On Wed, 27 Apr 2005 20:05:51 -0000, "Dave" wrote:

it is possible as long as both output terminals are isolated from the line
ground (and case preferably for safety!). many dc supplies connect the
negative to the case and line ground so if you tried to put them in series
you would short one of them out through the other one's ground.

"Richard" wrote in message
news:teAbe.436$3V3.55@edtnps89...
Can someone tell me if it is possible to hook up two 12 Volt DC power
supplies in series to increase the voltage, I have two supplies that I
would
like to do that with , one being a variable supply. I need About 25 volts
total.
Any info on this is greatly appreciated.

Richard

I am reminded of a day in our engineering lab at Westinhouse Ordnance
Department in 1958 when I was working on the depth control system for
the MK-45 (ASTOR) torpedo.

Everything aboard the fish ran on 24 volts for a variety of reasons -
tradition, it was readily available as a tap off of the main battery,
and there was a host of 24 vdc electrical equipment available from the
war years.

We had a 24 vdc motor generator set in the lab that produced all of
the 24 dc main power to the workbenches in the lab. Each workbench had
a pair of wires coming to it with a large two-pole knife switch to
connect or disconnect the 24 vdc source.

Each person working at a bench was generally engrossed in his own
private hell of trying to make whatever he was working on work
properly. As you might expect, no one paid much attention to how his
circuitry was grounded locally - if at all.

One day a lab technician named Mike working a couple of benches away
from me started laughing about the smoke that he saw rising up from
the circuit on my bench. I felt rather stupid about the fact that for
some reason my circuitry was cooking, big time. Then I noticed that
behind Mike there was a column of smoke rising up from his circuitry,
as well.

You guessed it, he had the negative side of the system grounded at his
bench and I had the positive side grounded at my bench. We had a
general meeting shortly thereafter.


Bob, W9DMK, Dahlgren, VA
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