On 1/31/2017 4:02 PM, druck wrote:
> On 30/01/2017 20:10, The Natural Philosopher wrote:
>> On 30/01/17 19:19, Jamie Kahn Genet wrote:
>>> In this situation only practical solutions, are to outfit the Pi 3 with
>>> an oversize heat sink of the sort one might salvage from a desktop
>>> computer, or (since I desire a small case) a fan.
>>
>> well you could run the whole thing in a refrigerator.
>
> You jest, but I did that for a day while investigating the thermostat on
> the fridge. The wires to the waterproof DS18B20 temperature probes are
> quite thick, so would break the seal, but the Pi (original 256MB Model
> B) power cable is very thin, so I decided to put the whole thing in!
>
> I was surprised that WiFi still worked from inside so I was able to
> remote monitor it from another Pi, as well as logging to SD card. Taking
> readings every minute showed the cycling of the temperature and the
> effect of the door being opened. Having the whole thing in, also enabled
> me to use a temperature and humidity sensor which produced some
> interesting readings as humid air was cooled.
>
> But back to the subject; running the Pi at an ambient temperature of
> around 5C instead of 22C dropped it's idle temperature from 45C to 30C.
> In another experiment I left it in the car during a night where it got
> down to -5C but this only resulted in reducing the idle to 26C.
> Unfortunately I didn't try stressing it under these conditions, to see
> the affect on the maximum running temperature.

There would appear to be something wrong with your numbers.  If you
raise the ambient temperature 1 degree, the core of the CPU should rise
1 degree.  If you lower the ambient temperature 1 degree, the core of
the CPU should lower 1 degree.

Your first example is close enough it can be chalked up to measurement
uncertainty (electronic thermometers are not very accurate).  The second
example is hard to explain.  I suppose there could be some effect from
the air being dryer at temps below freezing and so not being as
effective at carrying away the heat.

--

Rick C

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