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Hobart 120 loss of power tripping breaker

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  • Hobart 120 loss of power tripping breaker

    Hey yall, I have been using this wire fed welder for a while now with no problems. Yesterday however in the middle of a weld it seemed to lose penetrating power and start to almost stab at the metal instead of give a consistant arc. The welds are very sperattic and look like ape snot now. Also as I was testing it to try and trouble shoot it started to trip breakers after a couple minutes of welding. I have only used it with flux core and it has done well up until now. Any help you guys might provide would be great.
    Thanks,
    Mark

  • #2
    Bad rectifier? Hobart expert can tell you how to test it and find your problem here or over phone. Will need volt ohm meter also called a multimeter.

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    • #3
      Forgive my ignorance i have never had to work on my welders before other than the basics. What does the rectifier look like or does it have another name? I have a manuel with a parts list and can't seem to find it.
      Thanks again.

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      • #4
        Depends on how old your welder is for what your rectifier looks like. I could be 2 or more diodes mounted on aluminium sheet metal heat sink. Older rectifier could be stack of 2 or more square sheet metal with space between with diode in middle. It is on output side of the main transformer changing AC current to pulsating DC current. After that or along side is one or 2 large capacitors to smooth out the pulsating DC. They can give big shock even after power is off. On the other output wire from that transformer is what looks like a smaller transformer but just a coil called a choke. This choke tunes how fast welding current reacts to electrode wire short circuit to work up to about 200 times a second while welding in short circuit transfer mode.

        Newer rectifiers would have a diode as pictured at top right of this web page.
        http://en.wikipedia.org/wiki/Rectifier

        Web search diode tests and capacitor tests. Words and pictures or you tube video.

        You can down load Hobart MIG welder manuals from link at top of this page. Illustrated parts breakdown is near last pages of manual. Circuit diagram in some manuals is about middle of manual.

        After you know what parts look like and basics of using multimeter call Hobart for easy voltage tests to find and verify problem.

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        • #5
          10-4 on that. Yeah did some testing today. The rectifiers, i read somewhere on here, are not suposed to be open both ways when testing ohms. Mine are open both ways so i believe this is what is wrong. I will however call Hobart and make sure I am testing correctly.
          Thanks Roger big help

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          • #6
            Testing diodes in place need to disconnect one of the 2 wires so your test is isolated to just the diode. As you describe your test results you found bad diodes. Biggest reason to be sure you are replacing bad parts is not waste time and money waiting for parts not needed. Cross check part numbers on diodes and order them on line at Digi-key. http://www.digikey.com/


            The large dangerous capacitors should have bleed resisters to safely bleed stored electrical energy so can't get shocked. Bleed resistors are shown in some Hobart manuals. Best to just keep hands away from those capacitor terminals until they are proven not charged.

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