On Tue, 02 May 2006 14:49:35 GMT, Glen Walpert wrote:
On Mon, 01 May 2006 02:24:49 GMT, Ignoramus19383
wrote:

Glen, I put together the most basic configuration, and voila, the
controller did produce the voltage that I expected. No current tests
yet, but that the voltage was correct, makes me think that everything
is alright. Now that I know that it is working, I will actually wire
it up properly, that will take quite a while to get all the copper
wiring, contactors etc, right.

I am now going to ask about making a plasma power supply.

A little update, I took out the old rectifier from my Cyber Tig, which
freed up a lot of space, for a nice installation of isolated case dual
SCRs.

I will hopefully install the heatsink and SCRs in a couple of days. It
will need some brackets to fit into the space available.


Sounds good so far. Do you have a MIG torch for testing under load
yet?

No, all I have is TIG equipment...

An alternative to transformer reconfiguration with a bunch of large
contactors would be a patch panel with the transformer windings and
load connections brought out to studs on an insulating panel, with
copper bussbar links and a few jumper cables able to switch to any of
the 5 configurations (6-phase, and 3-phase wye and delta both with
series or parallel winding connections). Compare the time difference
in assembly with the likely time spent changing configurations, and of
course parts on hand ...

Well, I already bought five 50a contactors for $9.99 each. I drew some
schematics, they should be enough to switch between parallel delta,
vs. series wye (for plasma).

I am going to start with wiring for just welding (parallel delta), and
make the welder part work fully. I want to move in smaller steps.

After that, I will add contactors to switch between parallel delta,
vs. series wye.

When connecting transformer windings in parallel it is always a good
idea to connect one end first, power up and check the voltages between
the unconnected ends, which will not only let you know if you have a
winding backwards without letting any smoke out, it will show any
winding imbalance with the correct connection, which should be very
small.

Great point, I will do just that.

Do the same thing with the delta connection, first connecting
the 3 windings in a U configuration and checking voltages between the
open ends before making the final delta connection.

This is a very nice idea, I was quite afraid of this delta connection,
but this is a safe way to go.

If there is a significant voltage present (more than a few percent
of phase voltage) then check for circulating current at no-load with
an amprobe or shunt when you make the connection. Since it is not
an always-on power dist transformer you could live with some
circulating current; eg 10% of rated current circulating still
leaves 90% available for welding and my hunch is it will not be that
high, what there is will tend to equalize phase voltages, and it is
just part of the cost of using unbalanced power from your rotary
converter.

Yes. Also, I want to finally make the transformer switch on when I
need to actually weld. It should not be on all the time, like it used
to be, it is a waste of electrons.

(BTW I think it is considered poor netiquette to stick a persons name
in a message subject line, even though it is done all the time. Glen
or GW would be better than the full name in caps if you want my
attention, but I tend to keep an eye out for your project so you could
put that in the body and I would still probably notice.)


Sorry about that Glen, I changed the Subject of this post.

i