On Tue, 08 Aug 2006 13:21:34 -0700, zekor wrote:
Mark Fortune wrote:
Greetings to the collective.

For my next project I want to build a bench power supply and do away
with this old switch mode AT computer PSU that i'm currently using.

The design I have in mind will be pretty beefy, giving a wide range of
fixed and variable output voltages (i'm thinking from -50v up to +50)
and deliver up to 5amps of current. if my estimates are right i'll need
a 600va+ (100v * 5a + overhead) transformer to do the job well. Now i've
had a look at some transformers in this range, and they're a little out
of my price range. so now i'm considering building my own.

The specifications I need are as follows:

primary: 0-230v @ 50Hz
Secondary: 60v-0-60v
secondary output current max: 5A

I have an intermediate understanding of transformers, but have never
actually built one, hence I am seeking advice from those with experience
in this field.
So where do I start? what type of core is best for this application? - I
have a friend who's blasting off that toroids are best, but i'd like a
second opinion, and what kind of wire to use for the primary and
secondaries? what are good safety practices regarding insulation? Is
this even a feasable project to undertake (moreso on the money side than
timewise). Any other advice also greatly appreciated.

I would recommend reading up from every source. I have built torroids
using the winding which was orginally a variac. These were 110 volt
units. You automatically have a primary so all you need to do is wind
the secondaries on top. I have also done the other type of transformer,
schelacing.the iron plates. I would also recomend what others have, buy
surplus on the market. Combine transformers if you can't find them.


I used to work for a battery charger manufacturer who made their own
transformers. They had a machine to stack the lams, alternating, of course,
and a big machine to spin the bobbin while the guy hand-wound the windings
on it. Then, when it was all stacked, they'd whack it to make sure all of
the lams were as tight as they could get them, bolt it up, hypot it, and
then bake them and dip them in hot varnish.

BTW, I don't think there are many USENETizens who would consider
themselves part of any "collective" - that's the Borg. =:-O

Good Luck!
Rich