[Milsurplus] LV Supply...

[J. Forster]

Rick Brashear wrote:

> Thanks to everyone who helped with my low voltage supply dilemma.  I
> tried the bucking transformer idea and it worked great, I should have
> remembered to try that, but old age is creeping in and brain power is
> creep out.  I don't have a transformer with a high enough amperage
> rating to leave in circuit, but I'll get one.  Peter, since you were the
> first to suggest that let me ask you.  Is there any difference in using
> the "bucking" system to reduce primary voltage than there is using a
> variac?

Not really. You need to make sure the buck transformer is sized right...  both
as to secondary amperage and watts.

> And, do you think feeding the primary with less than its
> designed voltage will have any adverse affects?

Your losses will be a bit bigger, but as long as the transformers  are sized for
your load, you'll be OK.

> My personal thoughts
> are the bucking transformer is more like adding primary windings to the
> original transformer, but I could be looking at it wrong.

Not quite, but close enough. Adding turns or reducing the applied voltage, both
reduce the peak flux density in the core, and reduce the output voltage. The
slightly larger wire size in the primary, compared to a winding with more turns
on the same core, will reduce the copper loss a bit. BUT, you have the losses in
the other transformer. Don't worry...  be happy.

FWIW,
-John

> I appreciate each and every suggestion, they were all certainly a
> solution.  I do have a couple of variacs that would work, however, they
> are both quite large and would be difficult to incorporate.
>
> Thanks again to everyone for your help.
>
> Rick