SUCCESS! TIG DC --> Advanced SquareWave INVERTER is working (prototype)

oops, make it

And someone said this guy was a troll? Well done Iggy - it looks great!

Chris

Thanks... It is rare, I suppose, that people would assemble inverter circuits for the purposes of trolling...

I think that would be limited to academic trolls on $100k research budgets. Now there's a thought. Perhaps Cliff is a sociology postgrad conducting some kind of experiment :-). You never know...a guy got a grant to pursue art through shoplifting in England recently!

Chris

Well, this is sure progress. But, you haven't run actual welding currents through this yet, I gather. When the currents in the IGBTs reach even 50% of rating, that's when all the effects of the wiring layout are going to start showing up. Since this is inherently a current-limited application with the TIG power source, you do have the benefit that momentary shorting of the welder should not cause massive shoot-through currents.

Good luck taking it to the next step!

Jon

Yes. Thanks. There is progress.

It was conducting too much due to slow turnoff (due to my selection of

I experimented and essentially removed turnoff resistors (added alligator clips across them).

After that, I just measured its cross conduction due to transient shorts.

OCV Current

Would you think that it is sensible?

Yep. That's why I hope to have some cross conduction and transient shorts. Ideally (but not in reality) that would fully obviate the need for a snubber circuit.

Since in reality all kinds of things can go wrong, I will have the mother of all snubber circuits: a RC snubber between the main DC rails, with extra 150V varistors, plus a little cap across every IGBT witha 390V varistor. Just to cover my ass.

Thanks... And thanks for support and actual helpful suggestions.

I find electronic design to be somewhat akin to computer programming, I go through a succession of prototypes, there are subsystems, same logic is used in debuggig problems etc.

Dont forget to make your enclosure explosion proof. Might I suggest a fly off top panel?

Gunner

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner

Is that a bullet lying on your bench near the center of this photo?

Dave

No, it is a cartridge. :)

I am sorry, I would have cleaned up better.

Could be a safety hazard if it accidentally got some juice flowing through it. I'm impressively messy at times, but when stuff gets powered up, it usually is very, very neat (especially expensive and/or power stuff). Igor has the bulk of it relatively neatly placed on the wood board, but there is enough clutter to be worrisome.

Best regards, Spehro Pefhany

Well, nowhere I have over 0.5 A flowing right now.

Anyway, regarding layout and such. The wooden board is used temporarily so that stuff does not fall off the desk.

You may see 4" or so tall brass headers on top of the heatsink.

I am planning to mount a aluminum or steel flat piece on these headers, attach a fiberglass insulation board on top, and mount the driver circuit on that fiberglass board. The twisted wires leading to IGBTs will be going to the sides of the flat piece and then into the driver circuit. I will shorten then as well as I can.

All that I will enclose into some enclosure so that if the IGBTs blow up, at least the rest of the welder will stay intact. I will also make sure that this thing is cooled with two fans, one intake fan and one exhaust fan.

My design approach is to go through a series of successive prototypes, not to make a perfectly complete piece right away. I use the rsame technique in my computer programming. It really works because mistakes are caught early on.

Hence you see wooden boards, possibly alligator clips etc.

My mom gave me an earful last night. 20-25 years ago she worked at a Soviet research center that was figuring out stolen (by spies and such) US technology and how to use it in industry or defense.

So, she told me that it is a dangerous project for an amateur and that attention to safety sohould go beyond merely reasonable levels. I think that she is right. I would rather overbuild where enclosures and such are concerned.

Some of safety highlights will be:

1. A solid enclosure that would stop flying molten IGBTs
2. A snubber circuit that is overbuilt, featuring big caps, big resistors and big paralleled varistors.
3. Tiny snubbers on every IGBT
4. Normally closed temperature controlled switch to turn the circuit off if temperature of the heatsink goes above 70 degrees C (about 158 F)

My Semikron 23 driver boards also feature IGBT overload protection, they measure collector/emitter voltage and softly shut down the IGBT if they sense an overload. The normal C/E voltage is about 2.5 or so volts for 1,200 V IGBTs.

The round also looks like a 30-40 Krag, or 6.5 Dutch, because of foreshortening effect, but based on Iggies proclivities..Id have to say the Russian round is more likely, and given the red primer sealent..most likely East German..though it could be Slovak. I couldnt blow up the photo large enough to read the head stamp code and tell you which factory it came from

Gunner

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner

It's used for troubleshooting. Ed

correct, it is 7.62x54. These rounds (50 year old surplus) are kind of shitty, often do not fire. They are good for punching holes in railroad tie plates though.

According to Ignoramus14135 :

Looking at the image zoomed in, it *appears* that the primer is indented, so it may be an expended one with a replacement bullet seated in it to serve as a setup gauge for reloading dies.

Still not sure why it is there, however. :-)

Enjoy, DoN.

snip--Somehow I came across an IR2183(4) half bridge driver. Did you mention that chip in one of your posts, or consider same? Jim

I did indeed mention it. In fact I got two IR22141SS chips for free as samples from IRF. But I did not use them.

I ended up using Semikron 23 boards, two boards, one for every half bridge. They are quite straightforward to use and feel sturdier and with more features.

One of my objections to the IR chips, if I have one, is their rather slow delay times, e.g. about 200ns for the IR2183, IR2184 and 440ns for the IR22141, etc. And their rather long deadtime, e.g. 400ns min for the programmable IR21834 driver. While such long delay times may not affect your IGBT application, I've found considerable benefit from having more flexibility and being able to tightly control the driver's deadtime, even down to the 50ns level. Furthermore, it's valuable to have tight control over the deadtime as a function of load current, as offered by some TI Unitrode chips.

I've forgotten, how do Semikron 23 boards stack up in this regard?

Don't forget diodes in series with gate resistors to separately control on and off delays. Like this popular scheme for rapid turnoff, to get "break before make."

. ---+----/\/\-----+--- gate . | | . '--|