u need to be running a solid state HDD it will only take a shock on a write cycle to screw your hole HDD something like
this (will also lower boot times) its a tryed and tested normaly HDD's dont work
as for the power, PC's will eat power just like amps all depending on spec of PC but look
12 watts/12 volts = 1 amp
(and your PC more like 300watt)
300 watts/12 volts = 25 amp
Hope this helps Tom