|Subject:||Re: [TowerTalk] Weatherproof Sealant|
|From:||Jim Lux <email@example.com>|
|Date:||Tue, 11 Jan 2005 09:48:08 -0800|
At 07:17 AM 1/11/2005, Keith Dutson wrote:
I need to weatherproof a relay box. Under test conditions it accumulated an inch of water in the bottom over a six month period. What is a specific brand of silicone sealant recommended? I understand the kind with vinegar smell (acetic acid) will corrode electronics components in a sealed environment. Also, is there a need to insert a desiccant in the box?
Weatherproof or waterproof?
Are you sure it's the silicone leaking?
How is the box vented? If the box is totally sealed, the pressure differential can get pretty high as temperature changes (to a first order, if it swings 0 to 40 C, about 1 -2 PSI). That kind of pressure can suck in a LOT of standing water, if there's a path.
An inch sounds like an awful lot to accumulate by condensation, but, you never know. If the box is set up in a way that accumulated rain water can be sucked in, and there's some form of trap ( imagine a tube from outside running up inside the box, and opening at the top. Water can suck in, up the tube, run down the outside of the tube into the bottom of the box, but then, when the pressure increases, it just blows air out the tube. Over time, it makes an effective pump.
All manner of rubber seals and/or silicone with tiny gaps and crevices can also act as a nice one-way valve. In combination with the pumping effect of temperature change, it can pump an amazing amount of water in.
If you don't need "waterproof sealed", then a vent hole at the bottom may do. Maybe what you really want is "rain-tight" (NEMA-3?)
As far as sealants go..
The "bathtub silicone" with the acetic acid will only outgas for a while. Eventually, it will be fairly inert.
There are two part RTVs and single part UV cured sealants available which are suitable for potting electronics. Check the Mouser, Digikey, or Newark catalogs. Or, if you have a local source for these things, call them up. Here in Los Angeles, I've used Sil-Pak in the past, but that's just because they were down the street from where I worked at the time.
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
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