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Thread: High humidity environment

  1. #1
    Member dimitre's Avatar
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    High humidity environment

    Hello, I'm developing an installation meant to be in a high humidity environment (91%) and I want some advices of how to protect the electronic equipment on it.
    It is meant to run during one year.

    Teensies will be attached on a PCB with ethernet controller, I'm wondering if electronics varnish over the PCB and the teensy will be enough to protect, or if I need some better protection.
    I've tested wrapping the entire board using thermo retractable (photo attached)

    Other pieces of the system
    Raspberry PI - thought of coating with varnish or dig into mineral oil
    ethernet switch - thinking of using kitchen film to wrap it with the cables plugged
    usb webcam Logitech C270 - using without protection at all.
    AC connections - without protection.

    Other ideas? maybe using food vacuum selaer machine?
    Thank you!


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  2. #2
    Senior Member+ Theremingenieur's Avatar
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    Hammond Mfg does produce several series of housings for electronic projects with different IP (humidity protection) classes. I'd go for that instead, to prevent thermal or condensation problems: https://www.hammfg.com/electronics/small-case

  3. #3
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    Anything that leaves air inside WILL pull moisture in during temperature cycling. Basic principles are:
    Conformal coatings of various sorts work well, but are tricky with buttons and plugs
    Electronics can survive remarkable amounts of moisture as long as voltages are not to high, and exposure is not too long
    If moisture is allowed to persist metal parts will vanish due electrolysis and make for really weird faults.
    Any component that needs exposed metal to work needs a plan (switches/plugs/testpoints), for copper,tin and silver legitimate plan can be 'Clean it when I need that contact to work again' and just let corrosion build up (iron changes volume, which is a problem).
    Things like plugs can often survive well if left alone (and plugged in) as contacts protect each other. Every time you move a plug where contacts are exposed to hostile environments you are playing roulette though.
    Keeping temperature stable prevents condensation, and also temperature related pumping of moist air in, so adding heaters or careful use of waste heat and insulation helps.
    Making sure water can get out is more important than stopping water getting in
    There are solutions for the volume changes from temperature cycling involving flexible membranes or oil filled tubes but they are fiddly to get right
    You can get bulk desiccant packs, fit a humidity sensor and replace as required.
    Or for the really complete solution use dry air generation hardware and positively pressure (overkill for this project)
    Last edited by GremlinWrangler; 02-13-2019 at 07:32 AM. Reason: edit

  4. #4
    Member dimitre's Avatar
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    Thanks. In this case I'll prefer to coat everything.the thermo rectratable option have this problem of holding humidity inside.
    I'll try to spray with everything plugged so there are no holes filled, and I think I dont have problems with buttons (maybe Teensy reset button)

  5. #5
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    Simple (electrical) varnish coating will be ok for higher %RH environment where absolutely nothing comes out of solution; that is, non-condensing. Otherwise the only two solutions (pun unintentional) that have worked for mine and my employers' stuff is either an IPx4 or better rated enclosure, or full encapsulation. The other possible solution (mostly for our factory ATE stacks) is to keep the immediate ambient heated when power not applied, such that nothing is ever allowed to condense.

    Mil-Std 810 part 3 has global environmental guidelines and Mil Std 883 has test methods for equipment intended for high humidity environments.

    Finally, carefully and with mindfulness, research the material properties for all of the components in the assembly. There are many plastics, epoxies, and coatings that are, or can become hygroscopic. Remember, even Arrakis eventually got wet.

  6. #6
    Member dimitre's Avatar
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    Thank you @BJB.
    About full encapsulation you mean a sealed box or equipment wrapped in something?
    Maybe a good thing it doesn't have temperature variation, it will be always 10°C

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