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Thread: Convert AC welder to DC welder???

  1. #1
    gary350 Guest

    Default Convert AC welder to DC welder???

    I have an old Lincoln AC welder, I wish it was DC. I have seen things for sale I believe they are called converters for a welder. Is this something that changes AC to DC?

  2. #2
    Join Date
    Apr 2011
    Location
    Boise, Idaho
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    86

    Default Bridge rectifier

    I am not sure what you mean by converters.

    A full wave bridge rectifier will "convert" AC into DC. 4 large diodes, rated at 100 plus amps each, and able to stand a few hundred volts should do the trick. 2 should be cathode to stud, and 2 anode to stud. Mount each set of diode pairs into 2 large electrically isolated heat sinks and connect the two welding leads, one to each of the heat sinks. The heat sinks are the plus and minus DC outputs. Connect the 2 AC leads, one tied to the pair of diode leads on each heat sink and you should be all set to weld with DC. You might want to include a fan and a nice enclosure.

    wikipedia has a schematic http://en.wikipedia.org/wiki/Diode_bridge

    Your local Craig's list probably has some AC/DC buzz boxes, Lincoln or Miller for a decent price, that is probably not all that much more than you will spend building the rectifier set up, though if you are a good scrounger you can do the rectifier pretty cheap.

    I dare say that there is probably a thread on this site about this very subject.

    gordon

  3. #3
    Join Date
    Sep 2008
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    2,137

    Default

    Ironnut, I tried that some years ago and it really does not work well at all. We had some large diodes at work and used them to build the full wave rectifier but the problem is that while it does indeed change the current to DC it is a pulsating DC that is nearly as bad as AC current for welding. The current would have to be smoothed out considerably to work well, possibly by using large capacitors but that might present an electrocution hazard?

  4. #4
    Join Date
    Aug 2003
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    872

    Default Welder

    Check with a local fab shops and see if they have any 'dead' welding machines on hand. The old machines will have a large diode bridge assembly, possibly a suitable choke and associated switch gear. Any dead diodes can be easily replaced. The only value of the old units is in the copper windings and bus bars.

    JRW

  5. #5
    Join Date
    Apr 2011
    Location
    Boise, Idaho
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    86

    Default

    Quote Originally Posted by radkins
    Ironnut, I tried that some years ago and it really does not work well at all. We had some large diodes at work and used them to build the full wave rectifier but the problem is that while it does indeed change the current to DC it is a pulsating DC that is nearly as bad as AC current for welding. The current would have to be smoothed out considerably to work well, possibly by using large capacitors but that might present an electrocution hazard?
    I can't say I ever tried building a rectifier for a welder. The one inside of the the little Miller buzz box didn't have any capacitors and it seems to weld just fine. Miller may be using an inductor as a filter but I would have to pop the top on the buzz box to see what else is in there.

    I did convert a car alternator into a portable gas engine driven welder and it works quite nicely. Admittedly the 3 phase full wave bridge rectifier I built has a lot less ripple in its output. Plus with the alternator spinning around 10 grand, the ripple frequency is a kilohertz or so. When you are tig welding with this rig the arc "sings" at a fairly high pitched whine. If the engine slows down the frequency of the whine goes lower. The rig will burn 3/32" 6010 rod in fine shape. If you push the rpm of the engine a bit it will run 1/8" acceptably. Noisy as hell but in my more financially challenged days it was all that I could afford. Besides I learned a great deal about 3 phase power and had fun building it.

    gordon



    gordon

  6. #6
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    SW Michigan
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    Default

    I have a Miller (I think) that converts AC to DC. Just hook your AC leads to it & it has plug ins so you you can change from positive to neg. If you need a model number let me know. I bought it with a Century high freq Tig unit & never used either.
    "The things that will destroy America are prosperity at any price, peace at any price, safety first instead of duty first, the love of soft living and the get rich theory of life." Theodore Roosevelt

  7. #7
    Join Date
    Jun 2009
    Location
    Western NC
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    54

    Default Tried that also on my 2 welders

    I used 4 diodes in a bridge circut and couldnt tell any difference, after reading some articles on the web I fould out you need to add a inductor. After
    adding one it worked better but not like I thought it would, serveral years later I tried it on my Miller thunderbolt 225 and it worked great. I don't know why but it just don't work well on the Linclon 225 buzz box. But I do know you need a inductor coil, I got mine from a junked 3 phase welder.

  8. #8
    Join Date
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    Default

    The Craig's list here often has teh Lincoln "tombstone" in eitehr an AC or AC/DC type. The AC/DC are usually a hundred bucks more.

    The inductor is almost a necessity.... it should let you strike the arc better, and keeps the arc from extinguishing when voltage goes to zero 120 times a second

    I suppose you could use AC rods on plain rectifier DC..... they seem to have materials in the flux coating to keep the arc from extinguishing as easily.

    When we did AC in class, I found it to "purr" along and did a very nice weld.... seemed to be smoother than DC, almost like buttering bread in comparison.... but we had just finished doing overhead welding, and nearly ANYTHING would have seemed easy after that.

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