"Ignoramus8187" wrote:
For your question regarding TIG welding, I would say that if you can
replicate capabilities of a Syncrowave 250 DX, you would do very
well. Miller has the specs and manual available online.

Thanks for that, Iggy. That manual has some good expalations of the TIG
process, as well as the schematic, which is very informative for me.
The schematic, however, is bringing up a question in my head. For DC usage,
it is pretty straight forward; xfmr, SCR bridge, smoothing choke, and that's
about it.

For AC, however, they are doing something I haven't come across before.

(here is the relevent section; work is green, electrode is RED, and blue is
the (+) and (-) output from the SCR bridge:

http://home.comcast.net/~danniken/Sy...DX_Page_60.png

if it wraps: http://tinyurl.com/48bzgn

Now, the work goes back to the transformer, no surprises there, but the
electrode does something odd. It goes to the part of the bridge where AC
normally goes, and the DC outputs of the bridge are connected through the
smoothing choke!

What the heck?

They also have this going to the DC output from a diode bridge, SR2 in the
schematic.

Now, I haven't seen this topology before, but in the absence of a later
inverter, I have to assume they are using the SCR bridge (and possibly the
diode bridge) to modulate the AC waveform somehow.

Any ideas what this is doing, or even what it is called? Maybe they are
doing this to avoid having to have a transistor/mosfet inverter after the
rectifier, I dunno. Sure is compelling, though.

Thanks again,

Jon