GPU/CPU temperature limit for RPI3

[jamesh]

I'm guessing (and this is purely guessing) that your voltage regulator is reaching its thermal limit and shutting down.

It's only the Ethernet failing, so not that.

[Pete6]

That was a good guess and nearly right. Over the decades I have learnt that the more attention I pay to power the better my project turns out. This was the case with valve amplifiers in the 1960s and it is still true today.

I have my Pi connected to a wired Ethernet and since it is a Pi 3 it only uses 4 of the 8 CAT5 wires for communication. Wishing only one cable to go into my outdoor case I fed 12VDC up the blue/whit and brown/white pairs into a buck regulator inside the case and from there I derive 5.5VDC for the Pi. I know the voltage is okay because the Pi is not complaining. So then I hit trouble and jamesh says

Odd. The Pi should simply slow down if it hits 85, not crash. Something is not right. I assume you are not overclocking?

Pi3 should be capable of running at well over 100 without failing (we make sure they don't though). I think we test to 120 or so in an oven.

Now I had never really suspected the Pi at all. I was certain that this was something that I had done either environmentally or with wiring so I looked really closely at my wiring. The image tells the tale. https://photos.app.goo.gl/EURFtQytAPYV5SXZ8 and proves my earlier point about power.

I have now removed the power from the RJ45s and use them exclusively for signal. I opened up the cable after the RJ45 and soldered a barrel connector to the blue/white and brown/ white pairs and plugged them back in. Inside the case the power wires are soldered to a PCB.

Both devices have come back up and have not failed throughout today but neither have hit CPU 85C either.

Moral: Do not feed power through RJ45s EVER. I should know better after the decades I have been doing electronics. I have now ordered some six pole (s'all I need) weatherproof connectors and will fit them when they arrive. As a temporary measure I have used DB9s.

Thanks to everybody for your help.

If anyone is interested, here's the entire project https://photos.app.goo.gl/kCZFW5AQyCtS55vf7

[magnesium meteorite]

I have built a small wooden enclosure for 3raspberry pi. The enclosure has a small fan and is open on 3 sides.

On one of the three PI, I have installed a HAT sound card. I have installed a small heat sink on the CPU.

The PI model 3B only runs OSMC, primarily for movie playback. I never overclock. I never watch TV or play video games or other fancy stuff.
One PI is never used, a Pi2B runs OMV, 95% of the time it serves movies to the OSMC system

After about 20 minutes, the thermometer comes on the TV screen and flashes continuously or semi permanent.. The OSMC/Settings/System Info shows 153 F.

I suspect that due to the HAT and the way the PI is oriented in the enclosure means the fan doesn't provide much assistance.

Unless essential I really don't want to start messing around with the enclosure. Due to lockdown its impossible for me to buy/beg/steal any new equipment like install a new small USB fan.

So I have two questions:

How much should I panic about the high temperature? I don't want to cause a fire.
Would buying the two GPU licences help to offload some of the processing? Fwiw, I never noticed a performance problem with the currnet setup, other than the temperature