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Author Topic: Raspberry Pi 3 seems to be on the way  (Read 4101 times)

NewtronStar

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Re: Raspberry Pi 3 seems to be on the way
« Reply #15 on: March 03, 2016, 08:05:46 PM »

This is an interesting Web page that discusses the CPU thermals on the new RPi3

http://makezine.com/2016/03/02/raspberry-pi-3-not-halt-catch-fire/
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sheddyian

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Re: Raspberry Pi 3 seems to be on the way
« Reply #16 on: March 03, 2016, 08:40:00 PM »

This is an interesting Web page that discusses the CPU thermals on the new RPi3

http://makezine.com/2016/03/02/raspberry-pi-3-not-halt-catch-fire/

That's interesting; I saw a page of thermal images on the day Pi 3 was launched (possibly the ones being referred to here) and it was indeed showing the CPU running at just over 100C.

It's claimed that the processor will throttle to keep it below this even under 100% load.

I've just been watching the latest "Bilge Tank" youtube, from Pimoroni who do all sorts of Raspberry Pi (and others) accessories, they were showing a Pi 3 running a stress test and testing it's temperature.


It's 50 minutes long and rambles a bit, but I rather like it.

In summary - they got it up to 100C without a heatsink but it was throttling it's clock speed to stop itself getting any hotter.  A heatsink dropped the temperature a fair bit.

My Pi 3 (under moderate load in desktop right now) is running at 55C without a heatsink.

Ian
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sheddyian

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Re: Raspberry Pi 3 seems to be on the way
« Reply #17 on: March 09, 2016, 01:43:29 PM »

I've been doing a bit of tinkering with a Pi 3, both with and without a heatsink.  My pi 3 correctly throttles when it gets to around 80C, as such I never saw the temperature rise much above 83C.

Looking at different articles, I notice different ways of measuring CPU clock speed, and I think that might have caused some confusion.

Either of these commands shows you the current CPU speed.  If the Pi is fairly idle, it'll show a lower speed, if the processor is busy, it'll show it runnig at top speed.
Code: [Select]
cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq
cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq

BUT it won't show the effect of CPU speed throttling when the CPU is getting too hot.

To see that, you need to use this command
Code: [Select]
/opt/vc/bin/vcgencmd measure_clock arm
I wrote a short script, called Check.sh, thus :
Code: [Select]
cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq
cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq
/opt/vc/bin/vcgencmd measure_clock arm
/opt/vc/bin/vcgencmd measure_temp
cat /sys/class/thermal/thermal_zone0/temp

I then set sysbench running in the background, loading all 4 of the Pi 3's cores.

Code: [Select]
watch sudo ./Check.sh

let me watch the CPU speed and temperature climb.

Although I didn't plot or record the temperatures, I can confirm that :

Without a heatsink, the Pi 3 will quickly reach 80C under full CPU load (constant 100%)

With a heatsink, it takes longer to reach 80C, but will still reach it under constant 100% load.

Once the temperature reaches around 80C, the CPU frequency does get throttled back to prevent the temperature rising much higher.

With a desk fan positioned about a metre away blowing air in the Pi's vicinity, the Pi 3 with a heatsink never reached 80C under constant 100% load. 

So in extreme cases perhaps a heatsink and a fan would be useful, athough it didn't seem to need much airflow to cool it.

But, realistically, is your Raspberry Pi 3 going to be under constant 100% CPU load?

I'm currently using the Pi 3, with the heatsink, NO fan, overclocked to 1300Mhz  ;D , and the temperature is hovering around 56 - 60C.

Ian
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