Ingress Protection for Robotics Cases

[Wirth's Law]

Hello all,

I am planning out a robotics project that I would eventually like to use outdoors; and I am looking for any practical advice on how to prevent moisture buildup inside electronics cases.

Normally, this sounds like a job for an ingress-protected box; but the real problem is humidity in ambient air. Under normal conditions, a simple sealed box would be sufficient. However it seems if the electronics inside the box are cycled on and off throughout the day, there is a change in internal air pressure that can draw moist air past any flaws in the seal, and into the box. If this cycle continues several times, condensation will form inside to ruin the components; and if you've ever seen auto headlamps with water trapped inside, this pretty much what I'm trying to avoid.

I've seen a few vendors selling vent plugs that allow air though while blocking moisture and particles. So basically, my questions are: has anyone here tried the vent plug technique? Are these generally worth trying out? Are there any techniques you recommend?

 

[ronsimpson]

>Mount the boards so water will run off. Not flat.
>There is a spray coating to put on the PCBs.
>If you have heat problems, put fans in the box. If you are moving the same old air around it helps. If the box is aluminum, heat will transfer from the electronics to the case just by moving the inside air around.

 

[dknguyen]

Would a dessicant help? Well, not really a dessicant so much as just some powder with a lot of surface area for moisture to cling to rather than the components.

 

[MikeMl]

Over the years, I have mounted things like RF preamps, coax relay switches, matching networks at the top of my 55ft radio antenna tower. I find that leaving the bottom of the enclosure with small open weep holes works out the best so that the box is ventilated, but the holes are small enough so that insects are kept out. All of the wiring exits from the bottom of the enclosure. Each wire/cable has a drip loop. The enclosure has a skirt (lip) so that rainwater cannot run into the enclosure. Obviously, the top of the enclosure is sealed with a cap.

The enclosures are cut from**broken link removed**
The **broken link removed**

 

[Wirth's Law]

The capped enclosure approach with weep holes sounds like a good starting point. (That looks really handy for disguised antennas, too). I think I'll play around with some ideas.

A while back, I was looking at some desiccants for a different project. I haven't tried them yet, but I managed to find a good white paper on how much to use for any given enclosure size. If I can mange to find it again, I'll share the link.