Hi Guys,
i always use cheap aliexpress Arduino Nanos for my projects.
But now i actually have to make 20 small devices that have to work in an outside environment (in germany: -15°C(5°F) to 30°C(85°F)). They should work at least a few years.
These are the parts i need, everything x20:
1x 220V Relay controllable with Arduino Signal (example)
or instead of arduino+relay: ESP+Relay Combo (example)
So i am looking for advice for reliability for these devices, since i don't know a awful lot about microelectronics.
My guess would be that the relay will survive, the Arduino nano will maybe survive, but the powersupply will fail. Is this true? What are my other options? How do i keep costs down but still get good parts?
Any certified (SGS, TUV, Intertek...) USB power supply capable of supplying 1A is going to fit the bill. As for the relays, go for the known brands such as Omron and such.
As for the outdoor enclosure, any IP54 rated enclosure suitable for outdoor use (mind UV radiation!) is going to be fine. If you have to add cables to the enclosure make sure to use the correct cable glands that do not compromise the IP rating.
If the devices are situated far away from houses and/or near industy, it might be wise to look into additional surge and EMC protection.
Corrosion caused by moisture condensation and current flow between conductors is a very difficult problem to solve and it is almost impossible to keep moisture out of an enclosure, even if it is very carefully sealed.
For any circuitry that will continuously be exposed to the outside atmosphere and temperature swings, you must have all circuit boards and wired connections "conformally coated" to seal everything. The coating is similar to fingernail polish.
Otherwise, count on at most 1-2 years before failure.
I would try sealing it air tight, and putting some silica jell in the housing. The seal is important as it warms up and cools down the air in the container will breath unless it cannot get out. You could also submerse it in oil, there is special formulations for electronics.
You didn't say what those devices have to do. How far apart, how exposed, etc. Those things matter. You're mentioning 220V supply - that implies always on, for me that also means fully sealed boxes (which is nigh impossible!) are out, inverted buckets are in. Just have a few big holes in the bottom of your container to let air in and out, moisture and all, and easy access for wires. You may want to add some fine mesh there to stop critters from taking residence.
Moisture will not be an issue as the always on electronics will heat up the inside to a few degrees above ambient. That's all it takes to keep things from getting wet. A spray of conformal coating does the rest, I've had stuff working that way for a few years in a climate that's routinely at 100% humidity for days on end, not protected from rain or wind, in boxes that cost me less than 2 Euro a piece.
For power supply: consider a 12V supply that you keep indoors, then using regular mains wires (nice and thick, well protected from the elements) to bring the 12V to your devices; each with a 12V-5V buck converter. The 12V so you don't need to care about wire losses too much (those buck converters don't care if they get only 10V, to name something extreme), and to lower the current by just over half. Also keeping 220V away from your own contraption is just plain safer, and you don't have to worry about thoroughly waterproofing the power adapters.
Sealing a box is very very difficult, especially if you want wires to go in. That's a great channel for moisture to get in - if not along the outside, it will go through the inside of the cable!
Miracollix:
1x 220V Relay controllable with Arduino Signal (example)
That relay is - just a relay.
You cannot just connect it to an Arduino, you need a transistor to drive it (with a current-limiting resistor to the base) and a reverse diode across it. Or a relay module.
If you are powering from mains, a Nano is fine. If you were powering from a battery, the USB interface chip is an unnecessary current drain.
Is there a cheaper + smaller alternative?