Stick to TIG welder conversion

Discussion in 'The Projects Forum' started by gregtomko, Jul 7, 2009.

  1. gregtomko

    Thread Starter Member

    Sep 29, 2008
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    I am converting an old AC stick welder to a DC TIG, nothing fancy, no high frequency arc starting, or square wave or anything. I am just going to rectify the output from the secondary of the welder for DC, and vary the current to the primary with a large triac for remote current control. My question is, I would like to be able to use a microcontroller to drive the triac, a BTA40-800B, which needs a pretty hefty 80ma to drive the gate, so can I use a smaller triac to trigger the large one, and drive the small triac through an optoisolator from the micro? Or is there a better way I am not thinking of?

    thanks for any input
     
  2. gregtomko

    Thread Starter Member

    Sep 29, 2008
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    I have seen schematics using SCRs to vary the primary current, but they have the same gate drive difficulty, and I thought a triac would simplify things. Am I overlooking something, or will the triac be ok?
     
  3. gregtomko

    Thread Starter Member

    Sep 29, 2008
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    Actually now that I looked into it a little more, I am thinking about using one of those optoisolators with a triac output to drive the main high current triac, or am I still wrong about being able to use a triac to drive the primary of the welders transformer all together?
     
  4. gregtomko

    Thread Starter Member

    Sep 29, 2008
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    Just for clarification, I am going to hook up the high current triac just like you would in a dimmer switch for a light bulb, but in place of the diac and potentiometer trigger, I will be using the optoisolator with triac output driven by the micro, for triggering.
     
  5. gregtomko

    Thread Starter Member

    Sep 29, 2008
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    Also I was looking at a APT1221 for the optoisolator, which has a 100ma rated output, which I am thinking would be sufficient to drive the BTA40-800B triac which has a max trigger current of 80ma. Oh yeah, this is going to be powering a 220v welder which runs off of a 30amp breaker.
     
  6. JJAngleton

    New Member

    Aug 21, 2010
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    If you ever got around to finishing your project, let me know. I would also like to convert my 220V AC welder to a tig machine. I understand that for aluminum I do not need DC. Except, a HF arc starter would be nice. Do you know of a quick circuit, maybe using a car ignition coil or a TV flyback transformer and a few transistors for the oscillator ?
     
  7. shortbus

    AAC Fanatic!

    Sep 30, 2009
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  8. marshallf3

    Well-Known Member

    Jul 26, 2010
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    I'd start that way provided the optoisolator would be able to drive the big triac.

    BTW: You're going to end up with a ton of switching harmonics, most of which are going to head directly back into the AC mains. You'll want to filter those out as best you can.
     
  9. BMorse

    Senior Member

    Sep 26, 2009
    2,675
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    This thread is over 1 year old, I doubt the op is going to respond....
     
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