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Weld outputs on generator to power 240v power source.

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  • Weld outputs on generator to power 240v power source.

    Might not be possible but I'm not an electrician so looking for some input. I'm setting up a trailer to be a mobile shop. I have a hobart champion 16 and trying to power a miller shop master 300. Plugging into the 240v on the generator seems to be too underpowered, and pops the breakers on the hobart pretty quick. I know my breakers are weak so I'll be replacing those soon.

    My question is, can the weld outputs on the hobart be used to supply the 240v power for the shop master? Concerned the hertz and/ or the voltage may not be right to do that, just know it can supply plenty of amps so want too see if it's possible. The hobart does have ac weld output and the shop master is single phase. Any input would be great.

  • #2
    What function of the shop master are you using that the hobart won't do? You can run a wire feeder straight off the hobart, at least from the manual I'm looking at. For TIG, picking up a new, efficient inverter-based unit might be an easy solution to your problem.

    The weld outputs will be at weld voltage, not AC voltage, even though the frequency may be correct. You'd need to use a large transformer, probably pulled from a CV welder (so a couple hundred pounds or so), to step the CV weld voltage up to AC voltage. But, you wouldn't actually get any more power out. According to the voltage/current graphs in the owner's manual, there's only about 4000-8000W (depending on settings, and the settings you'd need to use are on the low end of that) available on the weld outputs, minus losses in your DIY step-up transformer, while you have a solid 8000W on the AC outlets. And trying to parallel them, even if the phases match, won't give you more power, because 16hp * 70% efficiency = 8000 watts - that is, you're only going to get 8000W out of that onan engine no matter which windings you pull it from.

    Replace the breakers, especially if you know they're bad. The 240V one should be 35A according to the manual. You can probably put in a 40A for welding load duty cycles without risk to the machine.

    Check your governor setting. Should be 62hz/3720rpm at no load. Maybe bump it up just a hair over that.

    Make sure the fine power control is turned all the way up.

    Check AC output voltage. If low, check RPM, fine power control, and all the parts in the field circuit.


    • #3
      Why do you think the breakers are weak? That's a rare diagnosis.

      No, you "can't" use the weld terminals for AC electrical supply. The engineering involved to even attempt it would be harder than acquiring the larger generator or more efficient inverter-based plug-in machine.
      Last edited by MAC702; 12-31-2022, 06:42 PM.


      • #4
        That's about what I was thinking, extra parts to make it work would equal a bigger machine cost wise.

        So far I've just tried running a wire feeder off the shop master. I can run the feeder off the hobart but i want to be able to run mig and tig off the shop master in the trailer so i don't have to run multiple leads inside from the truck. Just having one power cord running in would be simpler.

        I know the breakers are weak because even on the 120v side they will pop sometimes with a 9 amp grinder. I have a new set already just need to install them.

        Thanks for the input, I'll swap the breakers and see what that does then maybe start hunting for a bigger machine.


        • #5
          If you’re not needing the Hobart for a welder and using it just to power the other welder and tools, why not change out the Hobart for a proper generator?


          • #6
            The shop master is a 300 tranny machine isnt it? Those are a 100A service machine, maybe more. Prolly take a machine 3x or better just to get it to light off. You wont have either if you keep fooling with crap like this.
            Last edited by Sberry; 01-01-2023, 01:20 PM.


            • #7
              Ya its a transformer machine. Researched it more last night and I'm going to just run my feeder and tig off the hobart for now and look into getting some newer inverter based machines that aren't so power hungry. Would take a monster generator to power the shop master and that's just not worth it. Thanks everyone for the input though, helped to make it clear what direction to go.


              • #8
                What feeder and tig machine are you planning to run?


                • #9
                  Would like to have a millermatic 211 and a dynasty 200dx, but funds aren't there for them right now. Currently have a model 60 feeder and a hf-251 arc starter with a cool mate 3 for tig.


                  • #10
                    So you're using the second machine just so you have a working foot pedal for tig?


                    • #11
                      The hf-251 just provides high frequency for arc starting so I don't have to scratch start, and it has the solenoid to start/ stop gas flow.


                      • #12
                        What materials, thicknesses and environments is your work?


                        • #13
                          I mean, the only advantage the shop master provides is a foot pedal?


                          • #14
                            So you just have an on/off switch linked to the 251?

                            What do you normally weld on?


                            • #15
                              The pedal goes to the 251 then from that to the shop master, so I have full control of amperage. The shop master, when it has enough power supplied to it, has more output capability then the hobart does. 300 amps vs 210 dc, 225 ac on the hobart. On cv the shop master does 26-28 volts i think vs the hobarts 20 volts. I have a 14 pin wired into the hobart, I just need to get the right rheostat in the foot pedal to work right with the hobart. Miller has a 1,000 ohm rheostat and the hobart needs a 10,000 ohm.

                              Most of the time time I'm welding 1/8" to 1/4". Now and then will have some 1/2" to weld but so far that's not too common. Did need the shop master cranked up for that though. I work on steel, stainless and aluminum.