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Sharp 12x40 electrical problem

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  • Sharp 12x40 electrical problem

    The wiring was completed in my shop at work, and everything works fine except the Sharp lathe, which I ran immediately prior to it's move.

    The lathe has a master power switch, and a motor power switch, which energizes a contactor sending power to the forward and reverse motor switches, which when actuated by a lever on the apron, send power to the forward and reverse motor contactors.

    Plug the lathe in (208V 3 phase) turn the master power switch on. Turn the motor power switch to on, main contactor buzzes. Touch the test button in the middle of the contactor and it snaps closed. Cycle motor fwd-rev lever to either position and the corresponding contactor will buzz until you "help" it closed.

    I checked voltages at the transformer, and the 2 primary wires that are connected (out of 3) which I'll call #1 and #2, have 117.5 across. If you measure between #1 and #3 you get 234.8. The secondary side shows 58.6 volts at the terminal block and the contactor in.

    All connections and fuses are good. It seems a clear case of low voltage on the front end of the contactors, but nothing has changed since the lathe was moved. I literally ran it right before the riggers arrived and watched it the whole 10 mile trip from the University of MD to our shop.

    Any ideas?
    "Lay on ground-light fuse-get away"

  • #2
    I am not an expert on electricity but you mentioned 208 volts. Was the machine previously operating on 220volts? That difference might be the problem. JIM


    • #3
      It sounds to me like you don't have 3 phase power. What you described sounds like 240 single phase with a neutral. Line 1 to ground reads 120v, Line 2 to ground reads 120, Line 1 to Line 2 reads 240. 3 Phase power should read 208 between any one to any of the other leads.

      I'd be careful (avoid) trying to run it until you have someone check this out for you.

      "When it comes to paradigms ... shifts happen" - Alain Rossman


      • #4
        The shop was wired by a talented master electrician this week. I have 208V 3phase in 4 locations; at a disconnect box for the 5hp-2stage-80 gallon compressor, and 3x 30 amp 4 blade twist lock outlets for the 16" DoAll bandsaw, Bridgeport mill, and the offending lathe. The last 3 tools are all on the same run, and the first thing I tested was plugging the lathe into the bandsaw's socket and vice versa. I was glad I hadn't shortened the cords when the new plugs were installed.

        The saw runs perfectly, as do the Bridgy and the compressor. There's 207 or so between the legs testing at the outlet.

        Once you "help" trip the 2 contactors, the lathe runs perfectly smoothly and powerfully. It's getting 208 3 phase into it's terminal block as verified by my VOM.

        As I mentioned, I ran the machine, verified correct operation, unplugged it, had it moved, (which I observed), placed it, and it sat abput a month until it received power yesterday.

        The question I've been unable to answer is: Do the Mitsubishi S-A11 contactors in this machine need 58, 117, 208, or 234 volts to close? I can't find a data sheet on these since they were made in the 80's.

        I've eliminated everything except a low power to the actuation side of the contactors. I don't see how it could have changed.

        I may resort to calling Sharp on Monday to see if they can offer any help.
        "Lay on ground-light fuse-get away"


        • #5
          My suggestion would be to check the normally closed contacts in the system.To me it sounds like an open or an intermitant might be present or a faulty connection to ground.
          I just need one more tool,just one!


          • #6
            low control voltage

            Sounds like the control transformer is wired for 440.
            Check the wiring schematic on the transformer and wire it
            for 220ish. I'm guessing the contactor coils need 100-120 volts.
            They are marked on the contactors.
            If the transformer was wired for 440 then you also need to check
            how the motor is wired at the motor ...... it may also be on 440.


            • #7
              I replied over at PM..... but it sounds like a wiring problem......
              CNC machines only go through the motions.

              Ideas expressed may be mine, or from anyone else in the universe.
              Not responsible for clerical errors. Or those made by lay people either.
              Number formats and units may be chosen at random depending on what day it is.
              I reserve the right to use a number system with any integer base without prior notice.
              Generalizations are understood to be "often" true, but not true in every case.


              • #8
                So, it turned out the astrophysicist (literally) who wired this lathe back in '84 connected the 3 hot legs to red-black-green and ground to white. My master electrician connected the new plug to the cord with red-black-white hot and green as ground, as it should be.

                That gave me 117 rather than 208 at the transformer primary side/56 at the secondary that powers the contactors. No click.

                I swapped white and green, got 208 at the primary side, 117 on the secondary, and a really nice running lathe.

                Everything in the shop is running well now, and I get to order everything else this week.

                $25k and the MSC, Enco, Metals Express, Grainger and Travers catalogs spread out on my desk. Makes up for any number of miserable coast to coast trips on the redeye.
                "Lay on ground-light fuse-get away"


                • #9
                  Jeez, ya lucky ya not dead.


                  • #10
                    I did consider doing it while wet and naked with the line hot, but reconsidered and unplugged it first and did the work with tools while I was fully clothed.
                    "Lay on ground-light fuse-get away"