I am getting my RasperryPi Rev2 soon, and I plan to use it as a media centre. I have a WesternDigital Elements 1TB USB3 2.5" USB powered external harddrive. I know that a normal USB port outputs 500mA, and the Pi recommends 700mA in.
I was wondering if I bought a 1.2A PSU, will that be enough to power the external through the RPi's USB ports?
I was looking at this power supply.
Micro USB power supply adapter,Euro,1.2A
Thank you for your help.
The 500mA is for USB2 (max of 5 loads of 100mA), this drive is USB3 (max of 6 loads of 150mA = 900mA).
External drives often have a (Y or chained) cable that connects to 2 USB ports to get the power needed. Check the specifications of that drive very well before buying anything.
A second reason why that adapter is too tight fit is the surge current (inrush current), a lot of power (relative) is needed to get the disk spinning inside, his is only for a short moment, but in this short moment the current is high, the voltage level might collapse to such a low level that the RPi starts to act weird, or just reboots.
The most safe option is to power the RPi with a separate supply and connect the drive through a powered USB Hub. This ensures that the RPi will not have to deal with any effects from power fluctuations from external devices.
The USB ports on rev 2.0 no longer have the silly poly fuses, but the power to the ports still goes via the main polyfuse.
Increasing the powersupply isn't a great idea, because of this polyfuse and also because it exceeds the specs of the USB socket the PI uses for power.
You should either use a powered hub (yuck) or splice the power cable to the drive (also yuck as this defeats the original purpose of the polyfuse)
