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.

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.

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

I see. Glad that we agree then.

Absolutely. I think (being a newbie to welding etc) that at 50-50 cycle, the amount od reverse polarity is excessive and leads to overheating of tungsten electrodes, without any benefit. So it is good to set cleaning (epecrode positive) to less than 50% of cycle.

That's right.

I bought my welding machine for $9.99 on ebay:

I also have pulsing. My welder is actually quite fancy, except for not having AC. All digital, etc.

That's the one ! Cheers.

Steve