I've been running my outdoor Arduino project for a few weeks, and I am seeing condensation on the inside of the box. I am using the following NEMA rated polycase which is supposed to be weatherproof. I also coat the microcontroller with Corrosion X; however, I do not coat the outside of the enclosure with it.
I do have a PG Cable Gland running wires from the outside of the box into the enclosure; however, I don't think I see condensation building up around that. The condensation is building up on the inside of the plastic cover, but not on the microcontroller (not from what I can tell).
The condensation does seem to build up after a good rain or sprinklers go off. How can I prevent the condensation? Am I doing something wrong?
You can get condensation in a sealed container because when the temperature drops the relative humidity increases even if the absolute humidity remains unchanged.
If I could get by with a cheaper outdoor enclosure that'd be great, too. The polycase outdoor enclosures are fairly expensive. They are being used in a garden (not submerged in water).
The more sealed You try make enclosure the more sure You will get condensation. The normal air contains humidity and enters the enlosure when air preasure changes. The variation in temperature does the rest.
Either increase the ventilation and prepare drainage for the condensation, or use water free gas, N, to overpreasure the enclosure.
I've never tried that, but I was reading in the forums that people use it with pretty good success (and it's fairly cheap). I will definitely try that out!
My other question is... if I use Corrosion X on my board, cable glands, and silica gel (or vents), is it worth buying the weatherproof NEMA polycase enclosures?
Inverted bucket: allow the moisture to go out. In other words: a few big openings at the bottom of the container. I'm using very cheap containers (something like 1-2 USD a piece) in my very humid climate with sometimes massive rain storms, and it works great, especially when you have your electronics powered on at all times, heating up the interior by a few degrees over ambient. That way 100% humidity in ambient air drops to 90-95% or so in your container and you don't have condensation. A conformal coating does the rest.
It is VERY hard to keep moisture out. When the temperature goes up, the pressure inside increases, and air is pushed out through the tiniest of leaks. Then when the temperature goes down (e.g. when it rains) the pressure drops and air is sucked back in, often with lots of moisture.
when I worked in food processing plants - used a lot of totally enclosed motors but had a small hole in the bottom (about 1/8 inch or so) to let the case breath a bit - else hit a hot motor with cold water and the motor would suck water in even though the motor was sealed
had another case - control panel would get moisture in it and set off the high humidity alarm - used silica gel packets and still had problems - in the end added a very small amount of air flow from air that had been dried out - the instruments provided the heat and the problem went away
moral of the story? very hard to keep a sealed box dry on the inside when the box meets water
I'm using very cheap containers (something like 1-2 USD a piece)
Would you mind sharing a link to your containers?
moral of the story? very hard to keep a sealed box dry on the inside when the box meets water
It sounds like it's going to kind of specific to my implementation. I can put some small holes on the bottom of my enclosure and add some silica gel and see how it goes I guess. The enclosure is small (2"x2"x2" and 4"x4"x4").
these and these are the containers I use. The latter is available in three different sizes, and for a little extra (RMB 5-6 or so) you can get the second with 12V DC adapter built in even.
czu001:
Would you mind sharing a link to your containers?
It sounds like it's going to kind of specific to my implementation. I can put some small holes on the bottom of my enclosure and add some silica gel and see how it goes I guess. The enclosure is small (2"x2"x2" and 4"x4"x4").
Don't put silica jell into open containers. It will suck water until it just leaves a puddle of goo. They are for sealed containers, only.
How much power budget do you have free in the enclosure?
If sufficient, warm up a 1-5 watt resistor, to keep the interior just above ambient.
That may help.
In an expensive commercial product, I’d be inclined to use the best solution to equalize pressure in the enclosure so the humidity would not condense. I can highly recommend the Gore product line for this purpose but it’s probably not practical for a one off.
DigiKey does have a series of similar products from Amphenol and others, I have not used any of these devices but they look quite similar.
Just had a look a couple of the Amphenol products and it looks like they’re probably using the Gore membranes in their own design plugs. It’s a special polypropylene material with holes large enough for air molecules to pass through but not water molecules. Same stuff as Gore-Tex fabric used for breathable clothing.
lastchancename:
If sufficient, warm up a 1-5 watt resistor, to keep the interior just above ambient.
Just the heat of the electronics (12V to 5V buck converter; 5V to 3.3V linear regulator; ESP8266) is for me enough to have a 3-5 degree C temperature increase as measured by an on-board temperature sensor vs. an external temperature sensor. No need for an extra heater!
FYI those vents on DigiKey are awesome! They work great so far. I’ve splashed and even submerged them in water on a hot sunny day and still no condensation!! Thanks so much!