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underwhelmd
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Cold Pi

Sat Dec 30, 2017 2:47 am

We had a cold night Wednesday into Thursday morning. This is from a Pi Zero W that has a camera and a ds18b20 temp sensor attached in a box outside. Around 6am Thurs the cpu reported it was at 3.5C with an outside temp of -16.8C.

That is the coldest I've seen MY Pi(s) run so far. I'm hoping to see 0C or less in Jan or Feb. This Pi has no USB drive attached for storage, just runs off the microSD card.. A USB drive is good for +8C difference inside the box.

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W. H. Heydt
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Re: Cold Pi

Sat Dec 30, 2017 2:54 am

There was a penguin observing experiment using Pis in Antarctica. They recorded temperatures below -42C. (IIRC, the system failed...when the batteries froze.) Your Pi is in no danger of failing due to low temps.

Paul Hutch
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Re: Cold Pi

Wed Jan 03, 2018 2:49 am

I left one of my Pi Zero W nest cams up and running, it failed at about -18°C/0°F ambient last week. Considering it's made from consumer grade parts I consider that acceptable behavior as most consumer grade electronic parts are only rated for operation to 0°C/32°F. If I need a circuit to work below freezing I design it with parts rated for below freezing, or build in a heater to keep it within spec.

Of course if you have a housing that helps hold in heat (my Zero W did not) and/or get lucky with the parts in your specific units it can certainly operate at much lower temperatures. The specification of minimum operating temperature is a guarantee that it will always work down to that temperature not that it will fail at that or any specific lower temperature.

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underwhelmd
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Re: Cold Pi

Wed Jan 03, 2018 3:50 am

I'd like to know what exactly failed on your Pi at that temp. Seems a bit pre-mature for cold alone to have done it... was there moisture in the enclosure?

Paul Hutch
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Re: Cold Pi

Wed Jan 03, 2018 3:40 pm

Don't know what caused it to fail yet. I plan to power it back up once the temperature gets back above freezing. I suspect it will work again as that's been my usual experience with consumer electronics that failed while being used outside of the normal consumer electronics parts specified temperature range. I've been designing consumer & industrial electronic products for a living for over 35 years now so I've seen lots of this type of failure in many products and even more products that kept working even though they were not rated to work below freezing.

The Pi Zero W is only in the foundation case on a porch so it effectively is directly exposed to outside temperatures. It was running fine right up until about three days in a row of -18°C low and -10°C high temperatures. This was after about a full week of never getting more than a degree above freezing and accompanying ultra low %RH so it's extremely unlikely for there to have been any liquid water around. It's predicted we'll get above freezing for two daily highs in about 5 days.

Being a nest cam I didn't bother to add any protection to keep it running after the birds migrated south. When I build my general purpose nature cam I plan to use a sealed box so that the heat of the Pi 3B inside will help keep it above freezing. On really cold days I'll have a wasting CPU cycles task run to increase the CPU heat and if that isn't enough I'll add a small heater (power resistor).

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DougieLawson
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Re: Cold Pi

Wed Jan 03, 2018 3:47 pm

Do something useful to warm up your RPi3 like building OpenCV or the Linux kernel (with make -j6).

Running a soaker seems like a waste.
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underwhelmd
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Re: Cold Pi

Wed Jan 03, 2018 3:59 pm

I think your Pi was a victim of moisture because of that case it was in. I hope it revives.

I use various sizes of these "waterproof" enclosures from chinese sellers on ebay. I'd buy local but the price is 4 times the ebay cost. Several have been outside for over a year.

This one is good for a Zero with some accessories and a cam. This particular Pi doesn't have a USB flash drive and the CPU is typically reporting -8C less than the same configuration but with a USB flash drive for storage. So a USB flash drive adds quite a bit of warmth to an enclosure.
Image

This one is good for a Pi 3 size Pi with accessories and a cam.
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Paul Hutch
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Re: Cold Pi

Wed Jan 03, 2018 4:06 pm

underwhelmd wrote:
Wed Jan 03, 2018 3:59 pm
I think your Pi was a victim of moisture because of that case it was in. I hope it revives.
Extremely unlikely, bordering on impossible, to have moisture problems this far bellow the freezing point. If there was going to be moisture problems I would have expected seeing them sometime in the previous 8 months when it was above freezing and often at nearly 100%RH.

Paul Hutch
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Re: Cold Pi

Tue Jan 09, 2018 6:46 pm

Temperature finally got above freezing yesterday so I powered it back up. Everything is working perfectly AFAICT. Reading through the logs it appears the WiFi was all that stopped working. Judging by the -30°C rating for the WiFi IC I suspect it was simply a matter of the Xtal and/or capacitors being far enough out of spec due to the the sustained -10 to -20°C ambient temperature.

Now that I know that only the WiFi had stopped this time, I won't power it down if it goes silent again. I'm interested to see if the WiFi comes back on it's own when the temperature recovers to sane levels and if any other sub-systems stop.

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