On Sun, 23 Apr 2006 15:24:02 GMT, Ignoramus17838
wrote:

On Sun, 23 Apr 2006 14:27:51 GMT, Glen Walpert wrote:
On Sat, 22 Apr 2006 20:58:04 GMT, Ignoramus8092
wrote:

Thank you Guy. My plan is as follows: wire the transformer as three
phase Wye, and use three SCR half bridges in a scheme similar to that
by PCTI. These three half bridges will be added without disturbing
current SCRs.

I have six secondaries, two on each leg, I will parallel each pair.

Does it make sense?

i

No. Wiring the transformer as (a single) Wye requires having access
to all 6 secondary leads on each transformer half (12 secondary leads
available vice the 6 I think you actually have) so you can reverse the
phase on one half (switch the neutral connection with the 3 line
connections on one side) so they can be paralleled. This will totally
screw your existing 6-phase rectifier of course. I suggest you
re-read the description by Lawrence of how the 6-phase system works
(previously posted to ABSE).

Glen, I have physical access to all 12 leads: I have three legs, two
secondaries on each, and two leads on each secondary, all plainly
visible and physically accessible.

Some secondaries are connected in parallel to form the existing "6
phase rectifier", but I could disconnect them.

Here's the schematic of my welding xfmr:

http://igor.chudov.com/tmp/firing/xfmr.jpg

Here's its actual pictu

http://igor.chudov.com/tmp/firing/welding-xfmr.jpg

Right now, the following points are connected:

A3, B3, C3;

A2, B2, C2;

These connected pieces are connected to the interphase transformer.

I want to rewire it by disconnecting A3, B3, and C3 from one another,
and by connecting

(A3, A1); (A2, A4)
(B3, B1); (B2, B4)
(C3, C1); (C2, C4)

Then I will have a common point of (A2, A4, B2, B4, C2, C4); and the
wye leads (A1, A3), (B1, B3), (C1, C3).

Is this wrong?

i

That is the correct way to rewire the transformer secondary as single
3-phase Y (and not what I thought you were planning), but I thought
you said you wanted to leave your existing 6-phase rectifier connected
and operational, and rewiring your transformer as 3-phase will
preclude that. This also gets rid of the current balancing action of
the interphase transformer, which is of course completely
disconnected.

Why not use the installed rectifier as wired, and build a new
controller for it, adaptable for either CC or CV? If you have
problems you can just reconnect the original controller.

If you are willing to abandon the existing rectifier entirely then
transformer rewiring and a standard 3-phase SCR rectifier module
should work. But it seems like the hard way to do the job to me.