Welder Tig AC/DC blown house fuses, shorted IGBT

[florkk]

Hello, i have strange problem, i have my welder about 3 years, its ac/dc tig , few days ago, when i weld in 160A ac range, tig blown house fuses, fuse was 10A, after third shut down time, when i go to turn on automatic fuse, welder try to starts, light all indicators, and after 1 sec blown fuse again. i was know that something broken inside. i open welder, and after few minutes of searching i sound two shorted igbt, in some kind of power supply board. in total the are 4 igbt, connected to 4 individual wires, going to strange looking transformer. The igbts are IKW50N60T. i bought 2 new for replace, replaced shorted one, and welder work again, i also replace home fuses from 10A to 16A with delay. i use welder for about 1h, and on my mistake when i was finishing weld, i touch tungsten to base metal( where i have connected ground lead) and it tungsten stick for 1s. house fuse blown again, and again when i turn it on, and turn on welder, it again blown fuses, so again it seems like shorted igbt, i open again welder, and again the same 2 igbt that i replace got short. right now i order again new set of IKW50N60T, but why its again blow, any ideas? its any way to protect igbs with some diode or something? igbt gate is controlled by transformer, and few resistor and diodes.

[florkk]

PS. IGBT after damage have all 3 legs shorted to each other, so G E C are shorted

[TheMG]

Sounds like there may be a deeper problem that is causing the IGBTs to fail.

Welder should be able to handle short-circuiting the output without any damage, it should current-limit. So I would suspect maybe there's some sort of issue in the control circuits responsible for limiting the output current, causing the IGBTs to operate beyond their maximum ratings and failing.

[florkk]

again i replace igbt and after 30min ac welding its short again, i check temperature of this two transisors and they were cold. they are k50t60 600v 80A , gate is controlled by one small transformer two diodes and few resistors. maybe someone know what can damage this igbt, i think its not heat, and its not over voltage and current. without scope i can measure anything? idk why but im still thinking about gate voltage, or something connected with gate

[MadTux]

Sure you got original IGBTs?
Chinese bastards especially like to fake power semiconductors (experienced that myself), since they get best margins there.

Apart from that, perhaps find a cheap high voltage differential probe (7A22 or 7A13 are probably the cheapest, if you get a Tek7000 mainframe) and see, wether the gate drive signal is good/the same on all 4 IGBTs. And perhaps find some real heatsinks for them, looks like the usual chinesium crap welder, with heatsinks made from whatever scrap there was available.

[transistor12]

Chinese bastards !

[tokenpete]

Here is a video to help you diagnose. You probably have a blown zener on the other side of the board. You need to use a 18V and 8.2V zenner in opposite polarity to protect the gate on the igbt.

[fenugrec]

+1 on checking gate protection diodes - possibly 2 zeners back to back. Find their voltage ratings and replace, they are cheap, not worth testing. If your IGBTs shorted G-E-C then some high voltages may have fed through the gate and damaged those diodes.

[FIXITNOW2003]

what make this welder @? may have circuit

[tokenpete]

There are many brands globaly using (used now obsolete) the same design sort of with minor changes, they come from NANTONG FREE ELECTROTECHNOLOGY

In the UK R-Tech welding had these, looking at the OP's images I think his is an Everlast TIG judging by the front panel feet

I have attached

1. The schematic for the power section
2. The schematic for the Main Control Board
3. The parts listing as referenced in the schematics
4. A generic manual for this series of machine

I have been fixing these machines for 20 years, they are like my babies