I have built some wireless sensors for outdoors and have them in waterproof enclosures. However, small amounts of moisture are getting in causing condensation as the temperature changes. After some research, it seems this is a common problem with outdoor waterproof enclosures and that's why companies make breathable membranes for them like:
I have been trying to get a small set of (goretex or similar) breathable membranes but it seems like you can only get them as a manufacturer, not a hobbyist.
So does anyone have any recommendations for how to proceed?
What size enclosure are you thinking, and at what cost? You can buy NEMA-rated outdoor enclosures that will surely solve your problem, but they may be too big, bulky, and expensive for your needs.
Tyvek house wrap is air and water vapor (but not liquid water) permeable. You could try rigging up your own vent? Assuming you don't want to buy a full roll or snatch some from a construction site you could buy some Tyvek envelopes (USPS has these as well).
Chagrin:
Tyvek house wrap is air and water vapor (but not liquid water) permeable. You could try rigging up your own vent? Assuming you don't want to buy a full roll or snatch some from a construction site you could buy some Tyvek envelopes (USPS has these as well).
The problem with a water vapour permeable vent is that, on days when the humidity is high, water vapour will permeate into the enclosure.
I don't know what it's called in the US, but you can buy here a spray called DampStart. It's used on car engine HT leads to remove moisture and seal them against any further moisture getting in. Spray the inside of your enclosure and circuit board with that and, as long as liquid water (rain) isn't getting in, you should have no problems with damp. An anual respray may be needed.
newark.com does sell a few items that they refer to as "vent drains" which appear to be what the OP is asking for. However they don't provide decent specs for the lower priced items and the higher priced items are really higher priced.
Henry_Best:
Chagrin:
Tyvek house wrap is air and water vapor (but not liquid water) permeable. You could try rigging up your own vent? Assuming you don't want to buy a full roll or snatch some from a construction site you could buy some Tyvek envelopes (USPS has these as well).
The problem with a water vapour permeable vent is that, on days when the humidity is high, water vapour will permeate into the enclosure.
Allowing moisture in/out is OK so long as it doesn't allow the moisture to build up to the point where you get condensation. That would be its purpose on a house. I'll admit I'm just making an educated guess here as to how well it would work on an outdoor electronics enclosure.
Henry_Best:
I don't know what it's called in the US, but you can buy here a spray called DampStart. It's used on car engine HT leads to remove moisture and seal them against any further moisture getting in. Spray the inside of your enclosure and circuit board with that and, as long as liquid water (rain) isn't getting in, you should have no problems with damp. An anual respray may be needed.
MSDS for "damp start": 45% acetone, 20% xylene, 20% butane, 7% toluene, 7% isobutane, and 7% 2-methoxy-1-methylethyl acetate. I wouldn't make a habit of spraying that on electronics. Or anything you're fond of, really.
I've seen outdoors enclosures just filled with expanding foam so there isn't any air at all inside and hence no opportunity for moisture to accumulate. It seems like a crude solution but a pretty safe one, as long as you don't need to access the electronics afterwards.
It sounds to me as the water you see condensing is not coming from outside, but is inside from the beginning. If you seal your container in a warm, relatively moist environment, when the container gets colder, relative humidity inside will rise, even though absolute amount of water remains the same. If the temperature drops enough, some water will condense.
If you think you can get a good seal, you can try purging the inside with some canned air, which is dry.
In the past couple of weeks, I have continued to read more few articles/forums about this topic.
Here is where I am:
for the small hobbyist like myself, vacuum sealing is not practical.
I may try desiccant but am worried it will require fairly frequent changes. As long as it is at the same frequency as the battery change, this is probably ok (my sensors can currently run for about 1 month on a set of batteries)
Another option someone suggested was to completely coat all electronics with a spray sealer. Lot of people do this to RC truck electronics for waterproofing and it works well. This may be a last resort. Once you spray the stuff on, you won't be able to re-use the electronics for any other projects.
I may try to hack up my own vent to start with. The tyvek suggestion is interesting. A friend suggested finding an old gortex jacket at a thrift store and slicing it up.
I did look at NEMA enclosures but they are way too big... my sensors are in fairly small plastic boxes
I may try desiccant but am worried it will require fairly frequent changes. As long as it is at the same frequency as the battery change, this is probably ok (my sensors can currently run for about 1 month on a set of batteries)
It shouldn't be an issue; some of the good stuff can absorb moisture like you wouldn't believe. Silca gel is best - there are various brands of cat little that are fairly cheap (5 lbs for under $20.00 USD) that sold as "crystals" or "pearls" - this stuff sucks moisture; I was at a pet store once, where they had a demo setup with a spray bottle and bucket of the stuff; I ran my hand thru it - I needed some lotion afterward. I sprayed it; completely dry. I opened the bottle, and poured a lot of the water in. Still - completely dry - instantly.
When you change it - take the "old" stuff and spread it out on a clean baking sheet, and stick it in the oven on low, with the oven door open and a fan blowing to circulate the air (or let it sit outside in the sun). The moisture in it will evaporate, and you can re-use it.
bc-ne:
Another option someone suggested was to completely coat all electronics with a spray sealer. Lot of people do this to RC truck electronics for waterproofing and it works well. This may be a last resort. Once you spray the stuff on, you won't be able to re-use the electronics for any other projects.
I'd personally avoid that, if at all possible - your call, though.
Another potentially water absorber (but you'd have to put it in a special container, with some mesh or something over the top): Brake fluid. That stuff is pretty well known as hygroscopic (which is why you need to change your brake fluid on occasion, and/or bleed your brakes - and why you should never use brake fluid that is old). Unfortunately, it is also one helluva solvent, so you don't want this on your electronics, or plastics, etc. Water will be trapped by it, though, since the water will sink in the fluid.
I may try desiccant but am worried it will require fairly frequent changes. As long as it is at the same frequency as the battery change, this is probably ok (my sensors can currently run for about 1 month on a set of batteries)
You will only need to (possibly) change desiccant when/if you open the box. The project is in a sealed, waterproof container. No moisture is entering it after it is sealed...nor is it exiting (thus, your issue). Once the desiccant deals with the moisture that was sealed in the box...it will remain dry until you open it and let more moisture in.
1ChicagoDave:
No moisture is entering it after it is sealed
It's unlikely the enclosure is hermetically sealed and more likely that air is being pumped in and out due to thermal expansion and contraction. This will transfer tiny amounts of air each time the temperature changes. Unless the places the air leaks in/out happen to be at all the cold spots, this will inevitably leave some moisture behind. Over months and thousands of cycles this can build up moisture inside an apparently sealed enclosure. But the rate of transfer will probably be very low and even just a few CC of desiccant will probably keep it dry for months.
just use the airlock for a brewing kit (the 3 piece type). Take the little plastic piece out of the middle that floats up and down (making it a 2 piece type) and put a solid lid on it. Drill holes in the bottom around the tube that comes up from the container. You have now made a weatherproof vent.
You could also do the same with some small diameter pipe and a 90/180 degree fitting, just make the fitting point down. You could even put two on there and get a nice cross breeze. Maybe hang a little hammock in there.
Another option someone suggested was to completely coat all electronics with a spray sealer. Lot of people do this to RC truck electronics for waterproofing and it works well. This may be a last resort. Once you spray the stuff on, you won't be able to re-use the electronics for any other projects.
I have occasionally had to repair boards that were coated with a lacquer that couldn't be soldered through. It was not too difficult to remove the lacquer from the solder side of the board with acetone and a brush.
PeterH:
It's unlikely the enclosure is hermetically sealed and more likely that air is being pumped in and out due to thermal expansion and contraction. This will transfer tiny amounts of air each time the temperature changes.
Couldn't that be solved with some sort of membrane that would expand and contract based on pressure variation?
CrossRoads:
You could look at watertight/waterproof boxes from www.polycase.com
I can't find that any of the IP ratings specify protection from repeated heating/cooling cycles like OP is dealing with. And even if they were protected he'd still be forced to use hermetic connectors for all of his cable ingress points.
FWIW, if you ever disassemble a hard drive you'll find what I assume is the type of rubbery "goretex" vent that OP was describing. Usually it's a round, white sticker (unremovable) but sometimes it's a small, ~1x1x3cm plastic box with a filter inside and the sticker attached that could potentially be reused.
