I'm using an old power supply unit from an old computer (2011 HIPRO) to power my Raspberry Pi.

I have measured the voltage across the terminals of the 5v output (Red and Black) and have proceeded to hook this up to a USB adapter which goes straight to the Pi.

My problem is that using this PSU the red "on" indicator light does not turn on, versus when I use a USB charger it does.

Was there a problem with this red light not turning on? Is this bad for the Pi?

BTW everything works fine using both power supplies, the Pi turns on and the screen is shown, able to login etc.

Please see my photo of my setup below:


Closer View of the PSU pin outs:


  • Have you tried turning it off and back on? – user38639 Dec 23 '15 at 9:32
  • Which model Pi. Is the red light which is not on a Pi light? – joan Dec 23 '15 at 9:32
  • The model is RaspPi 2 Model B V1.1 (2014) and it's the main light next to the GPIO pins, it is on the Pi. – James Marino Dec 23 '15 at 9:37
  • When you say "I have measured the voltage..." what exactly was it? And what is it at the pi now? (Use a lead from the 5v pin and a ground, be careful not to short these) – goldilocks Dec 23 '15 at 10:48
  • The Red LED being off indicates the PSU voltage is not enough. You could have problems if your Pi does not demand enough power. PC PSUs are pretty much always "Switching-Mode" and the behaviour of those can be less than ideal if their minimum load is not being demanded - can you post the label of the PSU with the load details on it. Also - how did you tell the PSU to come out of "standby-mode" - is that the other wire looped back on the connector? – SlySven Dec 23 '15 at 20:13

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