Help me explain a conundrum (new TIG inverter)

[Ignoramus20351]

I made a new inverter bridge (as you remember, I fried the old one).

This time I made it from 400 A Eupec IGBTs, which obviated the need
for paralleling and made everything more compact.

It works on a bench. I use a homemade inductor in the DC line made of
about 300 ft of 12 ga cable from Home Depot. Here's a conundrum: the
DC-DC voltage behaves differently depending on the load: a direct
short vs. a wirewound 0.4 ohm resistor.

All pictures including oscilloscope screenshots, are here:

http://igor.chudov.com/projects/Homemade-TIG-DC-to-AC-Inverter/07-New-Bridge/

Any explanation? Any comparison of the welding load (coiled 40 ft
ground and 25 ft TIG torch welding cables, welding arc etc) with
this wirewound resistor?

i

 

[Pooh Bear]

I made a new inverter bridge (as you remember, I fried the old one).

This time I made it from 400 A Eupec IGBTs, which obviated the need
for paralleling and made everything more compact.

It works on a bench. I use a homemade inductor in the DC line made of
about 300 ft of 12 ga cable from Home Depot. Here's a conundrum: the
DC-DC voltage behaves differently depending on the load: a direct
short vs. a wirewound 0.4 ohm resistor.

All pictures including oscilloscope screenshots, are here:

http://igor.chudov.com/projects/Homemade-TIG-DC-to-AC-Inverter/07-New-Bridge/

Any explanation? Any comparison of the welding load (coiled 40 ft
ground and 25 ft TIG torch welding cables, welding arc etc) with
this wirewound resistor?

Load inductance ?

Graham

 

[Ignoramus20351]

Load inductance ?

Graham, I tend to agree with you. Yes, about the only thing that could
matter is indeed load inductance. I also suspected the same (see my
webpage), and I am glad that you place your more informed opinion in
the same direction as my poorly informed guess.

The questions in my mind is, just what exactly happens in the circuit
so that load inductance plays the role that it does, and how would
this possibly translate to welding.

Thanks a lot!

i

 

[Boris Mohar]

I made a new inverter bridge (as you remember, I fried the old one).

This time I made it from 400 A Eupec IGBTs, which obviated the need
for paralleling and made everything more compact.

It works on a bench. I use a homemade inductor in the DC line made of
about 300 ft of 12 ga cable from Home Depot. Here's a conundrum: the
DC-DC voltage behaves differently depending on the load: a direct
short vs. a wirewound 0.4 ohm resistor.

All pictures including oscilloscope screenshots, are here:

http://igor.chudov.com/projects/Homemade-TIG-DC-to-AC-Inverter/07-New-Bridge/

Any explanation? Any comparison of the welding load (coiled 40 ft
ground and 25 ft TIG torch welding cables, welding arc etc) with
this wirewound resistor?

Maybe I missed it but I guarantee you that you will get far more help once
you post the schematics somewhere. It is hard to discern from the picture
but it looks like oscillation along with ringing. Oscillation can be a
killer.

 

[Ignoramus6826]

Here's the schematic that I want to have:

http://igor.chudov.com/projects/Homemade-TIG-DC-to-AC-Inverter/09-Snubber/

It is similar to what was used for original question, except that I
did not then have the diodes on the left.

i

Maybe I missed it but I guarantee you that you will get far more help once
you post the schematics somewhere. It is hard to discern from the picture
but it looks like oscillation along with ringing. Oscillation can be a
killer.

--

 

[The Phantom]

Here's the schematic that I want to have:

http://igor.chudov.com/projects/Homemade-TIG-DC-to-AC-Inverter/09-Snubber/

It is similar to what was used for original question, except that I
did not then have the diodes on the left.

i

Where's the inductor made of the roll of 12Ga wire?