Power the Pi from the USB (rather than the micro-usb)

[liyou.zhou]

I am using a powered usb hub and I found that the pi can work even when the microusb power cable is not plugged in. Presumably it is using the power from the usb hub through the actual usb port. Why should the pi behave like this? Is it safe to just do without the micro usb power?

[RaTTuS]

yes / no depending...
back powering will bypass the fuse on the RPi
if you have an early one then it will probably not be able to supply enough backwards
later RPi's will be able to be powered this way - you should not power from the micro USB and the usb at the same time

[Lob0426]

If your USB hubs PSU provides stable power then you will be just fine.

It is true that back-powering a Raspberry Pi, through the USB, bypasses the fuse. So does powering a RasPi by the GPIO.

As Rattus said, if you have an earlier Rev. 1.0 board it will not work properly back-powering. A Rev. 1.0 can be modified to work well. i have two that run this way. A Rev. 2.0 board back-powers just fine with no modifications.

My web site has several articles on back-powering a Raspberry Pi if you want to run your board this way! My web server is back-powered and has ran stably and reliably for over a year now!