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  • sajurcaju
    started a topic Shopmaster blows breaker MIG only

    Shopmaster blows breaker MIG only

    I have a Miller Shopmaster 300, s/n KD408963. My manual is January 1993.

    It has worked fine until recently. Now it will sometimes mig weld, sometimes it pops the breaker. The breaker pops right when I pull the trigger, before the wire strikes an arc. I looked at my liner, it had a couple of minor kinks so I replaced it, no change in symptoms. I was welding 1/8" steel, it will weld fine for a bit, pause, pull the trigger again and the breaker pops.

    Stick welding (reverse polarity, 170A) works fine.

    I am using a 50A breaker which has always worked for me. I changed to the 50A circuit for my plasma cutter (different breaker), same problem.

    Advice will be greatly appreciated.

    Steve

  • sajurcaju
    replied
    Lemo gets the gold star. It was (still) the breaker. Cruizer gets huge appreciation for all the details; he's also right, just not exactly what he thought. Thanks guys.

    The new symptoms came with the new 80A breaker, which I somehow didn't realize (it was new...). When I switched to my other 50A circuit, I got the old symptoms back. In the process, I realized that I had an unused (i.e. new 3 years ago) 50A breaker in another spot on the panel. I connected to it and now have no welder problems.

    Long term, I expect the problem will come back. When it does I'll buy a larger breaker from a more reputable source. The 80A came from Amazon/"TradeBelow"; it was cheap, but I sent it back as not working right. It did not work as well as my 50A breakers.

    Funny thing, a friend of mine just put in two 50A breakers (new). One of them was bad. Just a coincidence, I'm sure.

    Steve
    Last edited by sajurcaju; 12-29-2013, 03:29 PM.

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  • cruizer
    replied
    OK, you figure it out, works fine on 20 volts, blows breaker on 24 volts. Obviously drwing more power. Power you don't have....

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  • sajurcaju
    replied
    I've got plenty of history on 50A breakers with no problems. I don't think you're on the right track with the 100A breaker.

    Steve

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  • cruizer
    replied
    Or, get more power to your shop, as this unit takes a 100 amp breaker.

    Leave a comment:


  • sajurcaju
    replied
    Ten minutes later, it is a little different.
    Before (by mistake) I had the output contactor switched on. With it set to remote, and the gun voltage at 20V, wire feed at 350 ipm, it welds fine. When I increase the voltage to 24V (machine is on), the instant the wire hits the work piece, the breaker pops. I tried this twice; 20V is fine, 24V pops the breaker.

    Frustrating situation. Maybe time to pick a repair shop.

    Steve

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  • sajurcaju
    replied
    The breaker was easy to try, so I put in an 80A breaker. I couldn't even turn on the main switch on the welder without popping it. Tried it with the other circuit (50A), same result, can't blame the breaker. The welder was set to 29V and the wire feeder to 400 ipm.

    Back to being plugged into the new 80A breaker. If I set the welder to 29V and the wire feed to 300 ipm, I can turn on the main switch and the fan runs. If I change the wire feed to 400 ipm and then try to turn on the main switch, breaker blows every time. So it sure looks like something in the wire feed.

    I'll measure the pins in the Amphenol connector and see if they match up to the documentation, especially a possible swap between A and G. Additional advice will be greatly appreciated.

    Steve
    Last edited by sajurcaju; 12-14-2013, 12:10 PM.

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  • Miller Lemo
    replied
    Cruiser,

    With 240 volt power on this unit it is required to have a 100 amp input breaker. Now I realize that he probably is not using the machine to its full rated output but I believe the intermittent issue is caused by the undersized breaker. I personally have the same machine and feeder running .035 solid wire in my own shop. Early on I had a similar issue with tripping the breaker in CV mode as I only had a 50 amp installed and it did the same thing. I had to increase the breaker size to 60 amps to eliminate my problem. The 50 amp worked for a while but over time it started doing exactly as he described.

    I know with a 60 amp I am still undersized from what is recommended but it has not been a problem any more. I did this at least 10 years ago.

    Sajurcaju you will have to verify your input box and system will handle a larger breaker.

    Regards,

    Lemo

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  • cruizer
    replied
    Yes there is protection provided A & G were wired correctly, however if they are wired in reverse, you'd have no protection, but the unit would still work. It all connects to the primary transformer. And thats where I think the problem is. (control cable)

    This surge also wears out the breaker.

    I see it all the time from either factory made cables or from half wit cable building techs.

    Leave a comment:


  • sajurcaju
    replied
    This is an intermittent problem. I did some welding last weekend, making a bracket. Some days are better than others.

    When I was shorting A+B, I checked the pins with my meter. All were ok then (didn't blow the breaker either).

    What I was asking is how the signal wires would flip the breaker. Am I looking for a short to ground? It seems like the machine would have something smaller than a 50A breaker protecting signal wires.

    Steve

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  • cruizer
    replied
    Like I mentioned crossing A & B on the machine does the same thing as hitting the trigger on the gun. Soooooo, hitting the trigger hits the breaker, crossing a & b does nothing. This makes the problem with the feeder and cable. Now all the feeder is using is a,b,g. Test em

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  • sajurcaju
    replied
    Lemo, I'm running on 240V single phase. Good point about inrush, I hadn't thought of that. I'll look for a larger breaker. I have tried it on a different 50A circuit with the same results. The breaker box was a new install 3 years ago, for what it's worth.

    Cruizer, I really appreciate the detail you've helped me with here. On the control cable, what am I looking for? I'm having a hard time picturing what could go wrong in a control line that would pop the breaker.

    It shouldn't be a big deal to just replace the control line, end to end, but I like to get to the bottom of these things. I should probably start with the short end attached to the wire feeder.

    Thanks,
    Steve

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  • cruizer
    replied
    Lemo, we already figured that he had a low breaker, however, triggering his gun blew the breaker imediately, jumpering "A" and "B" did not. Really no difference if his feeder was ok. I believe the problem is with his control cable to his feeder.

    Leave a comment:


  • Miller Lemo
    replied
    sajurcaju,


    Question for you?

    What is your input voltage you are using with the 50 amp breaker? One thought I had with reviewing your thread here was if the breaker is undersized and your running this on a lower voltage the in-rush current over time will weaken the breaker. The in-rush is caused by charging the cap bank in the CV mode. The current required to do this is much higher than you may think for the sort period of time.

    Make sure your breaker is properly sized for the input voltage you are putting into it.

    Let us know how that works for you.

    Lemo

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  • sajurcaju
    replied
    Things stay the same

    Cancel that last post. What happened was the preflow knob got moved to several seconds while I was cleaning up. This was long enough that I didn't think the trigger was making it feed. With preflow on minimum, the wire feed works like normal.

    While I was trying this out, the breaker popped once more. Reset it and did some welding, no additional problems.

    So I'm back to where I started, intermittently blowing the breaker.

    When I jumpered A+B on the connector, I didn't hear anything like a contactor connection. Is this right? I know the gas solenoid isn't going to switch, but it seems like there should still be a contactor go off in the main box.

    Steve

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