Repairing TIG welder: safety precautions

[Sapre]

I’ve had intermittent problems with my parweld 200 acdc tig welder.

I managed to do some test with a multimeter and oscilloscope. Im using a high voltage diff probe but i also want to connect the welder to an isolating transformer as a second safety measure..

Im thinking of a site isolating transformer (3kva) to be able to handle the max current even though likely most test wont be under load.

I would also prefer to use a 110v step down isolating transformer as a further measure (and since i have other uses for it), and was wondering if i could test the switching circuitry under this lower voltage? I dont see why not but thought to check…

Thanks for any thoughts/tips!

 

[hotponyshoes]

I'm not really sure how welders work but don't they just step the incoming voltage back up?

Ie a multi-voltage welder puts 300vdc on regardless of you plugging it into a 230v or 110v socket?

If you can find a service manual it should tell you how & were to test it safely

 

[eddie49]

Yes, the inverter power circuit will work ( or fail... ) on the 156v DC out of rectified-and-smoothed 110v AC instead of the normal 325v DC from straight 240 mains. However, I don't think a 150 volt DC shock is much less painful than a 325v one!

This thread describes the successful repair of a DC TIG inverter welder:

Thread 'Parweld XTT182DV no power'

Oct 27, 2021

I have an XTT182DV inverter set, which is currently not showing any signs of life.

A preliminary investigation is showing that I am getting AC voltage to the first pair of rectifiers and when the DC side of the rectifiers is disconnected from the main PCB there is 240V DC. When the DC side of the rectifiers is reconnected, the voltage is pulled down, possibly indicating a short circuit.

Since the DC voltage is getting pulled down, there is no voltage on the control side, therefore no power indication light or anything else. Nothing is tripping as the short circuit load is being...

• The_Motorcyclist
• Replies: 20
• forum: GYS, Parweld, Jasic

This thread covers another Parweld repair:

T

Thread 'Parweld XTM 201i "went bang"'

Feb 6, 2025

Hi everyone, apologies to bring problems as my first post but i'm in need of some more experienced folks than myself to help diagnose this.

So I have a Parweld XTM 201i, its been a great little machine and never had any problems with it, until a few weeks ago it went pop upon turning on the machine (no trigger pulled, just plugged in and turned on made it go)

Now, being that I have no warranty and am also somewhat electrically experienced, I had the cover off to find a group of 3 resisters completely obliterated. I have no schematic for this machine and parweld wont even reply to my...

• Tommy Tig
• Replies: 22
• forum: GYS, Parweld, Jasic

In Post #21 of that thread I refer to using a current-limited low voltage DC bench power supply to run the inverter power section, instead of the 325v DC that appears across the smoothing capacitors after the incoming AC mains is rectified. Doing this not only avoids using live AC mains, but also protects expensive replaced IGBTs from being destroyed by faulty gate drive signals.

The usual reason for running an inverter via a mains isolating transformer is to avoid potential conflicts with the earth clip of your 'scope probe. The answer could be to disconnect the mains earth of your oscilloscope ( !! ) , or to invest in a modern cordless plastic-cased scope.