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An update on my TIG inverter project

Hello Jon and Ignor,

To stop the HF arc starter "frying" electrically delicate parts of the welder, I have seen ordinary capacitors connected across the welders terminals to ground. (metal cabinet) O.1uF 400V. I use three caps just to make sure. Each terminal to ground and one across the output terminals of the welding power source. That is just extra insurance for me to feel better. The heavy input terminals of the arc starter unit will have RF bypass capacitors fitted.

Welding power source------> HF Arc starter ------> Tig Handpiece

This is the usual setup. Why would you rather not do that?

Bill H mentioned he fitted capacitors across all his rectifier blocks. This is normal practise. You can do the same to protect your IGBTs. A resistor and capacitor in series called a snubber circuit can be used to protect your semiconductors against transient voltage spikes.

Nice to see a hobbyist / enthusiast having a go at this project. I take my hat off to you.

Regards, John Crighton Sydney

Reply to
John Crighton
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Makes sense.

That's exactly what I will do. I will make my inverter circuit a part of the welder and place ot before the HF arc start circuit.

I actually did open up my welder's cabinet and looked inside.

It has two positions, DCEN and DCEP, on the switch that commutates lines.

If the DCEN/DCEP switch handle is in the intermediate position, there is no contact in the switch.

I could place my inverter between the 4 terminals (2 inputs and 2 outputs), and turn it on when the switch handle is in the intermediate position. Then the circuit would be switched electronically.

After that commutator switch, there is an arc start circuit.

That's great.Would you have some suggestions regarding capacitance of the cap and resistance of the resistor?

200 a power source, 30-1000 (or so) Hz switching speed, etc. 1,200 volts rating of IGBTs.

Thanks John, it is an interesting project indeed, I would love to get it to completion. As I said earlier, I already have IGBTs.

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Reply to
Ignoramus26315

Hello Ignor, sorry mate, I am out of my depth with that question but I did some googling for you and for my own interest. Resistors can be 10 ohm to 0.7 non inductive (not wire wound) Up to a few watts. Capacitors from 2.2 nF to 47nF Those values I just mentioned to you came from here

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I googled snubber design. If you read that thesis you might get some ideas how the combinations work.

I am reading your post in the welding group. The fellows in sci.electronics.design which I see you have cross posted too (good idea) will point you in the right direction as regards snubber design.

Get hold of some schematics of inverter welders and see what other welders use in that area. Check out the Lincoln and Miller web sites for their manuals. Look up the schematics. No harm in a hobbyist copying as a starting point.

Regards, John Crighton Sydney

Reply to
John Crighton

It seems to me that I recall a problem with snubbers. They not only have to withstand a certain level of average power, they also have to take a sharp, short power spike. Some types of resistors will exhibit non-passive failure. You need to use a resistor tolerant of spikes. Carbon composition resistors will be much more forgiving than metal film resistors. If you ask which kind they carry at Radio Shack, they will ask you to wait a moment while they check with the boss to see if they carry "resistors" (no help there).

Steve

Reply to
Steve Smith

Mouser.com is a good site - Vishay resistors come in all sorts of wattages and precisions....

Much wider than was provided below - but then I'm a stockholder and know them better. Dale - remember them - owned by Vishay.....

Martin Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder

John Cright> >

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Reply to
Martin H. Eastburn

John, thanks a lot. Idownloaded that thesis and will review it soon.

i
Reply to
Ignoramus14838

That has been my experience with Radio Shack as well. They know how to sell cell phones and toys, but would not know anything else.

i
Reply to
Ignoramus14838

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