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Outdoor LED Decorative Project Question
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Outdoor LED Decorative Project Question

by hopworks on Fri Nov 08, 2019 6:05 pm

Greets Everyone!

My first post here (I think, pretty sure, do not post much) and I want to say in advanced that although I think the prices are high here, you certainly get what you pay for, and the support is awesome! Adafruit is usually where I go when I start prototyping because I know my idea will work.

Anyway, I am building an outdoor decorative holiday device, (yeah, who isn't this time of year). Anyway, it requires a bit of amperage so I am using an open-frame A/C to 5vdc 10amp power supply (meanwell eps-65s-5) and everything is wonderful on my bench. But I started thinking about it being outside, and if I should install a fan in my device to cool things down. I haven't done any temp sensor logging yet to see if it is even necessary, just thinking ahead. Anyway, I started thinking about moisture. Fog, rain, that sort of thing. The whole device is encased in a moderately large acrylic tube 2 inches in diameter and (for now) open on both ends. Should I seal it up to avoid moisture from shorting it out? Should I go ahead with a fan to intake outside air to cool, and hope the heat inside burns off any high-humidity issues?

The heart of the controller is an ESP-32 and a bunch of WS2812 LED's that are mounted in aluminum guides on the outside of the tube. 160 to be exact and although my math says max 9.6 amps at full all out LED's (3x60ma per led x 160), I do not expect my light show to max out more than 5 amps. I even wrote a function to make sure I do not exceed that. I plan to install two temperature sensors also... one inside and one outside in the next layer (inside a light fixture) so I can monitor heat, and maybe even shut it down or adjust the brightness to compensate.

Am I over thinking this or what should I do to cool yet keep moisture out?

This strategy will affect many of my other outdoor ideas where a PSU is in with the project. I would appreciate any advice I can get! And I certainly appreciate your time!


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Re: Outdoor LED Decorative Project Question

by adafruit_support_mike on Sat Nov 09, 2019 3:17 am

Always collect measurements before spending too much time solving hypothetical problems. An hour of data collection is worth more than a month of design.

If at all possible, try to keep the electronics inside a fully sealed container. If you need to dump heat, use a metal shell and do your ventilation on the outside of that.

The big problem for outdoor electronics is electrochemistry: a film or moisture adsorbed to the surface of a PCB is weakly conductive. The processes that oxidize and corrode uncharged metal happen faster if you apply voltage to them, and can carry metal atoms from one part of a board to another through a thin film of water. Resistors start to grow gunk on the end whose voltage is more positive, usually along a path that leads to a lower voltage.

The adsorbed layer can also pick up contaminants like sulfides and chlorides from the air, which turn it into a low-quality electroplating bath. A board can etch its own traces down to nothing if you give it enough time, and the eventual electrical failure will be caused by conductive paths that have grown or shrunk chemically.

The best way to avoid all that is to keep boards in a low-humidity environment.

A hermetically sealed box won't allow any more water in, but will be stuck with the amount of water vapor that was in the air when it was sealed.

A box with a small amount of leakage that's warmer than the air around it will lose water to the outside. Warm air can hold more water vapor than cold air, and the theory of partial vapor pressures says that the water vapor inside a hot box is at a higher pressure than the water vapor outside the box. If the box can leak slightly, water vapor will escape until it's at the same pressure as the water vapor outside the box. That lowers the total pressure inside the box though, so the water vapor that flows out will be replaced by other gases like oxygen and nitrogen coming in. The higher the temperature difference between the inside and outside, the drier the air inside the box will be.

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