|Check the drive label It should show there. For example, I'm looking at an old 20 gig western digital. It shows 0.80 amps at 5 v DC and 0.45 amps at 12 v DC. Now, that's for the entire drive but the motor is going to need most of that. And that would be a maximum spec.|
Yoiu can always bust open an old drive and see if the power requirements are shown on the motor itself. I'm not sure but maybe the 12 v is principally for the motor and the 5 v is for the electronics.
And, you know, volts x amps = power
Now that's what I call a sticky situation