> It probably did seem a bit strange. Basically, I need to
> make a power supply capable of around 100v @ 30A. It does
> not need to be regulated, but should be well filtered as
> it will be in a solid state 1.5kw PA. I have selected
> some components, but it is all subject to change as I am
> having a tough time finding a transformer at a reasonable
> price for the project. I have even thought about not
> using one! I found these squar d electrical transformers,
> and thought that they might work for what I wanted to do.
When people make line isolation transformers or control
transformers they use the smallest amount of copper they
can. The resistance of the winding limits peak current. The
power factor will kill regulation with a capacitor input
supply unless the transformer is sized for the largest
possible wire size and has a good core selection.
When you use a choke input like you are planning things are
much better, but now you have to find a suitable 30A choke.
You should use a transformer for a few reasons (as was
already covered) like line surges and safety. It is against
code to EVER ground a neutral to anything connected to
something external, so the neutral has to float. You could
float the entire negative rail from chassis, but then the
issue becomes spikes from the power line into the PA and
harmonics from the rectifiers into the power mains. You
certainly could design a system that would use the power
mains safely and not break codes, but it would require some
care.
The real problem is knowing the ESR of the transformer.
Certainly it isn't as low as it could be because of the fact
it is a control transformer, but a choke input would help a
lot. You could get a power factor close to unity rather than
the very poor power factor of a capacitor supply, so you
might be OK if the choke is a good one.
73 Tom
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