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  • Fusible Links Blown

    I have a Miller CP302 that has blown its fusible links F1 and F2. What would cause this to happen? Before I change them, I would like to find out why they blew.

  • #2
    HELLO ….. HELLo ….. HELlo ….. HEllo ….. Hello ….. hello
    ECHO ….. ECHo ….. ECho …. Echo ….. echo

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    • #3
      Hi, I don't have a CP-302, but do have it's older version, the CP 300. Are you referring to the two circuit breakers on the front of the machine, tied to the 110V and 24V circuits that feed your feeder through the remote receptacle? If so, then it likely was your wire feeder. Did you change anything on your wire feeder when they blew?

      Edit: those fusible links are between your transformer output and rectifier assembly (big octagon looking metal thing between your transformer and fan. First, check for resistance across your output leads. If they are shorted, then you likely have a bad component in your rectifier assembly. It could be one of the capacitors across your SCRs and diodes, but it's probably at least one of your SCRs or diodes. There should be three diodes and three SCRs (look just like the diodes except they have a little wire coming out, probably the three of them on the top half of the metal octagon). Do a diode test on each one (they look kind of like bolt heads with a big wire sticking out the top, the SCRs also have a little wire that goes to the circuit board at the top inside of your machine). If these pass, there is a diode/resistor/varistor assembly that connects the two metal pieces of the octagon. Hopefully this makes sense, it would be easier with pictures... If the resistance across the leads is not high, maybe you were burning 1/16+ wire at 800+ ipm?

      Jon
      Last edited by jjohn76; 10-07-2019, 08:02 AM.

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      • #4
        Thanks for the post. See photos of fusible links. Excellent suggestions. Out of town today, I will report back tomorrow.

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        • #5
          Those aren't fusible links, they are fuse elements somebody punched holes in the ends of and misused.

          They were designed to function inside a powder filled tube to protect them from vibration. Once vibration works on a fuse element it fractures and then blows itself.
          Also fuse elements are ONLY accurate in current limitation when operating in the environment they were designed to occupy, such as a powder filled tube.

          Portable Heliarc machines often employ a "water fuse" to insure coolant flow thru the torch. That 10 Amp element surrounded by flowing coolant will pass 300 amps without blowing. No coolant the element cooks off before the torch is damaged.

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          • #6
            Originally posted by Tanks_Alot View Post
            I have a Miller CP302 that has blown its fusible links F1 and F2. What would cause this to happen?
            Too much current would be my guess.

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            • #7
              Originally posted by Helios View Post

              Too much current would be my guess.
              2 quick ways to determine that.
              1 would be to meter the draw across the open element
              2 would be to substitute a incandescent light bulb of appropriate voltage in place of the cooked element.

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              • #8
                Those look almost exactly like the fusible links inside my miller DC rectifier. Weird.

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                • #9
                  Originally posted by ryanjones2150 View Post
                  Those look almost exactly like the fusible links inside my miller DC rectifier. Weird.
                  That's exactly where they go in the Miller CP-302 - right before the rectifier.

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                  • #10
                    I popped mine a couple years ago, the max output is 150 amps, I was pushing 225 through it. Oops.

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                    • #11
                      Originally posted by ryanjones2150 View Post
                      I popped mine a couple years ago, the max output is 150 amps, I was pushing 225 through it. Oops.
                      Those are each listed as 350 amp 250V links in the manual, but they're also listed as a recommended spare part... I guess they're meant to go out? It's still probably worth checking the output rectifier.

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                      • #12
                        I have a different machine that I popped mine in. I ended up going to a local industrial electric supply for them. They were maybe a few bucks a piece.

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