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AC to DC welder

Discussion in 'General Electronics Discussion' started by Jay1947, Jan 25, 2016.

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  1. Jay1947


    Jan 25, 2016
    Hello All, I am a new guy with a question. I have a 125A flux core wire feed welder that I would like to change to DC output. Now it is not much more than a large transformer. The problem is to weld flux core wire the wire should be DC and not AC. The welder output is 27V no load, 60 to 80 amps with a peak of 125amps. I can get a 200 amp bridge rectifier and a 10k uf 80v cap on ebay quite reasonably. The 200amp rectifier is very available even if not really required.
    Does this sound like a workable approach ? Do I need a choke ? Thanks Jay
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Care to look at this writeup?
    You may not need the capacitor bank at all. The author uses 2*23000µF = 46mF. Charged to a peak voltage of 27V and discharged by a current of 80 A, the capacitors will be drained after 15 ms (t=[C*V]/I). Your mains is 60 Hz, after rectifying the capacitors are re-charged every 8ms. Therefore the capacitors will be discharged to about 1/2 of the peak voltage every cycle. There is not much smoothing here.

    As far as I remember the importance in DC welding is in the uniform direction of the current, not in the smoothness.

    Note that you're dealing with quite dangerous levels of power! Although 27V may not sound much, it's the energy in P=V*I that can wreak havoc. Have an expert check your work.
  3. Minder


    Apr 24, 2015
    Typically MIG welder etc have just a large choke in series with the torch conductor.
  4. debe


    Oct 15, 2011
    This is a DC MIG welder I had. Just has a bridge rectifier & a choke after the rectifier. SIP MIG.6.JPG SIP MIG.7.JPG
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