Driver for IGBT? (-ve off and +ve on from CMOS)

You're going to have to select the Rce, Cce or the IGBTs, and thoroughly study the operating range of the power elements. It is far more involved than simply plugging values into their app circuit and reading "typical" graphs. If the damned drive is that expensive then go to a GMR and actually quantify the current with complete isolation and more than sufficient accuracy and bandwidth.

Thanks, I have a very old Cyber Tig. It is pictured here:

I just went out to weld a little bit (with stick) and looked at current. You are right, it fluctuates a great deal around the setting.

I do, in fact, have manuals for it, with a few missing pages here and there.

Whew, the "reactor" is larger and heavier than the transformer! That should also make a hell of a lot of high-energy RFI and serious high dV/dt spiking as the arc is under way. Creaming Ignoramus1797's delicate IGBT power-control electronics. :>(

I don't know about that reactor, but its size shows that it'll store a considerable amount of energy. And I have experienced massive blown-out electronics (vaporized traces, bad ICs, etc.), whose only sin was to be grounded, via the ac power cord, to a large telescope frame that had something arc welded to it on the other side of the frame during the night shift. Arc welder RFI currents are powerful, and will flow wherever they can!

And you have to make sure that short doesn't ever (even once, during testing) persist for too long...

Best regards, Spehro Pefhany

If your manual is incomplete then go to the link I provided and get a complete manual (free) which will include the schematic and volt-ampere curves. I would have taken a look but I can't read the third digit in the serial number on your nameplate photo.

Just because your unit is rated at 200 A does not mean it will not put out well over that into a short, and just because it is rated at 70 V open circuit does not mean that the "inductive kick" of that big "reactor" will not push the voltage well over 1200 V when your IGBT attempts to turn off (probably with a big bang, one time only) - you had better provide someplace for that "reactor" energy to go when the IGBTs turn off, if you want them to turn off more than once!

Also note that the volt-ampere curves refer to the RMS value of DC current, because there is a fair bit of ripple, with peak currents higher than RMS value.

My model is old, so I called Hobart. They were confused, since my spec number applied to a Cyber Tig 150, and yet my Cyber Tig is clearly a

Someone will hopefully call me back and email the manual, if available.

You are 100% right. I realized that last night, when I looked at the amp gauge while welding and intentionally creating shorts.

That means, pretty much, that I have to parallel my 200A IGBTs. I am glad that I have 4 of them.

As far as protection from overvoltage, I plan to implement a snubber circuit.

Yes, that's true.

I appreciate your insightful comment.

Hi Winfield, I am very interested to know what you know about that reactor, its inductance etc. Thanks a lot.

Oh, I see. That's separate from the mere inductance issue, is that right? I am going to find some info on whatever it is.

By the way, I uploaded the manuals for my welder (although, surprisingly, the manual is for a Cyber Tig 150, but they insist that it is my "spec number".

That's why he must make sure his bridge shorts rather than opens during switching.

robert

That probably won't help much, the EMP comes from the arc, and its dI/dt variations blast right back into the welder's circuits, creating high-frequency V = L dI/dt spikes, where L is your big rqeactor, plus lots of other wiring inductance, etc.

I don't have a TIG welder, but if I (hopefully) ever have a good enough excuse to buy one, it'll be a Hobart.

I simply love companies that publish manuals on the Net. It's also a great service not only to the unfortunate owner who lost his manual, but also to the would-be customer who can see exactly what he's gonna get.

That said -- your Ignoramus's welder looks like a massive EMP device. No electronics is going to survive this thing.

robert

Hobart and Miller manuals are available from millerwelds.com. Actually, it seems that it is Miller that distributes Hobart manuals. Hobart and its rights were bought in some complicated business transactions.

I uploaded manuals for my cybertig to

What if the bridge shorts instead of opens during th switching event? Would that help?

Indeed. And he won't find detailed instructions on doing that in any data sheet or app note I know of, since they all assume or explicitly show some reasonable approximation of a constant voltage supply and try to avoid "shoot-through". i is exploring uncharted territory here and I think he should at the very least get an oscilloscope so he can measure the on overlap time, start at the lowest possible current setting and wear safety glasses and a face shield at all times his equipment is energized. Buying a few dozen spare IGBTs and gate drivers would be a good idea too.

OTOH, I think i might want to reconsider his entire approach, especially if he wants to wind up with a really useful result. Polarity reversals on his CC supply will let him manual TIG weld aluminum in the event he can pull it off, but to duplicate the very useful "foreground/background" pulse capabilities of a good inverter welder he needs to go in and convert it to constant voltage by providing new SCR controls to let the existing 3-phase SCR bridge charge a new capacitor bank to an adjustable voltage (which would normally be set between 40 and 80 volts or so), which would feed his new IGBT bridge, which would drive the arc through the existing "filter reactor", which I am guessing is on the order of 10 uH but he should measure it since the manual provides no value for it. This of course means he needs to create a fairly complex PWM controller to make his IGBTs control current and might not obviate the need for the few dozen spares.

While figuring out how to do one or the other of these he could also probably learn to weld aluminum with DC :-).

I would base my selection on features rather than brand if I were ever to replace my ancient Miller Dialarc HF with a modern inverter, they all come with manuals. And while making electronics work reliable in a high EMI (ElectroMagnetic Interference) environment is not easy, it has been done many times, especially in military and medical gear. I sometimes do a crude EMI immunity test by wrapping a couple of turns of welding cable around the DUT (Device Under Test) and firing up a

Yes, see other posts. But it won't help with providing adequate EMI immunity for your gate drive circuits, something the Semikron driver design probably gave some consideration to.

I am confused. My plan for my inverter circuit is to place it BEFORE the high voltage, high frequency arc starter circuit. I believe, rightly or wrongly, that the HF unit is isolated from the power supply in the sense of conducting interference. If I am mistaken, or am thinking about a wrong issue, I will appreciate being corrected.

I have two oscilloscopes, Tek 475 and Tek 2465, IIRC. Both actually work. You see, I sell military surplus stuff on ebay and accumulated some equipment. I will probably sell Tek 2465 eventually, but Tek 475 is my workhorse for testing stuff.

That said... How do you get to plot rare events such as my switchings, on the oscilloscope, so that I see voltage spikes.

Also, would high voltage not endanger the oscilloscope itself?

I will actually conduct first tests with a small regulated DC power supply, current limited etc. Not even with the welder.

haha

Can you elaborate on these capabilities?

Are you talking about different absolute values of voltage in negative vs. positive cycle?

Or are you talking about pulsing output where current is varied through time, say changing every X seconds from high to low current?

If you are talking about the latter, then my tig welder supports pulsing, it has a few controls for it.

IOW, you are suggesting to place the inverter before the "reactor"?

I think that it's kind of a fun project. I am not incredibly worried about frying the electronics that I build, I mean, it is not that much money. I would be upset, sure, but it is not the end of the world.

What I would be more upset is if somehow, this switching cound damage the welder itself.

I think the design resistance for serial lines is about 300 ohms. at 40Khz that's equivalent to about 260nF what sort of capacitance do these IGBT gates have ?

Bye. Jasen