Ping: Iggy

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 to ripple.

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 consuming.

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.

i

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.

Thanks,

Jon

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 learned something.

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.

Jon

Look at the manual of Miller Syncrowave 250. I believe that it includes an intelligible schematic and uses SCRs.

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?

Jon

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.

Jon

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 Rec.Crafts.Metalworking.

The price is not negotiable, as the scrap value of copper in there exceeds the above amount.

i

Thanks, Iggy. Digging around more it does seem to be common on some TIG machines; I will go with this.

You have mail.

Jon

Jon,

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 site:

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.