silicone does bond to epoxy, acrylic or rubber. Likely the only solution would be a silicone conformal coat. To which the mold making silicone would bond.
What do we think?
The other thought I had was thinning hardware store silicone with silicone oil. But I have never actually done this either.
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Good point! My first idea was to thin down hardware store silicone that’s sticks to everything and it’s cheap to buy. I haven’t tried yet I haven’t built my battery yet I have been busy with other things. I’ll do a small test when i have time.
Yes. There are silicone oils that would be interesting to try.
If you really need air pressure relief, use the PRV from Blue Robotics. Granted, it only opens up if the internal pressure goes over 1 bar, which is a lot for a square box. Mathematically, your battery would need to get up to around 300°C to experience enough thermal expansion to increase air pressure that much to get to 1 bar. I’m using Gay-Lussac’s Law for this, but under realistic thermal expansion from 20°C to 80°C would be about .2 bar or roughly 3 psi.
Bought a two part clear silicone epoxy marketed for potting from AliExpress. Brand was Hauae I think. Unfortunately an initial test seems to show it doesn’t bond any better than a much cheaper mold making silicone. So not any more helpful and preventing water ingress through a seam or split. It also arrived with one bottle already cured and useless so something is amiss. Just in case anyone is venturing down a similar path.
I did buy and continue using that Ali brand. The transparent version comes in good condition. What I like about it is it’s relatively low viscosity.
I also have the brand - power gel, but it is less viscose.
In my case the connectors are epoxied into 3d printed enclosure, the silicone is poured in between the enclosure and the cells. I don’t see reason to worry here about adherence