johny
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Location: Australia

Hot Pi! (A little bit of temperature testing)

Tue Jul 30, 2013 1:59 am

Hi all,

Since I spent a bit of time yesterday seeing how the Pi holds up in a sealed case in hot circumstances, I thought I'd post my findings here for others to benefit from too. I don't have any fancy pictures like those found over there, however, so you might find that post more visually pleasing.

Setup:
- Raspberry Pi B (we haven't got any model A's sitting around yet)
- Plastic shipping case from RS (the pink one)
- A DS18B20 temperature sensor for measuring the air temperature inside the case (just jumpered onto P1, including a pull-up)
- A heat source (in this case, an incandescent desk lamp at very close range)

I configured the Pi to log the temperature every few seconds both from the DS18B20 and the on-chip sensor (via /sys/class/thermal/thermal_zone0/temp). That done, it got sealed into the plastic case using electrical tape, making it effectively air-tight. The only connection to the outside world was the power lead. While it would have been nice to have had a remote console available to it to monitor the temperature in real time, I wanted to avoid loading the LAN chip at all as we're expecting to be using model A's anyway, and that chip has a considerably smaller temperature range (see the FAQ).

The Pi was then left to run for ~1h under the heat of the lamp. The outside temperature went up to 85C on the side facing the lamp, and ~40-45C on the opposite side, measured using an IR thermometer. This was more than I had hoped for/expected, and got me somewhat concerned for the welfare of the Pi. (Side note: 85 degree plastic isn't very pleasant to touch - guess what made me go looking for the IR thermometer...)

After the hour or so, the lamp was switched off and the Pi left to cool for a bit (and give it time to sync its logs to disk) before it was switched off. The resulting log was the plotted:
hot-pi-idle.png
Temperature graph, CPU idle.
hot-pi-idle.png (38.49 KiB) Viewed 2520 times
As can be seen, the air temperature inside the case went up to about 65C, and the core temperature nudged 98C, but seemed to stabilise at that.

A second run was then performed, this time with the CPU fully loaded:
hot-pi-fullcpu.png
Temperature graph, CPU fully loaded.
hot-pi-fullcpu.png (40.58 KiB) Viewed 2520 times
As can be seen, the temperature is actually noticeably lower this time around. Presumably the distance between the lamp and the Pi was slightly greater here, though the surface temperature again reached 85C. It's not all that surprising to not see an increase in the core temperature though, as others have already concluded that the CPU load does not really contribute much to the heat load (see link earlier in this post, for example).

Conclusion: even in the middle of summer here in Australia (where it can get up to 45C in the shade in my area), the Pi seems unlikely to face any issues, even if stuck in a sealed box outside, especially if it's not exposed to direct sunlight. Long-running tests would be needed to tell whether repeated heating/cooling would cause damage over time, but for now the results are looking good.

Conclusion #2: Don't use hot-glue in the case. The 65C was enough to seriously soften it back to a sticky state. (Side note #2: guess what else I touched?)

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Davespice
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Re: Hot Pi! (A little bit of temperature testing)

Tue Jul 30, 2013 9:26 am

That's a good bit of work. Nice one :) Thank you.

johny
Posts: 58
Joined: Tue Apr 24, 2012 10:00 am
Location: Australia

Re: Hot Pi! (A little bit of temperature testing)

Thu Aug 01, 2013 1:31 am

If there's a Pi fan in a testing facility that could put a Pi through its paces, or even someone in the manufacturing chain who could figure out what its limits are meant to be based on the manufacturing process, I'd love to see that. A former house-mate of mine used to work for a military equipment testing facility, but alas he's both changed jobs and fallen out of touch.

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rpdom
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Re: Hot Pi! (A little bit of temperature testing)

Thu Aug 01, 2013 4:06 am

johny wrote:If there's a Pi fan...
[ob rant]You don't need a fan on a Pi [/ob rant] :lol:

r1b4z01d
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Re: Hot Pi! (A little bit of temperature testing)

Tue Sep 10, 2013 2:48 pm

Awesome post, check out my finding pre and post heat sinks.

http://r1b4z01d.com/blog/1032/projects/ ... emp-tests/

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rpdom
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Re: Hot Pi! (A little bit of temperature testing)

Tue Sep 10, 2013 8:43 pm

r1b4z01d wrote:Awesome post, check out my finding pre and post heat sinks.

http://r1b4z01d.com/blog/1032/projects/ ... emp-tests/
Thank you for that post. I now know that I really do not need a heatsink on my Pi :-)

r1b4z01d
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Re: Hot Pi! (A little bit of temperature testing)

Fri Sep 13, 2013 11:06 pm

rpdom wrote:
r1b4z01d wrote:Awesome post, check out my finding pre and post heat sinks.

http://r1b4z01d.com/blog/1032/projects/ ... emp-tests/
Thank you for that post. I now know that I really do not need a heatsink on my Pi :-)
No problem, I wouldn't say it's absolutely required but for the price of them is silly not to.

edit: http://www.amazon.com/National-Power-GS ... s=100Ah+6v Maybe this

technoducky
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Re: Hot Pi! (A little bit of temperature testing)

Mon Sep 16, 2013 11:42 am

I never understand why people feel they need to put heatsinks and fans on the Pi.
The Broadcam IC is designed to run at relatively high temperatures in embedded applications without a heatsink, and the linear regulator would never get particularly hot since it is protected by the ployfuse.
In fact by putting a heatsink on the Broadcom IC, all you are really cooling is the memory, as the cores are on the side of the chip nearest the PCB.

It's good to see someone actually do some testing about temperature limits rather than instantly slapping a heatsink on every package they can see and shouting "FIXED!".

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