Drascomber
regular
Reged: 17/01/2006
Posts: 311
Loc: Surrey England
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If I want to waterproof a PCB can I just stick it in a mould and fill with resin?
If so - which resin? Polyester or Epoxy?
If not - what?
Do I have to do anything special with the wires or just make sure that the end of the insulation is inside the resin?
Can I do the same with the back end of a switch? (There is a rubber oover on the fron, toggle, end)
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cliff
regular
Reged: 15/04/2004
Posts: 5843
Loc: various
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I would use Vaseline to waterproof it or multiple coats of spray on lacquer. Resins set hard and can give of a lot of heat on curing.
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 Artificial Intelligence is no match for Natural Stupidity
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Rogershaw
regular
Reged: 03/11/2001
Posts: 1391
Loc: Me: Johannesburg South Africa ...
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What you need is potting resin.
here is one supplier.
Try google "potting resin"
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Login_name
regular
Reged: 07/05/2008
Posts: 555
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As already said potting resin is "the" answer, but if you've got polyester or epoxy resin lying around then either can be used.
As Cliff said they can generate heat so either build it up in a few layers (difficult to do properly with epoxy), use a retarder or fill it with something to reduce the volume of resin. You could play around with reducing the amount of hardener or even slow it down by bunging it in the fridge.
No need to worry about the wires, just make sure that the insulation won't be affected by the resin. Depending on how it's going to be used it may be an idea to put extra insulation at the point it comes out of the resin simply to reinforce it at a potential weak spot.
I would be reluctant to "pot" a switch unless I was absolutely positve that no resin could get inside. Personally, I would resort to good old self amalgamating tape.
IIRC You can also get potting resin from Maplin.
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Billjratt
regular
Reged: 09/09/2004
Posts: 1026
Loc: Prestwick
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Used to be called "potting compound" if the shop assistant is confused.
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Yours, etc. etc.
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Login_name
regular
Reged: 07/05/2008
Posts: 555
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You're right, Damn it! I knew when I wrote it that something was wrong, but my brain didn't function properly!
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lw395
regular
Reged: 16/05/2007
Posts: 906
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Spraying on a varnish or similar may be better. It's called 'conformal coating' in the trade. The wrong resin can stress surface mount components. The preferred stuff for coating is usually acryllic iirc, but I have used ordinary poly varnish. There can be issues if its any kind of radio circuit.
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whipper_snapper
regular
Reged: 09/08/2006
Posts: 1547
Loc: Kenya
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Interesting question. I have a small, specialised VHF receiver which is not intended for use at sea and I had wondered about the best way to seal it.
I like the idea of simply encasing it in a block of resin! But I worry about a component cooking because it can't shed heat (although it is very low power - actually powered by the computer USB) and about the resin screwing up the tuning. I imagine that resin getting into coils and capacitors will change their characteristics. Any comments or suggestions ?
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Ruffles
regular
Reged: 26/02/2004
Posts: 1003
Loc: Boat: Portsmouth, Us: Stewkley
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Problem with potting is (or certainly used to be) that it acts as an insulator. So anything the emits more than a few milliwatts needs a heat sink taken outside the resin.
Also some components can't be immersed. I believe electrolytic capacitors can't.
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Rob Owen
Ruffles
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Drascomber
regular
Reged: 17/01/2006
Posts: 311
Loc: Surrey England
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Thanks guys.
Epoxy is what I have to hand so will try with that.
Holes in switch plugged with Blue Tack.
We will find out tomorrow whether solvent glued ABS sheet from the model shop works as a mould.
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markdj
regular
Reged: 31/07/2002
Posts: 673
Loc: Strangford Lough, Northern Ire...
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I would use either heatshrink, self-ammalgamating tape or just WD-40 on exposed areas as many components need the air circulation. Resin is a very permanent and unchangeable.
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Drascomber
regular
Reged: 17/01/2006
Posts: 311
Loc: Surrey England
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Update:
Used epoxy that was to hand (coloured with black tint from a polyester gel coat repair kit) - worked fine.
Solvent glued ABS sheet from the model shop worked great to make mould.
The switch part of the job failed though. I thought I had filled all the holes but obviously not as the 'poxy got inside and locked the switch up solid.
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