Tested my TIG inverter bridge under full power

Congratulations! Was that 199 A into a short or into an arc?

Thanks... It was into a short. To have a welding arc, I would need to put the bridge to the proper place on the commutator.

Congrat's. I'm wondering if you came across any schematics of commercial tig inverters during your hunt? Or are they drawn as black boxes? Thanks, Jim.

Thanks. I may try to weld aluminum this weekend.

I have not found anything.

The only thing that my inverter does not have, is control of power when electrode is negative, and separate control when electrode is positive (I think that it is called AC balance). For my inverter, the absolute value of the voltageand current is the same for positive vs negative half cycle.

Basically, I think, commercial inverters are a lot like mine, they have a timing circuit, drive circuit, full bridge driven by FETs (MOSFET or IGBT), a snubber (maybe) and controls.

I am just a chump who put together my first electronic contraption, so I may not know as much as more learned members of these newsgroups.

Take my answer for what it is worth.

What is wrong behind my idea to switch the bridge asymetric? For example

Nick

This isn't much of a schematic. All the circuit boards are just rectangles. Also, this is a DC only welder.

Jon

It is a AC/DC welder. Look at FETs T21 and T22, you can see that they can be used to supply either +, or -, or +/- to the line labeled

in AC mode, I think, only one half of the secondary winding is working. I may be wrong, I slept only 3-4 hours for the last 2 days and am barely thinking, .

You can also see RCD snubbers near T21 and T22.

Certainly looks like an AC/DC welder. One good hint is the AC/DC selection switch in the lower-right corner (after rotating the page so it is readable).

The right-hand side shows two DC supplies, one + and one -, that are selectively connected to the "+" output via the transistors T21 or T22. They could be controled to give DC+, DC-, or AC.

It would be interesting to know what parts they are using for the IGBTs and the T21, T22 transistors.

I agree, except they appear to be bipolars, not FETs.

I think you are wrong. The tapped secondary is connected into two full-wave rectifiers for the two supplies (+ and -). Both halves of the secondary are always working, but only one supply (+ or -) will be connected at a time and supplying current.

Could be. I thought that bipolar transistors are also field effect transistors, that's why I said so. I am an amateur.

Exactly what I was trying to say, not so well.

They control balance with duty cycle control, which you can also do. Start with 50-50, or maybe 60% SP (electrode negative) and 40% RP (electrode positive). Practice with that until you can make consistently good welds. With only 200 amps max current you'll be limited to fairly thin aluminum, maybe 1/4" max. I'd suggest starting with 1/8" material. Don't blame the machine if you don't achieve instant success. A lot of excellent aluminum TIG welding is done with straight AC machines. When you can lay a stack of dimes in aluminum, then you can start tweaking the dutycycle or AC balance to optimize penetration with just enough RP cleaning to do the job.

I've followed this saga with some interest, will be interested in your results. I've thought about doing something like that for years, but have never been motivated to do it because I've been satisfied with the results I get with straight AC.

I can control the period of TIME when voltage is positive, or negative, as percentage of the cycle.

I cannot make the CURRENT or VOLTAGE on positive or negative different.

Yes, but, I think, they could also make current different for positive vs. negative part of duty cycle.

Yes, that's what I will try.

Yes.

I changed my mind and will not try actual welding, until I get the snubber circuit fully completed. There is just too much at risk and it would be stupid to ruin the machine just because I want to take too much risk.

It should be easy and fast for you, I suppose. It was fun for me, the cost was some low hundreds of dollars. In terms of time spent, it was very time consuming. If I used that time to make some part time income, I could earn enough to buy a brand new advanced Miller welder.

My plan now is to perfect my snubbing circuit. i

That's what I meant.

That's clear. But if you average the current flow (better to say polarity) and do not have a 50:50 cylce, you will have a DC-offset. Imagine having a 100:0 cyle. It would give you DC with one polarity (of course).

You do have a H-bridge, I guess.

I don't know wether sophisticated AC-TIGs do it this way, but I would try it this way. ... if I could not get my hands onto a TIG and connect a scope to it for an easy verification.*) Before you ask: No, I don't have one. Good AC-TIGs are to expensive for me. So I don't have a TIG at all. But if your modifcation works, I'll have to rethink that.

Nick

...I liked the site I found where a German engineer had modified a washing machine into a beer brewing machine....

Steve

That one?

Nick from Munich/Bavaria