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Powering a 30 - 250 Ampere MIG-welding machine

M E62
Prodigy 70 points

Hi!

I have a big MIG-welding machine which has broken.

I think it is a short-circuit in the transformer's coil(s).

Now, it has a compicated system to adjust the output current.

It is a big rotary-switch, which connect and disconnects parts of the transformer's input-coils.

I can use the core i have, get get new wires and make a 3 x 400Volts to 42 Volts transformer. (It's a three-phase)

I allready have the big rectifier and thick cables, but i need to be able to adjust the output current.

-Is 42 Volts x 3 enough?

-should i use a higher output Voltage?   ...or lower?   -how many Volts?

It use to be about 40 - 70 Volts in MIG-welding-machines, no load and 20 - 30 Volts when the welding machine is in use.

There are big transistor like 100 - 300 Ampere Collector-current, but what about the circut to control the output-current?

-How should i build it?

I think a linear regulator is the best, switching will not work as it should, -am i right thinking so?

Thanks!

  • 0
    Prodigy 5 points

    Hello M E62,
    To replace the brute force transformer method for welding, with an electronic design, is no trivial task.

    Linear regulators can not be used in the main power path because they will waste copious amounts of heat.

    See this TI DESIGN for what it takes to create a welding machine.
    Granted it is Arc Welding but the currents are very similar.


    http://www.ti.com/solution/welding?keyMatch=welding&tisearch=Search-EN-Everything


    And it must be said, 

    Content is provided 'AS IS' by the respective TI and Community contributors and does not constitute TI specifications. 
    See terms of use.

  • 0 in reply to Ed Walker
    Prodigy 70 points

    I see.

    -Should i use a switching regulator?

    ...or should i solve this problem in an other way?   -how?

    What if i use powerful fans and 2, 3 or more transistors?

    -Would it work?

  • 0 in reply to M E62
    Prodigy 5 points

    Hello M E62,
    Your best bet is to try and find the transformer on one of the resale internet sites.
                     Or attempt to rewind it yourself.
    The resistance of the windings is very important for limiting current while maintaining an arc.



    From an electronic standpoint, the reference design I showed has the required power blocks.
    An electronic design will need to mimic what the old proven transformer method does, while also providing optimization of the welding process that the transformer cannot do.

    1. Power Factor Correction switcher on the input. This allows you to draw full power from the AC line.
        You may not need 3 phase if you use PFC. 

    2. PFC output then goes to another switching stage that provides the lower voltage for welding.
        The second stage also provides isolation, as the existing transformer does, for safety reasons.

    3. Linear regulators will not work, it is that simple.
        TI does not make Linear Regulator circuits to support 100's of Amps.

    The only solution TI has for you is the reference design previously presented.
    Good luck with your project.