Snubber circuit design -- max voltage (TIG welder)

[Ignoramus26745]

I am trying to come up with an intelligent process of selecting
components for the snubber circuit.

I am getting very paranoid about possibly frying my welding machine
with this inverter circuit. I would like to avoid that at all costs.

I have arrived to formulating my goal as: having a circuit such that
under no circumstances there would be voltages anywhere within the
welder that would exceed voltages that would normally exist _without_
my inverter.

Otherwise, I am afraid, some existing components may be damaged as
they were possibly not designed for such higher voltages.

Therefore, the first step would be to try to measure such max
voltages. The manual specifies max voltage as 150V. I think that it
would be good to try to limit voltages to 150V, that would be most
conservative.

That brings up a question, how to select components.

1. I would select the snubber caps such that the voltage generated
during commutation dead time would not exceed 150V (and should ideally
be about 100V). It seems that, assuming a 1 uS dead time and 360A
welding current (pessimistic assumptions for my 200a welder), 4 uF of
capacitance should take care of it. I hope that I can select resistors
such that there would be no dead time at all, but I think that I can
get to be no more than 1 uS dead time.

2. I would also add a varistor set to start conducting at (having a
breakdown voltage of) 150V. Here I am somewhat confused. Varistors
have different ratings, DC, AC, etc. What varistor rating should I
choose so that it breaks down at 150V.

If my post makes any sense at all, I would like to hear the answer to
my question in point 2. Thanks.

i

 

[Winfield Hill]

Ignoramus26745 wrote...

I am trying to come up with an intelligent process of selecting
components for the snubber circuit.

I am getting very paranoid about possibly frying my welding machine
with this inverter circuit. I would like to avoid that at all costs.

I have arrived to formulating my goal as: having a circuit such that
under no circumstances there would be voltages anywhere within the
welder that would exceed voltages that would normally exist _without_
my inverter.

Otherwise, I am afraid, some existing components may be damaged as
they were possibly not designed for such higher voltages.

Therefore, the first step would be to try to measure such max
voltages. The manual specifies max voltage as 150V. I think that it
would be good to try to limit voltages to 150V, that would be most
conservative.

That brings up a question, how to select components.

1. I would select the snubber caps such that the voltage generated
during commutation dead time would not exceed 150V (and should ideally
be about 100V). It seems that, assuming a 1 uS dead time and 360A
welding current (pessimistic assumptions for my 200a welder), 4 uF of
capacitance should take care of it. I hope that I can select resistors
such that there would be no dead time at all, but I think that I can
get to be no more than 1 uS dead time.

2. I would also add a varistor set to start conducting at (having a
breakdown voltage of) 150V. Here I am somewhat confused. Varistors
have different ratings, DC, AC, etc. What varistor rating should I
choose so that it breaks down at 150V.

If my post makes any sense at all, I would like to hear the answer to
my question in point 2. Thanks.

I do fault your posts, because usually it's not clear exactly what
configuration you are considering. That's because we must attempt
to make "schematic" drawings from your incomplete or slightly vague
verbal descriptions, which is not satisfactory. I suggest that you
learn to make simple ASCII drawings and start illustrating your posts.
You can also learn how to simplify your circuit and thereby show only
the relevant parts in your post. Then we can give you accurate and
useful analysis and advice. And we'll all be happy.

 

[Ignoramus26745]

Ignoramus26745 wrote...

I do fault your posts, because usually it's not clear exactly what
configuration you are considering. That's because we must attempt
to make "schematic" drawings from your incomplete or slightly vague
verbal descriptions, which is not satisfactory. I suggest that you
learn to make simple ASCII drawings and start illustrating your posts.
You can also learn how to simplify your circuit and thereby show only
the relevant parts in your post. Then we can give you accurate and
useful analysis and advice. And we'll all be happy.

Winfield, I will try. I have a web page where I put some materials
regarding that inverter project. I will place a drawing there.

i

 

[Winfield Hill]

Ignoramus26745 wrote...

Winfield, I will try. I have a web page where I put some materials
regarding that inverter project. I will place a drawing there.

The web page is a good idea, but it's been filled with empty
pages, which is worse than useless, because it's a big turnoff.
I suggest it's not a good idea to have empty placeholder pages
(unless marked *on the link*), because people click on them and
after a few, they won't come back. I'm not going back until
you tell us there's stuff to see, OK? OK.

 

[Ignoramus12686]

Ignoramus26745 wrote...

The web page is a good idea, but it's been filled with empty
pages, which is worse than useless, because it's a big turnoff.
I suggest it's not a good idea to have empty placeholder pages
(unless marked *on the link*), because people click on them and
after a few, they won't come back. I'm not going back until
you tell us there's stuff to see, OK? OK.

There was one empty page called Components, I removed it for now. I
did not yet make a drawing/schematic of where my inverter will be
placed in the system.

i

 

[Winfield Hill]

Ignoramus12686 wrote...

There was one empty page called Components, I removed it for now.
I did not yet make a drawing/schematic of where my inverter will
be placed in the system.

Perhaps I should have included "nearly-empty" pages in my comment.