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Water resistant fan vent? — Parallax Forums

Water resistant fan vent?

Roger PiersonRoger Pierson Posts: 62
edited 2008-02-07 18:20 in General Discussion
I have a project I will be enclosing in a weather proof case, but I need some way of ventilating the electronics without letting water in. Surely this is a problem somebody in the world has made a product to solve. I don't seem to be able to find anything on the net though. Any suggestions?

Roger Pierson
Senior Electronics Technicain
DTI Assoicates


  • parskoparsko Posts: 501
    edited 2008-02-05 16:09
    I think your only reasonable solution is a heat sink mounted to your case to draw the heat out. If you let air out (from inside) to vent your electronics, you'll need to replace that air with cooler air(from outside), which in turn will allow water in. Or is there a detail you left out? Are you talking about water, or water vapor?

  • Bruce BatesBruce Bates Posts: 3,045
    edited 2008-02-05 16:25
    Roger -

    Once successful method is to use a semi-permeable, fabric membrane like those made by W. L. Gore (link below). Dr. Tracy Allen swears by this method for his environmental monitors and other outdoor devices. Here is the link to their venting section:

    Another method which is not quite as high-tech is to use mesh venting buttons which can be inserted in holes cut in the enclosure. They generally range from about 2" - 4" in diameter, and snap into the hole. In the center is (usually) a double layer of stainless steel mesh. I'm hard pressed to find a picture of one at the moment - sorry.

    Yet another acceptable means is to use vent louvers such as these:

    The key to choosing the best method, is knowing or calculating what kind of CFM you want to move through the vents, no matter which one you choose. The more restrictive the opening is, the higher the static pressure will be inside the enclosure. The larger the opening(s) are, the more CFM you can move.

    I hope that gives you some viable options.


    Bruce Bates

    There is no pleasure in having nothing to do;
    the fun is in having lots to do, and not doing it!
  • steve_bsteve_b Posts: 1,563
    edited 2008-02-05 16:34
    How hermetic do you want this thing sealed?

    We have some gear that we keep sealed from bugs and other nasty critters (moisture as well).
    Basically, it's a big box that has a copper plate/panel in one side of the enclosure with heat sinks mounted to them with thermal compound. Then there are fans on the inside that pass around that hot air and fans on the outside that get the heat away from the heat sink. It does a fair job actually!
    I would've liked to see a piezo element used with a big heatsink and fan on the hot side.


    What's the best thing to do in a lightning storm? "take a one iron out the bag and hold it straight up above your head, even God cant hit a one iron!"
    Lee Travino after the second time being hit by lightning!
  • Roger PiersonRoger Pierson Posts: 62
    edited 2008-02-05 21:42
    Thanks for the responses guys. Keep them coming! I'm researching the products Bruce mentioned.

    To answer your question, Steve, I'm willing to tolerate a bit of moisture, but I need this case to protect the equipment from rainfall.

    Roger Pierson
    Senior Electronics Technicain
    DTI Assoicates
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2008-02-05 23:45
    The setup that steve_b refers to is called a "heat exchanger". This might help with any Googling you're doing...

  • Tracy AllenTracy Allen Posts: 6,658
    edited 2008-02-06 07:11
    I do like the Gore proVents, but they are not meant for heat transfer, nor would they be suitable for anything involving a fan. It depends on what you mean by "ventilating".

    They do allow equalization of pressure from inside to outside of an enclosure, as for example in venting gas that might build up from (bad) charging of a battery, or pressure that would otherwise build up from extreme temperature changes. They do keep the liquid water out.

    But it is still possible to have problems with condensation. Gore claims that condensation problems are also reduced by the vents, compared with an enclosure that has uncontrolled pressure exchanges through imperfect seals. It has to do with keeping the even pressure and allowing vapor exchange. I am inclined to believe it from experience, but I can't say that I understand what is going on with the thermodynamics.

    Gore offers materials with many levels of ability to resist water pressure and correspondingly many levels of water vapor resistance. They also have membranes for specialized applications, for example, to protect microphones.

    Tracy Allen
  • steve_bsteve_b Posts: 1,563
    edited 2008-02-06 14:11
    I remember a story, from work, of an engineer that went out in the field to install some prototype equipment.
    It was a week of hot days and cool nights. By the end of the week he couldn't open the door on his equipment enclosure (had to drill a breathing hole).
    So then the problem was that bugs and moisture could get in.

    He then proceeded to take a condom out of his wallet and glue it to the hole in the box. That took care of the pressure changes (apparently the condom would blow up in the day and go limp at night --- uh. nono.gif

    He came back to find the condom filled with some moisture....he changed it out for stronger balloon and some dessicant. It was clever and macgiver-ish and worked!

    I think goretex allows for breathing, but not air transfer. What's your equipment rated for? Up here in Canada, we have to balance between good cooling in summer and self-warming in winter (+30degC summers and -30degC winters make it a challenge!).


    What's the best thing to do in a lightning storm? "take a one iron out the bag and hold it straight up above your head, even God cant hit a one iron!"
    Lee Travino after the second time being hit by lightning!
  • David H.David H. Posts: 78
    edited 2008-02-07 18:20
    You could use 2 enclosures. The outer enclosure could have vents on the bottom, and the internal enclosure would have vents on the top. This would keep the rain from getting inside the internal enclosure.


    There are 10 types of people in this world,...
    Those that understand binary numbers, and those that don't!!!
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