LowPowerLab Forum
Hardware support => Projects => Topic started by: xavier on October 11, 2016, 12:08:49 PM
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Would anyone have some suggestions for preparing boards for the outdoors? I have the following setup for my weather station and it works great in summer but a little of humidity seems to be killing the battery charger (I think).
I think the breadboard is probably not the right way to go (as I did) but if I were to just use wires and heat shrink them to the moteino would that be good enough?
I have another moteino around that I could solder below the weather board (I originally matched the pins to the moteino so I could mount them) I'll just have to find a way to connect the battery charger (an adafruit lipo charger) - I did coat the weather board with some silicon conformal coating but not the shiny new moteino...
What are folks doing to protect their boards from humidity and shorts? Soldering the BME280 on the board took me many tries (and 3 BME280!) so I'm hoping I can get this right so I don't have to create another weather board :-)
Thanks in advance for any insights you may have,
X
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The only sure way that I know of is to encase your electronics in a waterproof and vaporproof potting epoxy and, if using batteries, use ones with tabbed connectors that you can solder directly to. Unfortunately, the epoxy is rather expensive.
Avoid encasing lithium batteries directly in epoxy though: they typically have failsafe vents as a fallback in case of thermal runaway, and you risk explosion if you constrain that.
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thanks for the reply - unfortunately the BME280 needs airflow so I can't really enclose everything completely - I think the breadboard was a bad idea, I'll move away from that. would heat shrink connection between a wire and the pin of my moteino be enough or should I solder the whole thing and then clear coat w some silicon?
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Why not store everything moisture sensitive in a food container that has a gasket seal, then store the BME280 board in another container that has free air flow. Create a hole for wiring and apply silicone to seal any gaps to the sensitive electronics.
Breadboard is OK for quick prototyping but is not a good idea even if air tight since the connections can become loose or oxidize etc.
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thanks for the reply - unfortunately the BME280 needs airflow so I can't really enclose everything completely - I think the breadboard was a bad idea, I'll move away from that. would heat shrink connection between a wire and the pin of my moteino be enough or should I solder the whole thing and then clear coat w some silicon?
Let's put it this way: have you ever used cabling that's rated for direct burial outdoors? The individual wires have insulation and then there's a layer of sticky goo to go around them to keep water and water vapor away from the regular wire insulation. That bundle then all gets encased in some kind of outer waterproof casing. If regular insulation were enough, then there'd be no need for the sticky goo. Now, your station isn't going to be buried underground, but over time the moisture will find its way through your heatshrink and/or wire insulation and probably cause corrosion. Enough to matter? Who knows? I suppose you might get some indication of that by looking at how professional grade weather stations have been put together and weatherproofed and take cues from that.
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thanks Felix for the idea - simple to try.
thanks for the thoughts whitehare - I've coated the BME280 board in silicon already, I think I'll go w Felix's idea of waterproofing the radio+battery and only have a couple of wires go to the BME board, I can put some silicon as well around the wire connections. All of this lives inside a Stevenson screen already, albeit a 3D printed one that looks cheap. I just bought last week an enclosing for a WS replacement so hopefully that one is better than mine and wont let too much water in...
thanks again for taking the time to share your thoughts
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If you're going to hermetically seal it's sometimes useful to have a 'pressure equalizer'. This is like a small balloon on the inside of the box that can expand or contract as the pressure changes outside. What happens sometimes is hermetically sealed boxes aren't really quite completely sealed, there are microscopic holes. If these holes get covered with moisture and the pressure outside increases the pressure difference can suck moisture into the box, this is a slow process but over many many cycles the inside of the box eventually becomes wet. The balloon makes sure the pressure inside the box is always the same as outside it.
Mark.
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perky: that's a great point and a good trick!
I got rid of the breadboard and used weatherproof connectors between the solar panel & the moteino. Applied a generous amount of silicon coating as well and put the solar charger and battery in a plastic bag that is "sealed". We'll see how long it works!
thanks all for the feedback and ideas
x
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Just to expand on that, you can get things called accordion bottles. They look like this:
http://www.leevalley.com/en/wood/page.aspx?p=20004&cat=1,110,42967
If you poke the neck through the side of the box so that the bottle itself is inside the box but the neck of the bottle is open to the outside pressure, then the bottle will contract or expand depending on the pressure difference. These things are sometimes called bladders. The only pressure difference remaining would be the compression or expansion pressure of the bottle, so choose one with low compression force and you're away!
Mark.
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One thing I'd point out as a chemical engineer is that the water vapor transmission rate across plastics is typically on the order of 10+ times greater than across aluminum or other metals. If one was trying to minimize moisture ingress into an enclosure, you would want to stick with metal as much as possible. Additionally, the use of a desiccant such as silica packets would also help minimize corrosion due to moisture in the local environment. Finally, the use of a spray applied superhydrophobic coating such as NeverWet could be a useful addition. These coatings are not very durable (despite the manufacturer's claims to the contrary) but while they remain intact, they are very effective:
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thanks for the note ChemE. I coated the board with some silicone (https://www.amazon.com/gp/product/B008O9YIV6/ref=oh_aui_search_detailpage?ie=UTF8&psc=1) - I'll try NeverWet next time though! (just ordered it from amazon)
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and just in case someone is interested, here are my findings:
- silicon conformal coating: my first try was to coat the board w silicon conformal coating, it worked for a while but when the first rain came my board short circuit (I think the issue was my solar panel connections though which were protected only by some hot glue which probably is porous) - silicon conformal coating leaves your board shiny...
- NeverWet: did 2 coats open boards and the solar panel, leaves an horrible white powder on the boards, thought it was busted after first rain - boards have worked great so far even after 3 days of rain - been working fine for 10 days now and battery seems to stay charged. Thanks again to ChemE for the idea, we'll see how long the coating works...
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I can confirm that hot glue isn't weatherproof. Despite what you might think, moisture gets through it and parts corrode.
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and just in case someone is interested, here are my findings:
- silicon conformal coating: my first try was to coat the board w silicon conformal coating, it worked for a while but when the first rain came my board short circuit (I think the issue was my solar panel connections though which were protected only by some hot glue which probably is porous) - silicon conformal coating leaves your board shiny...
- NeverWet: did 2 coats open boards and the solar panel, leaves an horrible white powder on the boards, thought it was busted after first rain - boards have worked great so far even after 3 days of rain - been working fine for 10 days now and battery seems to stay charged. Thanks again to ChemE for the idea, we'll see how long the coating works...
It seems there is a broad range of 'NeverWet' products, which did you use?
Tom
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Tom: I used this: http://www.ebay.com/itm/222031819453 - note that coat #1 needs/should be applied multiple times for optimum results
Please do note as well I think I may have been mistaken on the cause of my original issue (see comment on hot glue being porous) and that the silicon conformal coating may be enough (and not as messy and needing multiple coats). I have 2 soil sensors getting ready and I will try to see what the difference its between the silicon and the neverWet, I think I'm short a moteino though so this may take a couple of weeks to get the results...
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Please do note as well I think I may have been mistaken on the cause of my original issue (see comment on hot glue being porous) and that the silicon conformal coating may be enough (and not as messy and needing multiple coats).
Ah, yes, I did miss this comment. Thanks for following up. Of course, this now begs the question as to what you're using for the silicone conformal coating. I did notice that the NeverWet info on this particular product stated that it's not recommended for electronics or clothing but this may be related to the plastic housings of consumer 'electronics', not circuit boards themselves.
I have 2 soil sensors getting ready and I will try to see what the difference its between the silicon and the neverWet, I think I'm short a moteino though so this may take a couple of weeks to get the results...
I'm looking forward to your results!
Thanks again,
Tom
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With regards to waterproofing electronics, this might interest you :
where they demonstrate these and others (see the links in the video description).
https://www.amazon.com/gp/product/B0009H1AMG/ref=as_li_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B0009H1AMG&linkCode=as2&tag=flitetest-20&linkId=5IZ2HDR6RVOP4QIT
https://www.amazon.com/gp/product/B003HFTI0S/ref=as_li_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B003HFTI0S&linkCode=as2&tag=flitetest-20&linkId=NBC55OU5ZZYLPNHY
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@GregMo, very cool! Thanks for posting!
The next question, of course, is have you tried any of these on a Moteino?
It seems as if the liquid CorrosionX would be the most useful (and least messy) if you can just dip your circuit board and connectors into a bath of this stuff.
I'll be deploying some new Moisture sensors this spring, I'll be trying this out!
Tom
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I haven't had the chance to use those products myself as access for certain products is a bit harder here in SA (though i see they have a local distributor). That being said, the guys over at Flight Test (the vid above) are pretty thorough, and the long range telemetry equipment they use is very similar the the Moteino's and the RFM69's. I would be weary of using the products on items such as humidity sensors and various such sensors, but on the batteries and moteino's, it should be fine.
Greg
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Thanks again to ChemE for the idea, we'll see how long the coating works...
My pleasure! I've gotten enough help from the EEs that hang here, glad the conversation drifted near my discipline and I could be the one helping out.
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@GregMo, very cool! Thanks for posting!
The next question, of course, is have you tried any of these on a Moteino?
It seems as if the liquid CorrosionX would be the most useful (and least messy) if you can just dip your circuit board and connectors into a bath of this stuff.
I'll be deploying some new Moisture sensors this spring, I'll be trying this out!
Tom
Did you get a chance to try this stuff?