When I'm using my RPi 3B powered by the micro-USB port (5V 2.4A) and I happen to use a USB extender for the power cable, the RPi 3 seems to boot up and work fine except for the fact that the red light simply goes out after successfully booting, with the green light still functioning properly. I can still use the console perfectly and do whatever I want like compiling with GCC and using peripherals.

When I don't use the USB extender cable, the RPi 3B's red light stays on forever while it functions, as expected? Note that the USB extender cable I am using simply lengthens the cable distance, it does not inject power and is USB 2.0. I think I may have ruined an RPi 3B by doing this, as a short while afterwards I had to buy a new one, as my old one refused to read the SD card and was stuck with a non-blinking red light. Typically a sign of death in my experience. I tried it on my new one once and it did the same thing, although it hasn't stopped working (yet?).

Can anyone explain this phenomenon? I've never heard of a Raspberry Pi 3 Model B still working and functioning seemingly perfectly without a red light. I feel like this is surely damaging the board? Whatever the answer may be, I'm staying away from the extension cable.

  • I have a Pi 1b where the red light is barely visible and just feebly blinks once a second. Regularly does 100+ days between reboots. Got it into that state flashing a PIC chip over the GPIO, no idea what it's taken against. Green light works fine. Been like that for at least two years now.
    – tobyd
    Dec 19, 2017 at 23:54

1 Answer 1


The cable has excessive resistance (in fact almost ALL USB cables have resistance which are too high but using an extender pushes it over the limit). See Raspberry Pi Power Limitations for more detail.

In fact the Pi, itself, will run quite happily with low voltages (down to ~4V) as it runs from 1.8V, but peripherals probably won't.

  • Seems to make sense, the only peripheral attached was a power hungry wifi adapter that's quite large. Still odd how it killed one of my RPi 3B boards.
    – RSS
    Dec 20, 2017 at 23:32

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.