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

2 Answers 2


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. Commented Feb 24, 2015 at 8:30
  • @asiniy No, it does not, otherwise you wouldn't be seeing the errors you are.
    – joan
    Commented Feb 24, 2015 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 Commented Feb 24, 2015 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
    Commented Feb 24, 2015 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
    Commented Feb 24, 2015 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
    Commented Feb 24, 2015 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
    Commented Feb 24, 2015 at 15:39
  • @Bex, goldilocks right. Cable can't provide a lot of power from power supply to raspberry. Commented Feb 25, 2015 at 5:50
  • @Bex Narrow wires = high resistance = voltage drop across cable
    – Basic
    Commented Oct 11, 2016 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
    Commented Apr 17, 2017 at 7:40

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