I am in the process of converting my buzzbox to something resembling a 150A
TIG supply. I already have the AC-DC section figured out, as well as the HF
I believe you used SCRs in a circuit you used to control the output current
of one of your machines, and I am very interested in this. Do you by any
chance have a schematic of this section of your circuit, and/or any other
reference schematics of going about this topology for a high current supply?
Thanks for your help,
What is your OCV?
Jon, I have some documentation along with parts pictures, sample
welds, etc, here:
If your welder is single phase (mine is 3 phase), it changes a lot due
All together, this was a moderately expensive project and I would be
better off just buying a nice welder. It was fun, but very time
I also post the source code of my welder, written in BASIC, here:
It is under GPL, so feel free to do whatever you want with it, as long
as you keep it free software.
80V on the low range, for AC. I'll probably lose a bit after it goes
through the bridge.
Sure, thanks Iggy. I forgot yours was a three phase sysem, which does shift
things around a bit. I'll look through the page you provided, that looks
like a good place to start.
Another point is, SCR driver boards are expensive. I was very lucky in
that for some readon, PCTI liked my kids site algebra.com so much that
they donated a SCR driver device to me, which was easy to use.
Still, I would be far better off applying my efforts elsewhere,
wotking less hours, and buying a great new welder. That said, I
Those are some good points you make there. I guess what I am trying to do
is use a handfull of discrete componenets to make as simple of a
variable-current supply as I can get away with. Perhaps the only way to
control the current is with a highly-advanced topology, utilizing complex
circuit boards, but if there is a way to do it with a minimum of components,
then I am going to try to do this.
I guess what I really need is to look at a schematic of a transformer-based
TIG supply that used SCRs to control the output current, and see how they
did it there, but I don't know the name of any units that used such a
control method, much less have a schematic.
Aye, thanks Iggy, that is a readable schem. It looks like they are using
the SCRs in place of the bridge for controlling the current, but are using
an IC (or another unspecified group of components) to drive the gates.
I wonder if there were any TIG supplies that used a more simple method of
controlling the current, maybe in the pre-IC days?
Yes, that's why you need an SCR controller to go with the SCRs.
Don mentioned another method. I do not recall what it is.
This is a project that I am kind of happy that it worked, but I regret
starting it, the time wasted, etc.
Thanks Iggy. I am going to build this myself (with some assistance from
those more experienced, of course), using available discreet components
(maybe an IC if there is a compelling reason), without purchasing any
pre-assembled circuitry or boards. This will entail building my own
"controller board" to control the SCRs, but that's part of the fun, too!
Before I can do that, however, I need to first determine the topology that
is used in this type of circuit (silicon control of current in a welder). I
am hoping I can come across an early TIG supply schematic that will give me
clue as to what methodology was used, be it pre-transformer control or
post-transformer control. That's where I'm stuck at right now.
IIRC, he mentioned he would use IGBTs, but I think that might be more
complicated than I am williing to go, at least at this stage. SCRs don't
seem too terribly complicated for me, it's just finding out the layout of a
basic welder current control to give me a place to start that is my obstacle
right now. Eventually there will be zero-crossing detectors, but one step
at a time.
The topology is that of a regular rectifier bridge (1 or 3 phase), but
with SCR instead of diodes.
The SCR drivers need to do a lot of things.
I have a big SCR assembly for sale. $100 plus shipping for
The price is not negotiable, as the scrap value of copper in there
exceeds the above amount.
I too am trying to do this except I already have a AC/DC Tig welder
with high frequency. Its an Lincoln Idealarc 300 and does not have
true squarewave. All I want to try is to generate a squarewave output
w/ variable frequency (20 - 300 Hz) So what I am going to do (or at
least try) is to take the DC side of it and run it through an H bridge
using 4 IGBT's. I will drive them similar to the circuit at this
It might be along the lines of what you are trying to doing. I give
credit to Iggy, he too has invested a lot of time into this.