I'm having an issue with my Pi 3 regarding power/heat issues.

I have a setup where a UBEC has been powering a Raspberry Pi 3, 5in HDMI touchscreen, and small fan for a project. It was running fine with temperatures measured from vcgenmd measure_temp being less than 70 .

Recently, the Pi would not boot even though the UBEC was still giving power to the screen. I opened the case it was in, and plugged power into the UBEC again. I thought I saw a faint curl of smoke and smelled a faint burning smell but I inspected the Pi and UBEC and they all looked good.

I booted the Pi 3 again without the extra screen and case and used it for 2 or 3 hours using a 5v 2A power supply I had. It worked fine but there was a solid rainbow square in the corner so I decided to power the Pi with the UBEC again over the GPIO like in the previous setup.

I did this and the Pi booted, but after about ten minutes it started rebooting continuously and the UBEC light flickered of and on. I tried powering a Pi 2 and Pi B+ with the same UBEC and it worked perfectly. The UBEC is rated at 5V/3A and 5A max. I tried different cards with different OS's that I knew worked in the other models and the Pi 3 would sometimes boot but always start rebooting after max 10 mins.

At one point it would not boot being powered with 5V/2A supply or the UBEC. I let it alone for an hour and then it would boot again, but I had the same problem after a couple of minutes.

All I can think of is some fuse on the Pi, that won't let it boot if its too hot and I should just wait a day or two before using it again? Any ideas what might be the problem? Thank you in advance.

  • "All I can think of is some fuse on the Pi, that won't let it boot if its too hot and I should just wait a day or two before using it again?": It's called a polyfuse but it is bypassed if you were powering via UBEC -> one of the 5V pins. I do not know if these symptoms are consistent with it being "partially tripped" (or if that is possible), but if you suspect it has let it be for 24 hours before you apply power again. Perhaps you have damaged the 5V regulator -- or the 3.3V, if you were powering via a pin. :(
    – goldilocks
    Jun 17, 2016 at 18:45
  • @goldilocks For sure I didn't wire the UBEC to the Pi incorrectly, how else could it have gotten damaged? I will wait 24hrs before I try it again for sure. Its brand new though so I am anxious to no what I could be doing wrong. The UBEC I am using is this one which 3 or 4 other people were using for there Pi's too: https://www.amazon.com/Ship-Hobbywing-Switch-mode-UBEC-Lowest/dp/B008ZNWOYY/184-6311376-4670407?ie=UTF8&*Version*=1&*entries*=0
    – NULL
    Jun 17, 2016 at 18:52
  • I didn't say incorrectly. I said if you power it via a 5V pin, you bypass the polyfuse and the regulator, so it better be a pristine supply, and not one that may, e.g., lead to current surges if too much is drawn on the circuit momentarily and then voltage drops, then the load drops. That's the kind of thing a regulator protects you from, I think -- but I'm not an expert and could be confused about these matters ;/. Anyway, point being it's not an issue of hooking it up incorrectly, its about the risks involved when powering via the 5V pins.
    – goldilocks
    Jun 17, 2016 at 18:59
  • @goldilocks Oh! Now I am a little worried that's what happened :(
    – NULL
    Jun 17, 2016 at 19:03
  • BTW: Based on the specs of the UBEC I would have assumed all this should be fine too. But again, I lack the experience to say for sure. Hopefully you don't end up chalking it all up to that...
    – goldilocks
    Jun 17, 2016 at 19:04

1 Answer 1


After letting the board alone it still would not work.

Moral of the story: if you are powering your pi over the 5v rail be very careful and don't assume anything.

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