| Electronics > Beginners |
| Designing for extreme temperatures: -50°C to +50°C ambient |
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| RyanT:
I've never had to design anything to run in less than 0°C ambient or more than about 50% RH, which certainly made things simple. Project brief: I want to add some custom smarts to my garage, car, and porch. Where I live, this means -50°C to +50°C ambient, and humidity from 0-100% RH (usually well below 50%), with temperature swings of up to 30°C overnight. Nothing directly exposed to the elements. Nothing mechanical, aside from a few buttons. All circuits below 14VDC, and low enough power that passive cooling should be more than adequate. Most of these would be either mains rectified or battery powered, while at least one would run off of car wiring. Expected lifespan would be a few years at <1% duty cycle. In other words, not setting the world on fire (pun simultaneously intended and not). Cost considerations: these are one-off fun projects, so I'm not trying to shave pennies off of the BOM by any means. I realize the "correct" answer to my implied question is "duh, read the datasheet!", and of course I will when it comes down to it, but more specifically, I'm looking for higher level, rule-of-thumb type observations that apply most of the time. Acceptable battery chemistry, component types to avoid (I'm looking at you, standard temp. range LCDs!), PCB layout considerations, use (or not) of potting compound, enclosure considerations, that sort of thing. I also realize that, in some respects, designing for cold temps is very different from designing for hot, so if you have expertise in one but not the other, please share what you know. :) |
| MosherIV:
Hi You are pretty much looking at the kind of design used for military electronics with your -50°C spec. I can pass on some techniques. Choose hermetically sealed aluminium encloses. Choose components rated to high temps (50°C is actually not that bad for mil spec) Mount components/boards so that they use the enclosure as a heat sink. Most people do not know that some mil spec equipment use built in heaters to cope with low temps. Use heaters (power resistors) where components are not rated for below 0°C Use conformal coating to seal boards against moisture. You will get condensation inside your enclosure! You will get condensation inside your enclosure even though it is sealed (yes, I repeated myself becuase it is that important). Use mil spec circular connectors. They are guarented to be sealed against moisture. Use any other type and you will loose the seal the enclosure gives you. Be warned, they are EXPENSIVE. So use sparingly. Hope that helps. |
| voltsandjolts:
^ what Mosher said...and don't use any batteries or displays (other than LED) and you'll be fine! |
| Rerouter:
If your using a microcontroller, be aware RAM can take many minutes to clear at significant negative temperatures when power is disconnected / interrupted, so be sure to clear and initialize any relevant registers on every start up. equally capacitors can get weird, most datasheets dont go that low, |
| Ian.M:
Specifically any wet or gel electrolyte capacitor (e.g. Aluminium or wet Tantalum electrolytics, and supercaps) may be be damaged by -50°C, and ion mobility in solid polymer electrolytes is likely to be so much lower at -50°C that the ESR will dramatically increase. |
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