08-23-2006, 08:13 PM
[quote Racer X]FYI, the spec for FW is 12v 1.5 amps MAX per bus, and for USB 2 is 5 V 2.0 amps MAX per bus. So that is 18 watts for FW, and 10 watts for USB2.
That's why I use only FW bus-powered drives.
But what really matters is the per port power, the spec calls for only 500 mA. So that provides only 2.5 W to a device on that port. Some designs allow a bit of cheating and "steal" a bit of the total power available on the bus and give it to one port, but that is not part of the spec. So if the device calls for more than 500 mA, it may get it on some USB ports, but it is not guaranteed to work on another.
That's why I use only FW bus-powered drives.
But what really matters is the per port power, the spec calls for only 500 mA. So that provides only 2.5 W to a device on that port. Some designs allow a bit of cheating and "steal" a bit of the total power available on the bus and give it to one port, but that is not part of the spec. So if the device calls for more than 500 mA, it may get it on some USB ports, but it is not guaranteed to work on another.
