Magnetic Contact instead of a relay?

Discussion in 'General Electronics Chat' started by Kinoton, Feb 11, 2015.

  1. Kinoton

    Thread Starter New Member

    Jan 20, 2014
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    Hi , I am converting a 3ph motor to run from a single phase inverter. All works fine but I would like to use remote switches to run the inverter instead of the buttons on the inverter itself. It makes sense to use the buttons on the machine (a cinema projector ) . Looking inside the machine there appears to be two magnetic contact switches in line with the 3ph to the motor. Using the inv I am currently by passing these switches but if I apply single ph to the terminal strip inside the machine and press the start button , one contact closes followed by the second. I think what is designed to happen is that the first one closes and sends 3ph through some resistors to provide a soft start , and then a timer cuts the 2nd mag contact in (and the 1st out) when the machine is at speed. My question is could I use one of these contacters to provide a run signal for the inverter. Obviously I will disconnect the original 3ph arrangement as this is no longer needed. Sorry so long winded!
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If by inverter you mean VFD you should not have any contactor between VFD and motor, one can be used on the input side for E-stop or power off.
    If it is a VFD, all control should be done by the low level input terminals set up for this reason.
    These do not need anything as large as a contactor but either normal P.B.'s or small control relays can be used.
    Max.
     
  3. Kinoton

    Thread Starter New Member

    Jan 20, 2014
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    I see what you mean; wouldthe contactor divert 230vac into the control inputs of the VFD?
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Normally the contactor is used only on the power input supply side for the reasons I mentioned.
    It would not be used for the on/off low voltage control at all, this would be done with separate low voltage control, usually ~24vdc supplied by the VFD itself..
    Max.
     
  5. Kinoton

    Thread Starter New Member

    Jan 20, 2014
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    Thanks for that.
    So if I wanted to use the buttons on the machine (start N/O) stop (N/C) I would need a relay to maintain the run signal ? I don't think the VFD I'm using has a built in 24vdc supply (omron sysdrive 3gvxv)
    Cheers
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Page 2-14 of the manual, you just need contact closure P.B.'s the supply is internal.
    Wire the buttons direct to the input terminals and the common.
    There are two ways to do it, you can use one two position switch if need be, one way to run, the other stop.
    Max.
     
  7. Kinoton

    Thread Starter New Member

    Jan 20, 2014
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    Thanks Max. Yes , I've done something similar to that in the past using a locking PB but I wanted to make use of the ones that are already on the machine , which I believe are n/o momentary contact for the run button and n/c for the stop . If I wire these to the terminals then would it only run while I hold the run PB in ? Jon
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    It is a little vague but it may be that by setting N02 and N36 you can set momentary input on start and stop setup.
    It would be easy to test.
    Max.
     
  9. Kinoton

    Thread Starter New Member

    Jan 20, 2014
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    Thanks Max , I will check that , much appreciated ! Jon
    ciated
     
  10. JWHassler

    Member

    Sep 25, 2013
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    'a little vague' is faint damnation! That's a data-sheet designed to piss-off an electrician.
    The diagram for 3-wire control is on page 2-14.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    After reading through it I believe the 2 wire momentary will work.;)
    Max.
     
  12. Kinoton

    Thread Starter New Member

    Jan 20, 2014
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    Hi Max
    As you say the manual is vague indeed. Where can you see the info regarding the parameters that will allow momentary contact to start the inverter? Thanks again , Jon
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    2-14 I believe Standard input is start & stop inputs momentary.
    Also 10-2 n2=0?
    And page 5-18 for multi-function setup, which you may not have to go into, try the combo's out and you should get the mom start stop i believe.
    Max.
     
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