On Sat, 26 Nov 2005 08:19:57 GMT, Ignoramus29530
wrote:


Just wanted to say that after slight snubber circuit modifications
(more below), I was able to test my bridge under full welding power of
199 amps.

http://igor.chudov.com/projects/Home...5-Prototype-3/

I also added a cooling fan to cool the main heatsink with IGBTs, as
well as a heatsink for the big ass diode in the snubber circuit. I
drilled a hole in that second heatsink and tapped it for 3/8-20 NF
thread, and screwed the diode in.

It is cold in my garage, perhaps 35F. Given that, and the fan action,
all parts of the bridge stayed cool, except for the main heatsink,
which became warm. Under full power, the IGBTs are expected to produce
approximately 1.2 kW of heat.

Snubber modifications: I added a little Christmas tree of 150 V rated
varistors (total of 5 now), as well as a small 0.33 uF capacitor
across the DC rail. I also remounted the snubber diode by drilling a
tapping a heatsink that I had, and screwing the diode in.

The test (among many tests at smaller amps) went on for a couple of
minutes, until the breakers blew. Like I said, nothing warmed up (I
checked caps, diode, and varistors).

Congratulations! Was that 199 A into a short or into an arc?

Congrat's. I'm wondering if you came across any schematics of commercial tig
inverters during your hunt? Or are they drawn as black boxes? Thanks, Jim.

"Ignoramus12834" wrote in message
...
On Sat, 26 Nov 2005 14:12:01 GMT, Glen Walpert
wrote:
On Sat, 26 Nov 2005 08:19:57 GMT, Ignoramus29530
wrote:


Just wanted to say that after slight snubber circuit modifications
(more below), I was able to test my bridge under full welding power of
199 amps.

http://igor.chudov.com/projects/Home...5-Prototype-3/

I also added a cooling fan to cool the main heatsink with IGBTs, as
well as a heatsink for the big ass diode in the snubber circuit. I
drilled a hole in that second heatsink and tapped it for 3/8-20 NF
thread, and screwed the diode in.

It is cold in my garage, perhaps 35F. Given that, and the fan action,
all parts of the bridge stayed cool, except for the main heatsink,
which became warm. Under full power, the IGBTs are expected to produce
approximately 1.2 kW of heat.

Snubber modifications: I added a little Christmas tree of 150 V rated
varistors (total of 5 now), as well as a small 0.33 uF capacitor
across the DC rail. I also remounted the snubber diode by drilling a
tapping a heatsink that I had, and screwing the diode in.

The test (among many tests at smaller amps) went on for a couple of
minutes, until the breakers blew. Like I said, nothing warmed up (I
checked caps, diode, and varistors).

Congratulations! Was that 199 A into a short or into an arc?

Thanks... It was into a short. To have a welding arc, I would need to
put the bridge to the proper place on the commutator.

i
--

I have just scanned the schematic for a Hitachi inverter TIG and added
it to the dropbox.
The jpg is about 1mb.

http://metalworking.com/DropBox/HitachiInvTIG.jpg
http://metalworking.com/DropBox/HitachiInvTIG.txt

Ignoramus12834 wrote:

On Sat, 26 Nov 2005 16:47:25 GMT, Jim L. wrote:

Congrat's.


Thanks. I may try to weld aluminum this weekend.

I'm wondering if you came across any schematics of commercial tig
inverters during your hunt? Or are they drawn as black boxes? Thanks, Jim.


I have not found anything.

The only thing that my inverter does not have, is control of power
when electrode is negative, and separate control when electrode is
positive (I think that it is called AC balance). For my inverter, the
absolute value of the voltageand current is the same for positive vs
negative half cycle.

Basically, I think, commercial inverters are a lot like mine, they
have a timing circuit, drive circuit, full bridge driven by FETs
(MOSFET or IGBT), a snubber (maybe) and controls.

I am just a chump who put together my first electronic contraption, so
I may not know as much as more learned members of these newsgroups.

Take my answer for what it is worth.

i

"Ignoramus12834" wrote in message
.. .

On Sat, 26 Nov 2005 14:12:01 GMT, Glen Walpert
wrote:

On Sat, 26 Nov 2005 08:19:57 GMT, Ignoramus29530
wrote:

Just wanted to say that after slight snubber circuit modifications
(more below), I was able to test my bridge under full welding power of
199 amps.

http://igor.chudov.com/projects/Home...5-Prototype-3/

I also added a cooling fan to cool the main heatsink with IGBTs, as
well as a heatsink for the big ass diode in the snubber circuit. I
drilled a hole in that second heatsink and tapped it for 3/8-20 NF
thread, and screwed the diode in.

It is cold in my garage, perhaps 35F. Given that, and the fan action,
all parts of the bridge stayed cool, except for the main heatsink,
which became warm. Under full power, the IGBTs are expected to produce
approximately 1.2 kW of heat.

Snubber modifications: I added a little Christmas tree of 150 V rated
varistors (total of 5 now), as well as a small 0.33 uF capacitor
across the DC rail. I also remounted the snubber diode by drilling a
tapping a heatsink that I had, and screwing the diode in.

The test (among many tests at smaller amps) went on for a couple of
minutes, until the breakers blew. Like I said, nothing warmed up (I
checked caps, diode, and varistors).

Congratulations! Was that 199 A into a short or into an arc?

Thanks... It was into a short. To have a welding arc, I would need to
put the bridge to the proper place on the commutator.

i

Ignoramus12834 wrote:

For my inverter, the absolute value of the voltageand current is the same
for positive vs negative half cycle.

What is wrong behind my idea to switch the bridge asymetric? For example
70% one direction, 30% the other. This way, you get a (averaged)
DC-offset.


Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO - YADRO - Eigenbau-Digitalanzeige

David Billington wrote:
I have just scanned the schematic for a Hitachi inverter TIG and added
it to the dropbox.
The jpg is about 1mb.

http://metalworking.com/DropBox/HitachiInvTIG.jpg
http://metalworking.com/DropBox/HitachiInvTIG.txt

This isn't much of a schematic. All the circuit boards
are just rectangles. Also, this is a DC only welder.

Jon

I thought it was worthwile posting it as it does show some of the
details of the power side, if not the control system. It was mentioned
earlier in the thread that no schematics had been found so it may be of
some use. The welder is definitely AC and DC, if the schematic can't do
that then I guess the manual is wrong, but it is entitled "power
transistor controlled, AC/DC TIG arc welding power source".

Jon Elson wrote:

David Billington wrote:

I have just scanned the schematic for a Hitachi inverter TIG and
added it to the dropbox.
The jpg is about 1mb.

http://metalworking.com/DropBox/HitachiInvTIG.jpg
http://metalworking.com/DropBox/HitachiInvTIG.txt

This isn't much of a schematic. All the circuit boards
are just rectangles. Also, this is a DC only welder.

Jon

On Sat, 26 Nov 2005 17:55:02 GMT, Ignoramus12834
wrote:

On Sat, 26 Nov 2005 16:47:25 GMT, Jim L. wrote:
Congrat's.

Thanks. I may try to weld aluminum this weekend.

I'm wondering if you came across any schematics of commercial tig
inverters during your hunt? Or are they drawn as black boxes? Thanks, Jim.

I have not found anything.

The only thing that my inverter does not have, is control of power
when electrode is negative, and separate control when electrode is
positive (I think that it is called AC balance). For my inverter, the
absolute value of the voltageand current is the same for positive vs
negative half cycle.

They control balance with duty cycle control, which you can also do.
Start with 50-50, or maybe 60% SP (electrode negative) and 40% RP
(electrode positive). Practice with that until you can make
consistently good welds. With only 200 amps max current you'll be
limited to fairly thin aluminum, maybe 1/4" max. I'd suggest
starting with 1/8" material. Don't blame the machine if you don't
achieve instant success. A lot of excellent aluminum TIG welding
is done with straight AC machines. When you can lay a stack of dimes
in aluminum, then you can start tweaking the dutycycle or AC balance
to optimize penetration with just enough RP cleaning to do the job.

I've followed this saga with some interest, will be interested in your
results. I've thought about doing something like that for years,
but have never been motivated to do it because I've been satisfied
with the results I get with straight AC.

This is what my Hitachi TIG does and allows you to adjust the cleaning
action in AC mode.

Nick Müller wrote:

Ignoramus12834 wrote:

For my inverter, the absolute value of the voltageand current is the same
for positive vs negative half cycle.


What is wrong behind my idea to switch the bridge asymetric? For example
70% one direction, 30% the other. This way, you get a (averaged)
DC-offset.


Nick

Ignoramus18456 wrote:

I can control the period of TIME when voltage is positive, or
negative, as percentage of the cycle.

That's what I meant.


I cannot make the CURRENT or VOLTAGE on positive or negative different.

That's clear. But if you average the current flow (better to say
polarity) and do not have a 50:50 cylce, you will have a DC-offset.
Imagine having a 100:0 cyle. It would give you DC with one polarity (of
course).

You do have a H-bridge, I guess.


I don't know wether sophisticated AC-TIGs do it this way, but I would
try it this way. ... if I could not get my hands onto a TIG and connect
a scope to it for an easy verification.*)
Before you ask: No, I don't have one. Good AC-TIGs are to expensive for
me. So I don't have a TIG at all. But if your modifcation works, I'll
have to rethink that.

*) Oh, you should find information about this subject in good
theory-oriented welding books. I guess, they also do have pulsing. So
you will have to hook a uC to your whashing-machine ... err ... TIG.
:-))


Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO - YADRO - Eigenbau-Digitalanzeige

Nick Müller wrote:
*) Oh, you should find information about this subject in good
theory-oriented welding books. I guess, they also do have pulsing. So
you will have to hook a uC to your whashing-machine ... err ... TIG.
:-))

....I liked the site I found where a German engineer had modified a
washing machine into a beer brewing machine....


Steve

Steve wrote:

...I liked the site I found where a German engineer had modified a
washing machine into a beer brewing machine....

That one?
http://www.wambier.de/

Didn't know about that, but looks like fun! Prost!

Nick from Munich/Bavaria
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO - YADRO - Eigenbau-Digitalanzeige

"Don Foreman" wrote in message
...
On Sat, 26 Nov 2005 17:55:02 GMT, Ignoramus12834
wrote:

On Sat, 26 Nov 2005 16:47:25 GMT, Jim L. wrote:
Congrat's.

Thanks. I may try to weld aluminum this weekend.

I'm wondering if you came across any schematics of commercial tig
inverters during your hunt? Or are they drawn as black boxes?
Thanks, Jim.

I have not found anything.

The only thing that my inverter does not have, is control of power
when electrode is negative, and separate control when electrode is
positive (I think that it is called AC balance). For my inverter,
the
absolute value of the voltageand current is the same for positive
vs
negative half cycle.

They control balance with duty cycle control, which you can also do.
Start with 50-50, or maybe 60% SP (electrode negative) and 40% RP
(electrode positive). Practice with that until you can make
consistently good welds. With only 200 amps max current you'll
be
limited to fairly thin aluminum, maybe 1/4" max. I'd suggest
starting with 1/8" material. Don't blame the machine if you don't
achieve instant success. A lot of excellent aluminum TIG
welding
is done with straight AC machines. When you can lay a stack of
dimes
in aluminum, then you can start tweaking the dutycycle or AC balance
to optimize penetration with just enough RP cleaning to do the job.


He may be thinking of an asymmetrical square wave unit...



I've followed this saga with some interest, will be interested in
your
results. I've thought about doing something like that for years,
but have never been motivated to do it because I've been satisfied
with the results I get with straight AC.

Nick Müller wrote:
Steve wrote:

...I liked the site I found where a German engineer had modified a
washing machine into a beer brewing machine....

That one?
http://www.wambier.de/


That's the one !
Cheers.

Steve

Ignoramus18456 wrote:

I can control the period of TIME when voltage is positive, or
negative, as percentage of the cycle.

That's what I meant.

I see. Glad that we agree then.

But this might also mean, that we are equaly ignorant. I'm not a
welding-pro.


Absolutely. I think (being a newbie to welding etc) that at 50-50
cycle, the amount od reverse polarity is excessive and leads to
overheating of tungsten electrodes, without any benefit. So it is good
to set cleaning (epecrode positive) to less than 50% of cycle.

I just had a look in my welding book (not that much about TIG power
sources in there). It says, that you get a diode (when welding Al, but
even with steel) due to the oxyde in the puddle. That is the reason for
having a DC offset (when welding with AC). It is there to compensate the
diode effect. The offset doesn't seem to be very high. From the diagram,
I guess about 30%.


I bought my welding machine for $9.99 on ebay:

I know, that's the reason for the "washing machine"


I also have pulsing.

Seems that pulsing is only used with DC. If you would use it with your
H-bridge, you should have to switch polarity in sync with the pulses.
Can you adjust the base current and the max current?


My welder is actually quite fancy, except for not
having AC. All digital, etc.

LOL! "Digital". You have thumb wheels with digits. But looking at the
wire nest in that machine, is is damned analog.


Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO - YADRO - Eigenbau-Digitalanzeige

David Billington wrote:
I thought it was worthwile posting it as it does show some of the
details of the power side, if not the control system. It was mentioned
earlier in the thread that no schematics had been found so it may be of
some use. The welder is definitely AC and DC, if the schematic can't do
that then I guess the manual is wrong, but it is entitled "power
transistor controlled, AC/DC TIG arc welding power source".
The schematic very clearly shows a bridge rectifier at the output,
and the output terminals are marked "+" and "-".

Jon

Ignoramus12834 wrote:
It is a AC/DC welder. Look at FETs T21 and T22, you can see that they
can be used to supply either +, or -, or +/- to the line labeled
+. Whereas line marked - is the center tapped point of the secondary.

OH, heck, you are absolutely right! I was viewing the thing in Mozilla,
which just gives me a peephole view of the file. Yes, T21 and T22
are between the bridge rectifier and the output terminals. (Dumb
labeling of those, they should be electrode and work, not + and -.)

in AC mode, I think, only one half of the secondary winding is
working. I may be wrong, I slept only 3-4 hours for the last 2 days
and am barely thinking, .
No, only one half of the bridge rectifier is working. Presumably
the work terminal is connected to the center tap, and the bridge
always produces a + and a - voltage referenced to that. The two
transistors select from the two polarities. Certainly a minimum
solution to the problem.

Jon

Ignoramus12834 wrote:
On Sat, 26 Nov 2005 17:36:47 -0800, xray wrote:

On Sun, 27 Nov 2005 00:57:12 GMT, Ignoramus12834
wrote:


It is a AC/DC welder. Look at FETs T21 and T22, you can see that they
can be used to supply either +, or -, or +/- to the line labeled
+. Whereas line marked - is the center tapped point of the secondary.

I agree, except they appear to be bipolars, not FETs.


Could be. I thought that bipolar transistors are also field effect
transistors, that's why I said so. I am an amateur.
Bipolar Junction Transistors come in NPN and PNP types, and do not use
the field effect. They use base current to modulate (and amplify)
collector current.

Field effect transistors use the electric field between the gate and
source to modulate the resistance in the channel. Gate voltage
essentially controls drain current through this method. Generally,
gate current is zero.

Insulated Gate Bipolar Transistors are a combination of the two.
They really are a bipolar junction transistor with a FET connected
between the collector and base. They give many of the advantages
of both types. With the FET, the voltage drop across the drain-source
increases linearly with current. (It is a resistance, after all.)
With the Bipolar and IGBT, the voltage drop is almost flat with
changes in current, usually around 1.5 V. Regular bipolar junction
power transistors require a base current about 1/10th of the collector
current. With 100 A transistors, that amounts to 10 amps the control
circuit needs to deliver to the base. Darlington transistors have
at least 10 x higher gain, but the voltage drop will be double, a major
disadvantage. The IGBT solves that problem. The gate current required
is zero, once the gate capacitance has been charged.

One other pro/con thing about IGBTs is that, like other bipolars, the
forward voltage drop goes DOWN as they get hot. This effectively
prevents thermal runaway with single devices. But, it makes it a lot
harder to balance current in paralleled devices, as the hottest one
will have the lowest voltage drop, and thus get all the current.
(By comparison, the resistance of FETs goes UP with temperature,
making thermal runaway possible. But, it makes paralleling devices
a breeze, as they will self-equalize their current.)

Jon

Thanks for the very nice explanation Jon!
I guess I have been a tech for too long .. I just can't get into staying
current unless it is directly related to the problem I am trying to fix
If Iggy keeps this up I may just have to dust off all the test equip on my
bench and start playing again LOL. It is true what they say about never
going to work in a field that is a hobby. It really takes the joy out of it
in 30 years or so. I just got back from driving about 500 miles .. the last
20 in a snowcat .. just to turn a pot a couple of turns. Appreciate y'all
bringing some fun into the mix
Glenn
"Jon Elson" wrote in message
...
Ignoramus12834 wrote:
On Sat, 26 Nov 2005 17:36:47 -0800, xray
wrote:

On Sun, 27 Nov 2005 00:57:12 GMT, Ignoramus12834
wrote:


It is a AC/DC welder. Look at FETs T21 and T22, you can see that they
can be used to supply either +, or -, or +/- to the line labeled
+. Whereas line marked - is the center tapped point of the secondary.

I agree, except they appear to be bipolars, not FETs.


Could be. I thought that bipolar transistors are also field effect
transistors, that's why I said so. I am an amateur.
Bipolar Junction Transistors come in NPN and PNP types, and do not use
the field effect. They use base current to modulate (and amplify)
collector current.

Field effect transistors use the electric field between the gate and
source to modulate the resistance in the channel. Gate voltage
essentially controls drain current through this method. Generally,
gate current is zero.

Insulated Gate Bipolar Transistors are a combination of the two.
They really are a bipolar junction transistor with a FET connected
between the collector and base. They give many of the advantages
of both types. With the FET, the voltage drop across the drain-source
increases linearly with current. (It is a resistance, after all.)
With the Bipolar and IGBT, the voltage drop is almost flat with
changes in current, usually around 1.5 V. Regular bipolar junction
power transistors require a base current about 1/10th of the collector
current. With 100 A transistors, that amounts to 10 amps the control
circuit needs to deliver to the base. Darlington transistors have
at least 10 x higher gain, but the voltage drop will be double, a major
disadvantage. The IGBT solves that problem. The gate current required
is zero, once the gate capacitance has been charged.

One other pro/con thing about IGBTs is that, like other bipolars, the
forward voltage drop goes DOWN as they get hot. This effectively prevents
thermal runaway with single devices. But, it makes it a lot
harder to balance current in paralleled devices, as the hottest one
will have the lowest voltage drop, and thus get all the current.
(By comparison, the resistance of FETs goes UP with temperature,
making thermal runaway possible. But, it makes paralleling devices
a breeze, as they will self-equalize their current.)

Jon

"Glenn" wrote in message
...
Thanks for the very nice explanation Jon!
I guess I have been a tech for too long .. I just can't get into staying
current unless it is directly related to the problem I am trying to fix
If Iggy keeps this up I may just have to dust off all the test equip on my
bench and start playing again LOL. It is true what they say about never
going to work in a field that is a hobby. It really takes the joy out of
it in 30 years or so.

Nah... that isn't necessarily so. But it can be. Like Cindy Crawford says
on that furniture commercial, "I only want to do what I'm passionate about."
(Why, oh, WHY couldn't she be passionate about my body????)

If you truly LOVE what you're doing as a hobby, making it a vocation isn't
all that bad. I did fireworks for a hobby for years, then decided to make a
living doing it. It was the best career decision I ever made!

'Pends on what you expect of it.

LLoyd

On Sun, 27 Nov 2005 14:29:41 GMT, Ignoramus18456
wrote:



The only thing that my inverter does not have, is control of power
when electrode is negative, and separate control when electrode is
positive (I think that it is called AC balance). For my inverter, the
absolute value of the voltageand current is the same for positive vs
negative half cycle.

They control balance with duty cycle control, which you can also do.

Yes, but, I think, they could also make current different for positive
vs. negative part of duty cycle.

Varying duty cycle does vary average current in each polarity even
though the instantaneous current magnitude is the same in both
polarites. That's how a Synchrowave works, others maybe different.

With DC pulsing, there is a "background" current level and a "pulsed"
current level but both are of same polarity.