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Power circuits from PC componenets
by Acidus at 4:12 pm EDT, Oct 12, 2004

] USB connector is designed to feed power up to 100 mA 5V
] power to the devices connected to it. The power is fed
] though Vbus and GND pins. The host USB pert can supply up
] to 500 mA at voltage at least 4.75 V (for the HUB to be
] able to power 4 port HUB which can supply up 100 mA at
] voltage of at least 4.40V). The USB port does not need to
] supply more than 100 mA unless the device connected to it
] requests more current. UL overcurrent-prevention
] requirement says that no USB port ever pass more than 5A
] onto any port (short circuit protection to avoid damage
] to equipments and wiring).

Reference to myself: Check effect on other USB devices when sourcing ~2A.

RE: Power circuits from PC componenets
by Decius at 4:32 pm EDT, Oct 12, 2004

Acidus wrote:
] ] USB connector is designed to feed power up to 100 mA 5V
] ] power to the devices connected to it. The power is fed
] ] though Vbus and GND pins. The host USB pert can supply up
] ] to 500 mA at voltage at least 4.75 V (for the HUB to be
] ] able to power 4 port HUB which can supply up 100 mA at
] ] voltage of at least 4.40V). The USB port does not need to
] ] supply more than 100 mA unless the device connected to it
] ] requests more current. UL overcurrent-prevention
] ] requirement says that no USB port ever pass more than 5A
] ] onto any port (short circuit protection to avoid damage
] ] to equipments and wiring).
]
] Reference to myself: Check effect on other USB devices when
] sourcing ~2A.

Most USB ports won't give you the current you're looking for. They simply aren't designed to draw it. You'll either brown out the USB network or your power will simply shut off.