Measured INDUCTANCE of my welding reactor

[Ignoramus21002]

I may have some more comments, but since this discussion has veered away
from just the inductor, why don't you start a new thread?

Well, I think that high inductance of the rreactor is kind of the
central point of IGBT circuit protection issues. I do not mind
starting a new thread, as such, but I also think that this thread is
quite good.

Feel free to start a new thread, I will be happy to hear your
thoughts.

i

 

[The Phantom]

Well, I think that high inductance of the rreactor is kind of the
central point of IGBT circuit protection issues. I do not mind
starting a new thread, as such, but I also think that this thread is
quite good.

Feel free to start a new thread, I will be happy to hear your
thoughts.

i

I started a new thread, with some questions for you.

 

[Ignoramus21002]

I started a new thread, with some questions for you.

Great! I answered them.

i
--

 

[Glen Walpert]

No, Toshiba MG200Q2YS40.

See
http://igor.chudov.com/projects/Hom...er/Schematic/Toshiba-MG200Q2YS40_DAT-IGBT.pdf

A quick check failed to turn up any Toshiba spice models.

Yes, more than once.

I listed a few reference papers on my webpage

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


That's right. The design is really quite simple. I have no plans to do
such pulse shaping, that opens big trouble.

Actually pulse shaping avoids big trouble, but you can't do it with
your supply.

Here are some of my thoughts on this. Feel free to shoot them down.

1. During regular welding operation, switching of the H bridge would
happen relatively quickly and I hope that it would happen within one
microsecond. Furthermore, it is possible that I could make the bridge
short for a fraction of a uS, rather than be open for a uS.

Such very small duration shorts or opens can be taken care of with a
relatively small capacitor. If a duration of the open condition is
within 2 uS, I calculated that a capacitor to absorb the current for
the duration needs to be quite small and affordable.

Right, a very small overlao is best.

2. Complete turn offs of the bridge should NOT happen during
welding, on a _regular_basis. I cannot be running a bead and turning
the welder's commutator handle at the same time.

Possible situations when a turn off would happen are:

1) failure of the drive circuit
2) failure of the power supply
3) some other failure
4) someone maliciously trying to turn off the circuit

In any case, these are rare events. I think that I can have a snubber
circuit like a RCD, and also a bunch of transorbs (varistors). I
already bought some varistors. That ought to take care of such rare
events.

Could work.

3. I hope that arc that extinguishes, such as when I withdraw the
welding torch, is not going to generate voltage spikes and dI/dt of
similarly high magnitude, as it would happen more slowly. Is that
correct?

Yes, as the arc is lengthened the voltage will go up and current will
gradually drop to near zero before the arc extinguishes.

 

[Ignoramus6607]

A quick check failed to turn up any Toshiba spice models.

That's unfortunate...

Actually pulse shaping avoids big trouble, but you can't do it with
your supply.
Yep...



Right, a very small overlao is best.

I will try very hard to do it.

Could work.

Glen, would you suggest any sensible values for the cap and resistor? I
have some high power diodes lying around (150 A, IIRC. I could
parallel 3 of them).

Yes, as the arc is lengthened the voltage will go up and current will
gradually drop to near zero before the arc extinguishes.

That's very nice to know. Thanks a lot. Thoughts on sensible snubber
component values would be appreciated greatly.

i

 

[Glen Walpert]

Glen, would you suggest any sensible values for the cap and resistor? I
have some high power diodes lying around (150 A, IIRC. I could
parallel 3 of them).

Sensible snubber component values need to be carefully calculated
based on a more complete circuit model than I have time for - one
which includes R, L and C on both sides of the H-Bridge. (The welding
leads will have significant inductance also.) All of those things Win
said you need to know to verify a good spice model also need to be
known for a good pencil and paper design analysis. I will do both
pencil and paper analysis and a Spice model when/if I ever get around
do building a TIG welder - it is easy to make errors with either one,
possible but less likely to make the same error with both. Agreement
of analysis, simulation and hardware test is what I look for in a new
design.

Since you do not appear to be prepared to do a thourough design
analysis either, designing per the snubber application note you
previously mentioned, ramping up your supply current slowly and
monitoring your snubber performance would appear to be your other
option.

The high power diodes you have hanging around may not be the most
suitable. "Soft Recovery" diodes as recommended in the IR Application
Notes would be better and are probably not too expensive.

 

[Ignoramus26744]

Sensible snubber component values need to be carefully calculated
based on a more complete circuit model than I have time for - one
which includes R, L and C on both sides of the H-Bridge. (The welding
leads will have significant inductance also.) All of those things Win
said you need to know to verify a good spice model also need to be
known for a good pencil and paper design analysis. I will do both
pencil and paper analysis and a Spice model when/if I ever get around
do building a TIG welder - it is easy to make errors with either one,
possible but less likely to make the same error with both. Agreement
of analysis, simulation and hardware test is what I look for in a new
design.

That's very sensible.

Since you do not appear to be prepared to do a thourough design
analysis either, designing per the snubber application note you
previously mentioned, ramping up your supply current slowly and
monitoring your snubber performance would appear to be your other
option.

Yes, I think that it is the safest approach.

The high power diodes you have hanging around may not be the most
suitable. "Soft Recovery" diodes as recommended in the IR Application
Notes would be better and are probably not too expensive.

I see. Are you referring to AN-1048, tig welder design?

i