Maker Pro
Maker Pro

Sharing power supply across electronic devices


Ian Clowes

Jan 1, 1970

I have a device with a 2.5" IDE laptop hard disk in it. I temporarily
want to put a 3.5" device in there, just for a few hours.

I can sort out the data signalling using adapters I have, but also
need to power the 3.5" drive.

The target box has 5V for the laptop drive, but doesn't have a 12V
line as needed by the 3.5" drive. I don't want to alter the PSU to
add one at present.

Q: Can I run the drive from the power supply of a nearby PC without
any problem?

These are the issues I can think of...

1) AIUI, a 3.5" IDE used 12V for drive power, and 5V for logic.
Should I use the target device's 5V to ensure the data levels are OK
at both ends? I would then use just the 12V from the PC supply.

2) Should I tie the chassis and/or 0V lines of the two PSUs together
for any reason?

3) I have a spare PC chassis around that I might use. I read
somewhere that the PSU needs a minimum load to keep it sweet. Is this
true? If so can I just leave the motherboard connected without
worrying whether it actually boots, etc?


Ben Weaver

Jan 1, 1970
Hi Ian...

In my experience:

1. Doesn't matter who supplies what, as long as 5V gets 5V and 12V gets
12V - bearing in mind that...

2. Tie the grounds together. Otherwise one might float.

3. Yes indeedy. Just shove a mobo or spare hard disk on any PSU to keep
it happy. Might not turn on otherwise.

*ALSO* make sure you turn all the PSUs on and off at the same time. I
find that HDDs don't like having 12V with no 5V and vice versa.

Have fun...