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Millermatic 350P breaker trips

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  • Millermatic 350P breaker trips

    Yesterday AEP Texas had a huge spike in our area and my shop has three phase. I had around 350 on the big leg and the requisite 115 or so on the other two. My shop was built in the 1950's and still has those big cylindrical fuses daisy chained between stations. Anyway, I had a big door motor go out, (I thought), then the air compressor (I thought) so when I turned on my Millermatic 350P, which is set to run on three phase, it blew a couple of those fuses. Long story short, AEP fixed the power spike, I replaced the blown cylindrical fuses and all of my three phase machines are working, except the Millermatic unit, which pretty much immediatly flips it's breaker. I rolled it across the shop to another outlet, same thing. I get a few lights, the MM350 comes up then pop, the breaker is out. My manual doesn't lead me to any internal circuit breakers or resets. I've yet to inspect my power cord but I think if I had an arc, then I wouldn't even get that far. Any further ideas from the members would be much needed and appreciated. JDMinerals

  • #2
    It happens so fast, that if the unit was on,the on/off switch is fried, igbt preregulator circuit is trashed ( that's what makes the breaker trip)


    • #3
      Thanks for the advice. When I looked it up its a component inside the inverter and from what I can tell it should be a part that I can change out. I'm sorry, I'm new to this forum so don't take offense, is this a problem that has cropped up before? In other words, would this IGBT be the only item that takes the brunt of a power companies spikes? By working backwards, with the power spike from AEP, what actually occurred is that my high leg was at 340, my middle leg had partially failed and was around 35 amps and the left leg was normal. So the machine was seeing some really lopsided power. Regardless I really appreciate the time to answer this, thanks. JDMinerals


      • #4
        Unless its on warranty, and play dumb on how the unit got fried. It's likely going to cost quite alot to repair. (couple $$ grand)


        • #5
          More than likely, getting a voltage spike has popped the restistors on your interconnect board. If that happened then your SR1 is probably deep fried. If you open up the case on your machine, on the right hand side toward the bottom is where you will see the 3 legs of your incoming power coming from the main contactor which is located on the left side of the machine toward the bottom in the back. Where they bolt in is where your SR1 is. Right next to each incoming leg terminal is the restistors that I'm talking about. They are usually green, about the size of a quater and about 1/4 inch thick. Check to see if any of them are blown.