On Oct 3, 11:51*pm, terry wrote:
On Oct 2, 11:37*am, wrote:





On Oct 2, 4:29*am, raypsi wrote:

On Oct 1, 12:55*pm, terry wrote:

We recently modified such a power supply to get a single 12 volt DC
output at about 20 amps for a particular, amateur radio application..
In order to do so we had to load one of the 5 volt outputs with a
couple of amps in order to get the unit to work; but that's normal.

Hey terry

I did that very same thing loaded the 5volt with 5ohm at 5 watt.
Ran my TenTec 526 off the 12 volt side of the PC power supply.
I thought it was the sweetest thing since sliced bread. Then
people started telling me I had this strange background noise.
They asked me what was going on in my shack. I had this strange
eerie noise in my shack, so they thought. Wasn't in my shack per
say but it was the PC power supply. Nobody knew I was running
a PC supply to power my rig.

73 OM

n7zu

I also use a modified PC power supply with no problems. I did add a
filter removed
from a commercial computer SMPS. I don't know the values of the
components but its a Pi filter
and the inductor is wound on what looks like a ferrite rod. The caps
are some pretty big disk
that had the writing rubbed off of them a long time ago. As Grumpy put
it. I like to "Frankenstien"
some of my projects.

I have been giving some thought as to what it would take to modify a
PC power supply for HV use.
I have been thinking along two lines,

1 Connect a second step-up transformer before the rectifiers.
2 Replace the transformer with one with a HV winding putting a 5volt
winding on the new
transformer for loading and feedback.

Jimmie- Hide quoted text -

- Show quoted text -

Great info: Thanks for all the ideas and especially about the warning
that the HV would be on the line side (input) from115/230 volt mains.
Unless a 60 hertz full isolation transformer were used; the weight and
size of which sort of negates the idea of using a lighter weight SPS!

I too used to fix TVs without power transformers, using selenium
rectifiers (boy could they stink!) and voltage doubler circuits to
provide B+. That was back in the mid late 1950s. I also made up a
little B+ power supply in a box clipped in during house calls to show
a customer that the problem was indeed inside the chassis and it had
to be taken away for a 'bench job'!

By that and means of never charging for a house call if I didn't fix
the set in situ; built up a reputation for straightforward dealing
which, despite the slightly funny accent of a British immigrant to
Canada, some 15 years later, may have helped me become elected to the
areas first town council? And that in a day and age when TV repairmen
didn't have the best reputation in the world (well at least around
here) for ethical dealings!

These days customers are a lot more cynical and questioning; and
rightly so!

BTW first heard about SPS in the telephone industry, before PC were
common; when power supplier representatives started telling us about
'rectifier/power supplies' that had efficiencies of over 80%.- Hide quoted text -

- Show quoted text -

The 300 volts you wanted is on the input side of the power supply, not
what you wanted. This does not mean that the output of the power
supply is not isolated from the mains. The type of switching power
supply you wanted is probably doable. Think about removing the output
transformer from a PC power supply and connecting it back to back with
the transformer in a working power supply. The output could be
rectified and filtered and you would have a cheap to free lightweight
line isolated HV power supply. I am in thr process of trying this. I
not getting much work done on it due to my present work schedule but
in a few weeks things should get back to normal and I will have a
chance to play with my toys some more.

I am just getting in to SMPSs and find it amazing what these things
willl do.
For example I found a a +- 15 volt unit that puts out 100 amps for
each voltage. I can hold the output transformers in my hand, they
couldnt weigh more than a pound each.

Jimmie