On Aug 16, 3:09 am, " wrote:

So if both the 12V and 5V need the same reference then could I connect
V- on the 5V PS and the V- on the 12V PS and the ground on the AC side
of the 12V PS all together? Are there any safety issues with this?

You have already stated that with the 12V supply, V- and AC-ground are
connected? That is, you did what Phil suggested and looked for
continuity between the -12V and AC-ground?

Keep in mind that some (cheap) power-supplies use autotransformers,
such that the LVAC side is still directly connected to the AC mains...
meaning that the DC side also remains connected to the AC mains.
Others use step-down transfomers with the secondary isolated from the
primary. You need to determine which is which in your case. More work
with the VOM, but easily determined.

Unless both supplies are isolation-type and writing for myself, I
would not connnect the two together without further testing for
potential between the two, or between the workpiece (what you are
powering) and the two if connected together. If they are isolation-
type, then there should be no safety issues.

But test for AC and DC potential between the two supplies anyway
before making any common connections.

Next question: Does the 12V supply have enough capacity that you could
use it to provide 12V and 5V via a divider?

Peter Wieck
Wyncote, PA