I've just bought my rpi b+. Power supply for raspberry is 4.94V (which is in appropriate 4.75-5.25Vrange).

Raspberry pi working good, but there is one possible trouble. I don't know why, but power led (and rainbow square at top right of display) randomly blinking (approximate 1 blink for 30 seconds-1 minute, there is no direct dependence). Does this behaviour of raspberry pi is normal? What are possible causes for this issue?

UPD: I've noticed short blinks are usually coming on specific actions, like opening a new tab in the browser


Your power supply is on the edge. It is just enough for your normal usage but as soon as you add any additional stress on the CPU (opening a tab) it starts to fail.

Plugging in a USB device will probably have the same effect.

Put up with it, or buy a power supply which provides more amps (say 1.5 at least) at a stable 5V.

  • joan, my power supply provides 2.25A.
    – asiniy
    Feb 24 '15 at 8:30
  • @asiniy No, it does not, otherwise you wouldn't be seeing the errors you are.
    – joan
    Feb 24 '15 at 8:46
  • is there a chance that trouble caused by jack from power supply or by usb cable? I use power supply - usb jack - microusb cable to send power to my RPi
    – asiniy
    Feb 24 '15 at 8:57
  • The wires in USB cables can be very thin. It's certainly worth trying a different cable. If you have a meter you could (carefully) measure and check you have 5V between pin 2 and pin 6 of the expansion header (pin 2 5V, pin 6 Ground).
    – joan
    Feb 24 '15 at 9:22
  • 1
    That's fine. The warning kicks in when the voltage drops below 4.65V. For an unregulated power supply the voltage will drop at higher loads.
    – joan
    Feb 24 '15 at 11:18

My problem was in weak usb cable. I plugged more powerful usb cable to solve this issue

  • What is a "weak" usb cable?
    – Bex
    Feb 24 '15 at 15:21
  • @Bex The opposite of a strong one ;) This is plausible; the problem might not be the supply but a cable between the supply and the device.
    – goldilocks
    Feb 24 '15 at 15:39
  • @Bex, goldilocks right. Cable can't provide a lot of power from power supply to raspberry.
    – asiniy
    Feb 25 '15 at 5:50
  • @Bex Narrow wires = high resistance = voltage drop across cable
    – Basic
    Oct 11 '16 at 14:10
  • In my case I bought a bunch of USB cables from China that have switched near the device end, and as soon as I threw it away and put in another the problem went away.
    – SDsolar
    Apr 17 '17 at 7:40

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