For my Raspberry Pi B+, I have a 5V 5A adapter.For the adapter though I had to cut and connnect a micro usb cable (to power input of RPi) and another cable to the power outlet (kind of and industrial adapter i think so i needed to do the wiring myself). Now eventhough everything works OK, ( I have two RFID readers and a QR reader connected to USB ports along with relays, buzzer, temperature sensor etc. to GPIO pins) the PWR LED is not on. With a different adapter (5V 2A) I get a always on red PWR LED.

Is PWR LED not being on indicates a problem? or is this simply an issue of me being not able to connect micro usb cable properly.

On a side note if I get always on PWR LED with 5V 2A adapter, I think I don't need a 5V 5A is this correct?


1 Answer 1


The power LED being off indicates that the Pi voltage is less than 4.65V.

That's not a problem if everything is happy with the power it is getting.

I'd just take it as a warning to expect a crash if you stress the Pi or add further components which need power.

  • I thought that blinking led indicated voltage is less than 4.65V. I also have a crappy adapter that caused the power led to blink and system was unstable and all the components kept restarting. In any case, is it safe to assume if the power led is steady, system is stable electrical wise?
    – saccu
    Mar 9, 2016 at 11:52
  • @ickarsim The power LED will blink as the voltage drops beneath and rises above 4.65V. Yours must always be beneath 4.65V. You need a meter to check.
    – joan
    Mar 9, 2016 at 12:27
  • ok thank you. I'll just ditch problematic adapter and use the stable one.
    – saccu
    Mar 9, 2016 at 12:37

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