On Fri, 09 Sep 2005 04:39:29 GMT, Ignoramus965
wrote:


I am hoping that I can get some help from learned and esteemed experts
here... Doubtless, I could not undertake this project alone. I hope
that there will be people who may take enough interest to stop me if I
do something stupid. I am not really afraid of, say, losing $80 that I
would spend on components that blow up, although I would prefer not to
endanger anyone's safety.

I already did many interesting things by "standing on the shoulders of
giants", such as repair of a diesel generator or building of a phase
converter etc. I am saying this not to brag -- these were relatively
simple things compared to electronic design issues that some of you
are experts in -- but rather to underscore that projects can be brought
to successful completion with a bit of care, open mind and good advice.

A bit of care, an open mind and good advice won't suffice here,
particularly if you selectively ignore the advice. Those who do
things like this successfully have had to study, why do you think that
you can skip it? Vastly superior intellect perhaps?

Some of your questions have been answered more than once, with
consistent advice that perhaps you think you can regard as "optional".
It is, of course, optional, but the results are predictable -- and
have been predicted consistently if with varying degrees of color
and emphasis.

The topic of switching high currents with solid-state devices is far
too complex to cover with answers to a few specific questions. I
think it is presumptuous of you to expect many folks to spend time
responding to isolated questions in preference to your doing the same
homework they/we had to do in order to be able to answer your
questions -- not homework specific to your questions, but to
learn the technology. There are textbooks. There is a wealth of
application notes from various semiconductor fmrs. There are
courses and seminars.

You have been told about MOSFET drivers and high-side drivers several
times. You persist in wanting to just use a sig gen. So do it!
You have been told about inductive power sources at least twice.
You were told about MOSFETs -- so you proposed IGBT's.

This does not suggest "inquiring mind" to me; it suggests lack of
discipline and perhaps laziness, lookin' for a back door, a shortcut,
the "easy way". There is a reason engineering is called a
"discipline".

I would like to see some evidence that you have spent some of *your*
time at serious study and lab (bench) work yourself before you ask
further questions of this incredibly willing and often eager group.
I think it's fair, and a reasonable courtesy to ask. You'll need
to research your own questions a bit if you're to understand the
answers -- and the (many) other relevant questions you probably don't
yet know you should have.

Anticipating a possible 30-second response of "Thank you, and what
might those questions be?", I can only say the myriad of questions
those skilled in the art have forgotten they once had while staring at
a charred spot where a transistor used to be. (BTW, the T in MOSFET
stands for transistor....) "Those skilled in the art" means we
dumb**** drones that did the homework and learned the technology.
You don't have to do all of it, but you do have to do some. It's a
tiny subset of electrical engineering. Nearly all who work with power
elex are mostly or entirely self-taught in that specific field, using
the same resources I've recommended to you.

Questions that might be more productive for you, when you're ready to
ask them, might more like "here's what I did, here's what happened,
what did I do wrong?", followed by "OK, I did what you suggested (if
you really did), here's what happened ......" and so on.

If your objective is simply to have a welder, then I'd strongly
suggest you find a good bargain and buy it. You do seem to be
skilled at finding bargains. The engineers at Lincoln and Miller
are not idiots. If a squarewave addon box could be done for a buck,
they'd be doing it for a buck and selling it for two. They've spent
most of two decades learning to apply power electronics to welding.

Then, of course, you'll want to learn to weld......