I'm trying to directly power a Raspbery Pi 3 by wiring it to the 5 volts rail of a power supply (5v to pin 2 and GND to pin 9), in this case a peripheral 4 pins connector. However, it never manages to boot (green LED blinking 3-4 times).

An ampmeter shows a current of 0.1A, which seems rather low, so that's probably the matter. I've tried connecting it to the motherboard ATX 20 pins and the floppy connector, but current is always limited to 100 mA. I thought that the problem could be that the PSU may not start properly without a big enough load, but even connecting it to a running PC hasn't changed anything.

Does anybody have any advice?

EDIT: after another test (I've removed the 5 volts fan from the raspberry) the red and green LED are costantly glowing)

  • "green LED blinking 3-4 times" -> If this is steady, even blink like a signal (as opposed to a flickering) it implies it failed to load firmware or the kernel from the SD card.
    – goldilocks
    Commented Feb 2, 2018 at 19:21
  • "green constantly glowing" -> It will do this if there is no SD card inserted, or the SD card cannot be read at all (due to an invalid partition table, etc.).
    – goldilocks
    Commented Feb 2, 2018 at 19:23
  • The blinking is regular (altough the last blink is shorter than the others) and the SD card is perfectly functional as it works perfectly with a normal usb poser supply
    – Mauro F.
    Commented Feb 2, 2018 at 19:36
  • Okay -- but that is what the blinking (or steady glow) indicates. It could be that it is not getting enough power to use the SD card properly, although in that case the red led would likely flicker.
    – goldilocks
    Commented Feb 2, 2018 at 20:26
  • Is the power supply powered up? In particular is the Power On signal connected to ground. See en.wikipedia.org/wiki/ATX#Power_supply diagrams for the 20 and 24 pin connectors.
    – joan
    Commented Feb 2, 2018 at 21:07


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