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Thread: Miller Challenger 172 tripping breaker

  1. #1
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    Miller Challenger 172 tripping breaker

    I have had this machine since new. Started welding as usual set on 1/4" metal using .035 flux core. My 20 amp breaker tripped after a few seconds. Pulled wire out of gun, pulled trigger and tripped again. Reset breaker and runs fine until trigger is pulled. I pulled the cover off, and tried it again, short pulls of the trigger and it sparks near a relay at the back of the machine, btw the drive motor turns when triggered but not for long. Any thoughts? TIA

  2. #2
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    Jun 2008
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    Re: Miller Challenger 172 tripping breaker

    Quote Originally Posted by Danbury5123 View Post
    I have had this machine since new. Started welding as usual set on 1/4" metal using .035 flux core. My 20 amp breaker tripped after a few seconds. Pulled wire out of gun, pulled trigger and tripped again. Reset breaker and runs fine until trigger is pulled. I pulled the cover off, and tried it again, short pulls of the trigger and it sparks near a relay at the back of the machine, btw the drive motor turns when triggered but not for long. Any thoughts? TIA
    How old is the unit and how much usage has it had? What internal circuit breakers does it have, any? Might there be a buildup of dirt or metal shavings near the relay?
    If you disconnect the gun and cable (but not the control wiring), does it act the same? Any difference if the ground cable is also disconnected?

    Do you have, or can you download a schematic for the machine? If so, for the sake of making the work of helpers here easier, can you post it?

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  4. #3
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    Re: Miller Challenger 172 tripping breaker

    You may have a shorted weld output rectifier diode D1 or D2. The relay could be the main contactor with a shorted diode resulting in the spark you see.
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  6. #4
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    Re: Miller Challenger 172 tripping breaker

    I found the problem, I pulled the wires off of the drive motor, pulled trigger and breaker still tripped. Removed the lower side cover and looking around I found 2 insulated wires that have been touching probably since new. They had melted the coating and shorted to one another. Separated and working great!! Thanks to everyone who commented. I will upload a picture soon.

  7. #5
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    Re: Miller Challenger 172 tripping breaker

    Good job.

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