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  1. #1
    Join Date
    Sep 2007
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    Default Milling machine control panel issue

    Hey guys
    Was using my milling machine last night and it just stopped working half way through a cut.
    Never happened before. Pulled the panel off to see what's going on and check it all out with a multimeter.
    Everything seems ok as far as I can tell with my prodding. What's funny is that it still works if I manually press one of the big relay blocks (Where my screw driver is pressing down in the pic).

    Anyone able to offer any advice as to what to try next.
    I have checked all the switches including emergency stop, for continuity and they seem ok.

  2. #2
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  3. #3
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    Well the problem is in the control circuit. Or maybe the coil in a contactor has died. Probably a deceased coil.
    Light red, the colour of choice for the discerning man.

  4. #4
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    Following on from RC suggestion, it could also be the small transformer that takes line voltage down to 12 or 24 volts usually to power the relay coils. Alan.

  5. #5
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    Did it cut out like there is no lights, or did the motor just stop?
    Will it run in the other direction?
    Is it possible it cut out by overheating and reset itself by the time you pressed the contactor?
    Is it single phase or 3 phase?
    It's possible the contactor you pressed will turn the motor one way and the contactor beside it will turn it the other way. The little blocks on top of the contactors are aux contactors and its possible they act as an interlock so the motor can't be driven forwards and backwards at the same time (they stop both contactors from actuating at the same time). Those Aux contactors are likely to be wired in series with the coil of the other contactor, so they are a candidate for failure too. Assuming there is only one fault, if the motor does not run backwards or forwards using the operator buttons on the control panel, then the aux relays are not the fault.
    The top left red wires, two that come together and are marked 0 on a yellow tab, are likely to be feeding the contactor coil for one motor direction. Did you get volts appear on them when you had the switch pressed? You would need to know which way the motor turned when you pressed that contactor, otherwise you wouldn't know which direction needs to be pressed to send volts to that coil. You'd also need to know what volts to look for on those coils. If you look on the side of the contactor there is usually a code which you can look up to say the coil volts etc.
    If there was the correct volts to the coil, its a contactor issue, if not, look elsewhere.

  6. #6
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    mmm is that an electrical insulated screwdriver your using in that pic...if the answer is no...dont stick it where it may not be wanted...you may get a bit more than a shock

    as you seem to have a green indicating light I reckon RC is on to it...control voltage ok but coil open circuit on contactor

  7. #7
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    Quote Originally Posted by sossity View Post
    Is it single phase or 3 phase?
    single ph going by the terminal strip

  8. #8
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    Sep 2007
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    Default

    Thanks for the reply guys. It's helping alot.
    So the machine just stopped while I was cutting in forwards.
    I've tried in reverse and I get nothing either.
    The lights don't come on at all. But when u press the button below the aux contact machine works both ways.

    I'm going to test the aux contacts today.

    image.jpg

  9. #9
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    Are you certain there's volts getting to the switches on the control panel? Since you have no volts to the coils on the contactor (the LEDs are hard wired to the coils by the look of it) I think C-47 has the best guess so far. Both aux relays would need to fail to stop both directions (or at least both contacts on the aux relay) which isn't impossible, just less likely. On the Aux contactor, when you pressed the main contactor down, I take it the Aux was pulled with it? it has no coil of its own, it just clips onto the main contactor and should get pulled down. I can see one is working in your pictures, how about the other one?

  10. #10
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    Sep 2007
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    I checked volts to the switches on the control panel, and they are Def. getting volts.
    I agree that both Aux relays would need to fail for both directions to stop working - which is very unlikely.

    Yes the Aux was pulled down with it on both when i manually pressed them.

    I've called around to get a Chint Aux Contact but seems no reputable dealer in Aus sells them. The closest I could get was a Sprecher + Schuch one, which may fit...
    I do have the belif that its not the Aux Contact however and am suspicious with Sossity and C-47 that its the transformer.

  11. #11
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    is there a pic of the wiring diag?

    what is voltage across terminals 11 and 12 at bottom of transformer..(the black thingy to right of the 2 contactors) one has a wire marked 0... cant read the other...this I believe should be 24V..if no 24v check the following.

    On the top of the tranny is a terminal strip marked PE, 1, 2 & 3 with 2 wires marked L & N....what is voltage across L & N..use extreme caution as it should be 240V

  12. #12
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    Just check for volts across the contactor coil, if you have volts but the contactor doesn't pull in, then it's most likely a faulty coil, Isolate the power, disconnect the coil and measure for continuity across the coil, my first guess would be it's failed open cct.

    If you don't have volts across the coil, then trace the control voltage circuit, check first for any interlocks, like e-stops and travel limits. If still no volts, then buzz the control transformer.

    Ray

    Edit, I see I cross posted with Eskimo. I hesitate to suggest it, but, second thoughts, did you accidentally bump the e-stop? Don't laugh, I've seen it happen.

  13. #13
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    Quote Originally Posted by RayG View Post
    Just check for volts across the contactor coil, if you have volts but the contactor doesn't pull in, then it's most likely a faulty coil, Isolate the power, disconnect the coil and measure for continuity across the coil, my first guess would be it's failed open cct.

    If you don't have volts across the coil, then trace the control voltage circuit, check first for any interlocks, like e-stops and travel limits. If still no volts, then buzz the control transformer.

    Ray
    I was then going to ask to check voltage at wire marked 0 on top of contactor and to terminal 12 which should be -24V?
    if volateg when turned then its the coil.

    is that a fuse?...in the thingy to the right of the terminal strip..that red round thing..i think its a glass fuse or similar?

  14. #14
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    Yep, that's a fuse. Checked that already, it's still alive.

    I'll run all those checks you guys have suggested and post back tonight - Im away from the machine now but really want to get back to the house to test!

  15. #15
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    I have the same unit as you. My E-stop broke and would not release.

    Dean

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