A toutes fin utiles :
Source : http://elinux.org/RPiconfigUSB Power
max_usb_current
Together with the raspberry PI B+ a new config.txt setting was introduced.
max_usb_current=1
when adding this line the USB power manager will change its output current limit (for all 4 USB ports combined) from 600mA to double that, 1200mA.
max_usb_current=0
is the default, and limits the USB current to 600mA.
Make sure your power supply (and microUSB cord) are up to the task of delivering the extra 0.6A current.
PS : Non encore testé.