What does the 4 wires in a HD power plug do?

[BlueSteel54]

Could someone please explain why a hard drive has 4 wires in the power plug.

 

[Freestone]

+5V (Red), Ground (Black) +12V (Yellow), Ground (Black)

http://en.wikipedia.org/wiki/Molex

 

[edfair]

The why is to keep the small changes in current flow (therefore a voltage shift in the ground) in the motor circuits from getting reflected in the control circuits.

And although the Wikipedia article calls it a Molex connector the specifications for this on earlier drive manufacturer spec sheets are for an AMP connector (AMP Special Products--a TYCO subsidiary). Molex now provides a comparable product.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[BlueSteel54]

Thanks you

So you are saying that the hard drive actually uses 2 differrent voltages. A 5v and a 12 v and that 1 black wire is the ground for the 5v and the other is the ground for the 12v. That the ground wires are isolated from each other.

 

[edfair]

They are come from a common solder pad in the power supply.

Ed Fair
Give the wrong symptoms, get the wrong solutions.