SUCCESS! TIG DC --> Advanced SquareWave INVERTER is working (prototype)

[Ignoramus28489]

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

Here you see my first working prototype of the IGBT based TIG
inverter. Again, this is an add on inverter for making Advanced Square
Wave AC from DC supplied by the welding machine.

Some highlights (see schematic page for component info:

I used Semikron SKHI 23/12 boards for driving the gates

I used four Toshiba 200A IGBTs, each of them is a half bridge,
so I have two paralleled full bridges with 400 A capacity.

A regulated current limited DC power supply was used for
testing

No snubber circuit yet

On the oscilloscope you see:

top -- voltage across the AC rail. You see some nice
ripple caused by the lack of snubber circuitry.

bottom -- voltage at the gate of one of the half bridges

My plans include building a robust snubber circuit (I already
have all components for a RC snubber), as well as fabricating a
sensible enclosure that would fit inside my welder.

As I intended, no deadtime is seen here (the bridge conducts
all the time, there are no transient "dead" intervals but there are
transient shorts).

I feel that this is a nice milestone in my project. I feel that I
have, in principle, proven that I can get to the completion of the
project. All I now need is not to **** anything up. To that effect, I
should make a nice snubber circuit and err on the side of overbuilding
that snubber. I should manufactore an enclosure that provides proper
mounting, vibration protection and cooling. After that, I should make
sure that front panel controls are properly installed and are
protected from EMI.

i

 

[Ignoramus28489]

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

oops, make it

http://igor.chudov.com/projects/Homemade-TIG-DC-to-AC-Inverter/01-Prototype-1/

i

 

[Christopher Tidy]

oops, make it

http://igor.chudov.com/projects/Homemade-TIG-DC-to-AC-Inverter/01-Prototype-1/

i

And someone said this guy was a troll? Well done Iggy - it looks great!

Chris

 

[Ignoramus28489]

And someone said this guy was a troll? Well done Iggy - it looks great!

Thanks... It is rare, I suppose, that people would assemble inverter
circuits for the purposes of trolling...

i

 

[Christopher Tidy]

Thanks... It is rare, I suppose, that people would assemble inverter
circuits for the purposes of trolling...

i

I think that would be limited to academic trolls on $100k research
budgets. Now there's a thought. Perhaps Cliff is a sociology postgrad
conducting some kind of experiment . You never know...a guy got a
grant to pursue art through shoplifting in England recently!

Chris

 

[Jon Elson]

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

Here you see my first working prototype of the IGBT based TIG
inverter. Again, this is an add on inverter for making Advanced Square
Wave AC from DC supplied by the welding machine.

Well, this is sure progress. But, you haven't run actual
welding currents through this yet, I gather. When the currents
in the IGBTs reach even 50% of rating, that's when all the
effects of the wiring layout are going to start showing up.
Since this is inherently a current-limited application with
the TIG power source, you do have the benefit that momentary
shorting of the welder should not cause massive shoot-through
currents.

Good luck taking it to the next step!

Jon

 

[Ignoramus28489]

Well, this is sure progress.

Yes. Thanks. There is progress.

It was conducting too much due to slow turnoff (due to my selection of
100 ohm turnoff resistors).

I experimented and essentially removed turnoff resistors (added
alligator clips across them).

After that, I just measured its cross conduction due to transient
shorts.

OCV Current

20V 0.035A
30V 0.047A
38V 0.050A

Would you think that it is sensible?

But, you haven't run actual welding currents through this yet, I
gather. When the currents in the IGBTs reach even 50% of rating,
that's when all the effects of the wiring layout are going to start
showing up. Since this is inherently a current-limited application
with the TIG power source, you do have the benefit that momentary
shorting of the welder should not cause massive shoot-through
currents.

Yep. That's why I hope to have some cross conduction and transient
shorts. Ideally (but not in reality) that would fully obviate the need
for a snubber circuit.

Since in reality all kinds of things can go wrong, I will have the
mother of all snubber circuits: a RC snubber between the main DC
rails, with extra 150V varistors, plus a little cap across every IGBT
witha 390V varistor. Just to cover my ass.

Good luck taking it to the next step!

Thanks... And thanks for support and actual helpful suggestions.

I find electronic design to be somewhat akin to computer programming,
I go through a succession of prototypes, there are subsystems, same
logic is used in debuggig problems etc.

i

 

[Gunner Asch]

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

Here you see my first working prototype of the IGBT based TIG
inverter. Again, this is an add on inverter for making Advanced Square
Wave AC from DC supplied by the welding machine.

Some highlights (see schematic page for component info:

I used Semikron SKHI 23/12 boards for driving the gates

I used four Toshiba 200A IGBTs, each of them is a half bridge,
so I have two paralleled full bridges with 400 A capacity.

A regulated current limited DC power supply was used for
testing

No snubber circuit yet

On the oscilloscope you see:

top -- voltage across the AC rail. You see some nice
ripple caused by the lack of snubber circuitry.

bottom -- voltage at the gate of one of the half bridges

My plans include building a robust snubber circuit (I already
have all components for a RC snubber), as well as fabricating a
sensible enclosure that would fit inside my welder.

As I intended, no deadtime is seen here (the bridge conducts
all the time, there are no transient "dead" intervals but there are
transient shorts).

I feel that this is a nice milestone in my project. I feel that I
have, in principle, proven that I can get to the completion of the
project. All I now need is not to **** anything up. To that effect, I
should make a nice snubber circuit and err on the side of overbuilding
that snubber. I should manufactore an enclosure that provides proper
mounting, vibration protection and cooling. After that, I should make
sure that front panel controls are properly installed and are
protected from EMI.

i

Dont forget to make your enclosure explosion proof.
Might I suggest a fly off top panel?

<G>

Gunner

"Pax Americana is a philosophy. Hardly an empire.
Making sure other people play nice and dont kill each other (and us)
off in job lots is hardly empire building, particularly when you give
them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you
for torturing the cat." Gunner

 

[[email protected]]

oops, make it

http://igor.chudov.com/projects/Homemade-TIG-DC-to-AC-Inverter/01-Prototype-1/

i

Is that a bullet lying on your bench near the center of this photo?
http://igor.chudov.com/projects/Homemade-TIG-DC-to-AC-Inverter/01-Prototype-1/dscf0002.jpg

I'm trying to figure out how that is involved in the development
process.

Dave
www.davewilson.cc

 

[Ignoramus14135]

Is that a bullet lying on your bench near the center of this photo?

No, it is a cartridge.

I'm trying to figure out how that is involved in the development
process.

I am sorry, I would have cleaned up better.

i

 

[Spehro Pefhany]

Is that a bullet lying on your bench near the center of this photo?
http://igor.chudov.com/projects/Homemade-TIG-DC-to-AC-Inverter/01-Prototype-1/dscf0002.jpg

I'm trying to figure out how that is involved in the development
process.

Dave
www.davewilson.cc

Could be a safety hazard if it accidentally got some juice flowing
through it. I'm impressively messy at times, but when stuff gets
powered up, it usually is very, very neat (especially expensive and/or
power stuff). Igor has the bulk of it relatively neatly placed on the
wood board, but there is enough clutter to be worrisome.


Best regards,
Spehro Pefhany

 

[Ignoramus14135]

Could be a safety hazard if it accidentally got some juice flowing
through it. I'm impressively messy at times, but when stuff gets
powered up, it usually is very, very neat (especially expensive and/or
power stuff). Igor has the bulk of it relatively neatly placed on the
wood board, but there is enough clutter to be worrisome.

Well, nowhere I have over 0.5 A flowing right now.

Anyway, regarding layout and such. The wooden board is used
temporarily so that stuff does not fall off the desk.

You may see 4" or so tall brass headers on top of the heatsink.

I am planning to mount a aluminum or steel flat piece on these
headers, attach a fiberglass insulation board on top, and mount
the driver circuit on that fiberglass board. The twisted wires leading
to IGBTs will be going to the sides of the flat piece and then into
the driver circuit. I will shorten then as well as I can.

All that I will enclose into some enclosure so that if the IGBTs blow
up, at least the rest of the welder will stay intact. I will also make
sure that this thing is cooled with two fans, one intake fan and one
exhaust fan.

My design approach is to go through a series of successive prototypes,
not to make a perfectly complete piece right away. I use the rsame
technique in my computer programming. It really works because mistakes
are caught early on.

Hence you see wooden boards, possibly alligator clips etc.

My mom gave me an earful last night. 20-25 years ago she worked at a
Soviet research center that was figuring out stolen (by spies and
such) US technology and how to use it in industry or defense.

So, she told me that it is a dangerous project for an amateur and that
attention to safety sohould go beyond merely reasonable levels. I
think that she is right. I would rather overbuild where enclosures and
such are concerned.

Some of safety highlights will be:

1. A solid enclosure that would stop flying molten IGBTs
2. A snubber circuit that is overbuilt, featuring big caps, big
resistors and big paralleled varistors.
3. Tiny snubbers on every IGBT
4. Normally closed temperature controlled switch to turn the circuit off
if temperature of the heatsink goes above 70 degrees C (about 158 F)

My Semikron 23 driver boards also feature IGBT overload protection,
they measure collector/emitter voltage and softly shut down the IGBT
if they sense an overload. The normal C/E voltage is about 2.5 or so
volts for 1,200 V IGBTs.

i

 

[Gunner Asch]

Is that a bullet lying on your bench near the center of this photo?
http://igor.chudov.com/projects/Homemade-TIG-DC-to-AC-Inverter/01-Prototype-1/dscf0002.jpg

I'm trying to figure out how that is involved in the development
process.

Dave
www.davewilson.cc

7.62x54R actually. Its a known length..so it makes a good reference
item, though its usually laid horizontally in the frame to make
comparison measurements easier.

The round also looks like a 30-40 Krag, or 6.5 Dutch, because of
foreshortening effect, but based on Iggies proclivities..Id have to
say the Russian round is more likely, and given the red primer
sealent..most likely East German..though it could be Slovak. I couldnt
blow up the photo large enough to read the head stamp code and tell
you which factory it came from



Gunner

"Pax Americana is a philosophy. Hardly an empire.
Making sure other people play nice and dont kill each other (and us)
off in job lots is hardly empire building, particularly when you give
them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you
for torturing the cat." Gunner

 

[ehsjr]

Is that a bullet lying on your bench near the center of this photo?
http://igor.chudov.com/projects/Homemade-TIG-DC-to-AC-Inverter/01-Prototype-1/dscf0002.jpg

I'm trying to figure out how that is involved in the development
process.

It's used for troubleshooting.
Ed

 

[Ignoramus14135]

7.62x54R actually. Its a known length..so it makes a good reference
item, though its usually laid horizontally in the frame to make
comparison measurements easier.

correct, it is 7.62x54. These rounds (50 year old surplus) are kind of
shitty, often do not fire. They are good for punching holes in
railroad tie plates though.

i

The round also looks like a 30-40 Krag, or 6.5 Dutch, because of
foreshortening effect, but based on Iggies proclivities..Id have to
say the Russian round is more likely, and given the red primer
sealent..most likely East German..though it could be Slovak. I couldnt
blow up the photo large enough to read the head stamp code and tell
you which factory it came from



Gunner

"Pax Americana is a philosophy. Hardly an empire.
Making sure other people play nice and dont kill each other (and us)
off in job lots is hardly empire building, particularly when you give
them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you
for torturing the cat." Gunner

--

 

[DoN. Nichols]

[ ... ]

[ ... ]

Well, nowhere I have over 0.5 A flowing right now.

Looking at the image zoomed in, it *appears* that the primer is
indented, so it may be an expended one with a replacement bullet seated
in it to serve as a setup gauge for reloading dies.

Still not sure why it is there, however.

Enjoy,
DoN.

 

[Jim L.]

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

Here you see my first working prototype of the IGBT based TIG

snip--Somehow I came across an IR2183(4) half bridge driver. Did you mention
that chip in one of your posts, or consider same? Jim

 

[Ignoramus1487]

snip--Somehow I came across an IR2183(4) half bridge driver. Did you mention
that chip in one of your posts, or consider same? Jim

I did indeed mention it. In fact I got two IR22141SS chips for free as
samples from IRF. But I did not use them.

I ended up using Semikron 23 boards, two boards, one for every half
bridge. They are quite straightforward to use and feel sturdier and
with more features.

i

 

[Winfield Hill]

Ignoramus1487 wrote...

I did indeed mention it. In fact I got two IR22141SS chips for
free as samples from IRF. But I did not use them.

I ended up using Semikron 23 boards, two boards, one for every
half bridge. They are quite straightforward to use and feel
sturdier and with more features.

One of my objections to the IR chips, if I have one, is their
rather slow delay times, e.g. about 200ns for the IR2183, IR2184
and 440ns for the IR22141, etc. And their rather long deadtime,
e.g. 400ns min for the programmable IR21834 driver. While such
long delay times may not affect your IGBT application, I've found
considerable benefit from having more flexibility and being able to
tightly control the driver's deadtime, even down to the 50ns level.
Furthermore, it's valuable to have tight control over the deadtime
as a function of load current, as offered by some TI Unitrode chips.

I've forgotten, how do Semikron 23 boards stack up in this regard?

 

[Ignoramus22022]

Ignoramus1487 wrote...

One of my objections to the IR chips, if I have one, is their
rather slow delay times, e.g. about 200ns for the IR2183, IR2184
and 440ns for the IR22141, etc. And their rather long deadtime,
e.g. 400ns min for the programmable IR21834 driver. While such
long delay times may not affect your IGBT application, I've found
considerable benefit from having more flexibility and being able to
tightly control the driver's deadtime, even down to the 50ns level.
Furthermore, it's valuable to have tight control over the deadtime
as a function of load current, as offered by some TI Unitrode chips.

I've forgotten, how do Semikron 23 boards stack up in this regard?

I can set deadtime by using two methods.

1. No interlock (bridged certain pair of contacts). I could use
turn-on and turn-off resistors for every gate. The more resistance,
the slower is the turn on or turn off. Turn on and turn off start
occurring simultaneously.

2. Interlock. That's the mode with guaranteed deadtime. I can set
deadtime by putting a resistor in the interlock contacts (same
contacts as in 1). Set from 0.9 to 10 uS. I suspect that I could go
lower as well.

As I said, I do not want deadtime. I want the bridge to short. So
I used method 1 and gate resistors.

I fucked it up in the sense that while the bridge does short and never
opens, the short time is too much. That makes for too much current
losses. I will need to go back and adjust the turn off resistors, I
think that I will set them to perhaps 47 ohm instead of the present
100 ohm.

I will make a separate post about it to s.e.d.

i