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RPi Compute module high temperature operation

Former Member

Hello,

Hi, I am working in a prestudy project where we are looking at using the Raspberry Pi Compute Module in a building automation application.

We have difficulties finding info about temperature behavior.

 

Is there an absolute maximum rating specified for the Broadcom chip or the module as such?

 

What happens to the functionality of the chip when it reaches high temperatures? Are certain functions disabled? Does it shut down?

 

Any input appreciated.

 

BR Pål Dahle

 

 

 

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  • 0

    There are some numbers here, https://www.raspberrypi.org/forums/viewtopic.php?f=98&t=74908

    looks like 80 degrees C is the limit.

    Approaching such a temperature, the Pi 3 reduces the speed of one of its clocks in an attempt to reduce heat.

    I don't know how intelligent the throttling is, whether it examines the CPU load before performing this.

    The compute module may do something similar. I'd strongly suggest you try it, and not just rely on

    information that is out there, because things can change from release to release. A change in speed can

    be severe for an embedded app, so you don't really want to be at the 80 degrees C point.

    Anyone want to put hot air onto their Pi, see what it does w.r.t. throttling? Could be interesting..

  • 0 in reply to shabaz

    I don't  think the throttling depends on anything but temperature.

     

    The main question to Pal (I have tried copy-pasting into this window to spell that correctly, but some fancy Farnell-stuff blocks that... sorry) is: what is "high temperature".

     

    If you want it to run at 100 degrees ambient... 100% certain: you can forget that.

    If you want to run it at 40 degrees ambient... 100% certain: sure you can! But the throttling may happen earlier than you might expect, and it would be good to keep in mind that the CPU might start to throttle when it hits a heat-limit. If the throttling is bad for your application, you may need cooling measures. If you require maximum performance, you'll further heat up the CPU by having it DO stuff, and the throttling may happen at an inopportune moment....

  • 0 in reply to rew

    Yeah I suspected as much : (

    It was interesting to see the Pi 3's behaviour where it seemed to toggle between a few (seemed like 2 or 3)

    values under certain conditions to try to and cool off (see graphs below). Whereas some Intel chips drop and then ramp up. Probably there are patents in some of these implemented strategies I guess.

    Some article (anandtech, usually has more information but not this time) suggested that some mobile processors by Intel

    can have different strategies depending on additional information like orientation, and seems to use a power sensor too.

    Anyway, for compute module Pål, ( I had to go into HTML mode to do that with å, couldn't find another way ),  make sure your software engineers are aware that throttling could occur if you determine that the temperature and amount of processing could result in this. They will need to test the application under such speed conditions (more relevant for the compute module than an app for a PC or tablet/mobile phone).

    image

  • 0 in reply to shabaz

    I'm amazed over the lengths you go to spell my name correctly! Appreciate it image

     

    The CM will sit in an enclosed box on an application specific I/O board. The box will sit in some sort of chamber that in itself can be exposed to sunlight, India is a potential market (they recently had a temperture record of 51 degC...). This hw spec says +60 degC ambient right now (and I currently work with our customer to get more accurate data, I suspect it was set ad-hoc with some margin, to maybe get it down to 50-55 degC). I have myself been running the RPi A-version for long periods in a very lightweight application and it seems self-heat about 25-30 degrees, (as expected rather independent in a 5 degC - 30 degC ambient temperature span).

     

    So in essence we are on the limit for "high temperature" :-)

     

    The application (as it is defined today) require very little from the SW, wouldn't be suprised if we were below 10% CPU load on average. Throttling is not a problem the way I see it. I'm not fully clear whether the CPU will switch off at high temps (did I read that somewhere here?).

     

    We will be running some tests for sure, to check the behavior, both on hw-level and on system level (if we ever get that far... :-)

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