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Slow Releasing Table Contactor

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  • Slow Releasing Table Contactor

    I've got a chassis in which the table contactor is slowly releasing instead of dropping as soon as it is supposed to. Will change out relay, but curious why this happens. Is it residual magnetism in the coil?

  • #2
    Re: Slow Releasing Table Contactor

    It can be residual magnetism as well as a sticky plunger or the combination of both. Also could be the contacts are sticking or the built in return spring is usually broke on one or both sides.

    Trash it, if budget allows.

    Triac

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    • #3
      Re: Slow Releasing Table Contactor

      Thanks Triac. Springs okay & contactor actuates and releases okay when actuated manually by lifting plunger.

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      • #4
        Re: Slow Releasing Table Contactor

        If you've checked the springs and checks for binding then, yes it would likely be residual magnetism.

        Note that the residual magnetism only lasts for a very short time (less than a second), so that's why you don't detect it when manually lifting and releasing the plunger.

        This is caused by the outer magnetic core poles from wearing down (the two places where the moving armature/plunger touches the core of the contactor).

        Since the outer poles are worn, the air gap that is normally present between the centre poles reduces (between the top of the plunger shaft inside the coil and the main housing) and starts to touch causing residual magnetism.

        I haven't ever tried fixing these - we just replace them (and with new-style contactors).

        If you've got contactors with crappy contacts, or burnt coils, you could swap the armature and/or core with a better one.

        Theoretically, it would be possible to file down the centre pole (on the armature) to reintroduce the air-gap. However, if the gap is a few microns too large, the contactor will buzz (and eventually burn out) - the same as what happens if the outer poles get dirt/crap on them and create an air gap on them. As I said, I have never tried this - might be interesting if you could be bothered.

        Andrew.

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        • #5
          Re: Slow Releasing Table Contactor

          Never saw a contactor stick from "residual magnetism". Saw a lot of them stick from pieces of contact that fly off when the contacts break and arc, and carbon from the arcing that builds up around the center post... occasionally one will get a wire under it that acts like a 'helper spring' that keeps it closed up momentarily until the wire sags down a bit. There's so much contact spring and weight on the center post that the contactor is almost forced to break when the coil power turns off.

          When rebuilding a contactor, it's a good practice to drop out the center post and run a small flat file down through the hole in the coils to dress the sides of it. You'd be surprised how much black gunk you can get out of them if they haven't been cleaned for a while. I file them lightly, and then spray a little ECG electronics wash or delicate parts cleaner down thru to clean out the dust and gunk.
          <span style="font-style: italic">Educatio est omnium efficacissima forma rebellionis</span>

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          • #6
            Re: Slow Releasing Table Contactor

            For $55 or so, you can buy the solid state replacements from Bowltronics. (make sure to specify run buttons) they come with a 2 year warrantee!!!

            Best $55 I ever spent.

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            • #7
              Re: Slow Releasing Table Contactor

              Originally posted by JimDorsin:
              For $55 or so, you can buy the solid state replacements from Bowltronics. (make sure to specify run buttons) they come with a 2 year warrantee!!!

              Best $55 I ever spent.
              <font size="2" face="Verdana, Helvetica, sans-serif">I agree....except for the run buttons.....not needed at my joint....no interlocks.

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              • #8
                Re: Slow Releasing Table Contactor

                I do a lot of front end work, and I like to have control of the table and sweep when I have (previously) turned off the switches on the BE box. 50 lane center, lowest curtian wal I have ever seen, only walkways at 1 and 50, and I am an old fat man, too hard to climb...lol

                These boards will run (just like the contactors) when the switches are off.

                Comment


                • #9
                  Re: Slow Releasing Table Contactor

                  JimDorsin said :
                  I do a lot of front end work, and I like to have control of the table and sweep when I have (previously) turned off the switches on the BE box.
                  <font size="2" face="Verdana, Helvetica, sans-serif">i also like the run buttons sticking out the front of the chassis as well for that reason

                  Comment

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