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Snubber circuit design -- max voltage (TIG welder)

Discussion in 'Electronic Design' started by Ignoramus26745, Nov 2, 2005.

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  1. 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
     
  2. 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.
     
  3. 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
     
  4. 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.
     
  5. 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
     
  6. Ignoramus12686 wrote...
    Perhaps I should have included "nearly-empty" pages in my comment.
     
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