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Moisure build up in sealed unit

  1. Jul 6, 2017 #1
    Hi guys, so im building this light fixture as a concept an inside of the light fixture is a sealed cavity which houses the power supply and control gear. Now to service this unit that cavity opens up, but lets say on a hot humid day the unit is opened and that air enters the cavity. Its then closed until next time, but in the meanwhile every night just before the light switches on it becomes very cold and the moisture in the close environment condensates on my electronic or onto the roof and causes problems, or am i over thinking this?
  2. jcsd
  3. Jul 6, 2017 #2


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    Hello Johann, :welcome:

    You are not over-thinking this: moisture and electronics can be a serious cause of problems. You have some worse-case scenario and try to think of a design that minimizes the risks: shape, materials choice, perhaps even a membrane to let the moisture go out with air when the unit is warm, ...
  4. Jul 6, 2017 #3
    As i feared haha, so do you know of any material i can rad up on or do you think its up to doing some experiments ?
  5. Jul 6, 2017 #4


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    Don't know of any reading material. (no expert, just a physicist).
    Common sense can get you a long way: spray-paint sensitive circuitry (if present).
  6. Jul 6, 2017 #5

    jim hardy

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    search "conformal coating"
    i'd leave a small vent hole at bottom so it can breathe and water will drip out.
  7. Jul 6, 2017 #6
    How about a bag of silica gel desiccant? It can be regenerated on a fixed schedule, or (if an indicating type is used) whenever the color changes.
  8. Jul 6, 2017 #7
    I think this is the best idea thank you
  9. Jul 6, 2017 #8


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    So called "sealed lighting units" are rarely air tight. Temperature changes can cause the air inside to expand and contract pushing past gaskets.
  10. Jul 6, 2017 #9


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    Use a small vent hole, say 1mm. Plug it with a fine synthetic felt or thread filter to keep insects out.

    You must decide if the vent will be at the bottom to drain liquid, or sheltered at the top, where the lower density water vapour component will be concentrated. Since condensation is the problem, a top hole is indicated.
  11. Jul 7, 2017 #10
    Vent hole is OK only for limited climate variations. If the speed of the temperature change is too fast then moisture can't get out in time.

    Coating might be OK, but that also has limits.

    If it is really a sealed space then a bag of desiccant is your friend. Replace if every time when you open it and it will be fine.
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