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Anyone Ever Add A DC Rectifier To Old Forney AC Crackerbox ?

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  • Anyone Ever Add A DC Rectifier To Old Forney AC Crackerbox ?

    Just another dumb question for all of you folks with a lot more experience than me.

    I have an old 1970s Forney AC welder that still works well and wondered if any of you had ever added a rectifier bridge to an old AC machine for DC use ?

    If you have how did it work and was it worth it ?

    I scavenged a rectifier off of a 300 amp DC machine in a salvage yard and all of the diodes check out to be good, so the cost is not a problem, but wondered how well it would work.

    I would appreciate any ideas you all might have !

  • #2
    You've already got the diodes, hook it up & try it!
    Let us know how it works.
    Professional Auto Mechanic since 1974
    My own shop since 1981
    Cya Frank


    • #3
      You already have the diodes this may give you some ideas on enclosures, venting etc.

      Hope I helped


      • #4
        I wouldn't make an enclosure yet...Just hook em up!
        See if it works OK... If it does, then make it safe & neat!
        Professional Auto Mechanic since 1974
        My own shop since 1981
        Cya Frank


        • #5
          Wow! What a great project!

          You could make that as simple (rectifiers wrapped in a heat sink) or as fancy (Heat sensitive fan switch, capacitor bank to give smooth DC, overtemp switch, SCR firing circuit, etc.) as you want. How cool. I've been thinking of building my own High Freq box to complement my inverter. Keep us posted on the project and lots of pics.

          Good luck!

          Ammonia refrigeration tech
          Trailblazer 302 (yes, it's new)
          Millermatic 180 w/Autoset
          HF-15 High frequency
          XR15 w/Push-Pull Gun
          Victor O/A, DeWalt, North mask

          "A professional knows what to do. A craftsman knows why."


          • #6
            I very much appreciate the input and works of encouragement !

            The only thing I wonder about is the low 60 cycle frequency of the AC side of things.

            I have an old Miller Bluestar 2E DC welder that generates AC and then rectifies it to DC, but I am not sure of the frequency.

            The generator seems to be 4 pole so it can generate 60 cycle power at 1800 RPM for 120 volt AC.

            When welding the engine speed increases to about 3600 so with 4 poles the frequency would be 120 cycle I suppose.

            The higher the frequency the smoother the DC output I would think.

            It may be a while before I complete this project as the location where I plan on using the old AC machine does not have any utility service yet and it may be sometime after the first of the year before utility power is connected.

            I'll let everyone know something as soon as I can.

            Thanks again to all !


            • #7

              I've got an old Forney that came in mint shape and with the original documentation. I believe it list an external rectifier for it, so it sounds do-able.


              • #8
                I don't know if I would automatically suppose that the hertz cycle went up with engine speed.
                Miller 251...sold the spoolgun to DiverBill.
                Miller DialArc 250
                Lincoln PrecisionTig 275
                Hypertherm 900 plasma cutter
                Bridgeport "J" head mill...tooled up
                Jet 14 X 40 lathe...ditto
                South Bend 9" lathe...yeah, got the change gears too
                Logan 7" shaper
                Ellis 3000 band saw
                Hossfeld bender w/shopbuilt hyd.
                Victor Journeyman torch and gauges
                3 Gerstner boxes of mostly Starrett tools
                Lots of dust bunnies
                Too small of a shop at 40 X 59.


                • #9
                  Don't know if this helps but here it is anywaysClick image for larger version

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                  Hobart Mega Arc 5040DD (with built in air compressor)
                  MM Passport Plus with Q-gun

                  sold MM 251

                  There are only 2 tools needed in a tool box. 1) Duct tape to fix any thing that moves that isn't supposed to. 2) WD40 to fix anything that doesn't move but should.


                  • #10
                    The electric machines like that are all 60 cycle, doesn't change with DC, thats what the input power is.