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Thread: AC Motor rotational control with PLC

  1. #1
    Join Date
    May 2018
    Location
    Flanders, Belgium
    Posts
    2

    AC Motor rotational control with PLC

    Hi,

    I have a pretty simple electrical question for a conveyor belt (3phase 400V). I have an AC motor that can only be turned in SCADA. And only in one direction. The motor drives a transport belt that moves wood chips. Sometimes the belt is blocked because of a wood chip. This is 90 percent of the times solved by just turning the transport back a bit and then moving it back forward. A frequency drive is not necessary.

    At the moment the only way to move it backwards is by switching the wires in the electrical cabinet and then turning the motor via teamviewer in scada. Which is not very practical. I want to install 2 switches at the conveyor belt:
    • Bistable switch that switches between auto and manual. If it is in manual you can not turn it with the scada for safety reasons.
    • Monostable switch with 3 positions: Forwards, 0, backwards


    See my drawing below:
    https://drive.google.com/file/d/1Mzp...ew?usp=sharing

    I think this simple system is the easiest way to do this. However I am not sure if this is save. Is this system possible? Are their safety issues that I am overlooking? Is it possible to short circuit this system?

    Thank you for reading this!
    Hopefully I placed this thread in the correct folder. Sorry in advance if I didn't.

  2. #2
    Join Date
    Sep 2008
    Location
    UK
    Posts
    11,896
    Quote Originally Posted by Kloë View Post
    Hi,

    I have a pretty simple electrical question for a conveyor belt (3phase 400V). I have an AC motor that can only be turned in SCADA. And only in one direction. The motor drives a transport belt that moves wood chips. Sometimes the belt is blocked because of a wood chip. This is 90 percent of the times solved by just turning the transport back a bit and then moving it back forward. A frequency drive is not necessary.

    At the moment the only way to move it backwards is by switching the wires in the electrical cabinet and then turning the motor via teamviewer in scada. Which is not very practical. I want to install 2 switches at the conveyor belt:
    • Bistable switch that switches between auto and manual. If it is in manual you can not turn it with the scada for safety reasons.
    • Monostable switch with 3 positions: Forwards, 0, backwards


    See my drawing below:
    https://drive.google.com/file/d/1Mzp...ew?usp=sharing

    I think this simple system is the easiest way to do this. However I am not sure if this is save. Is this system possible? Are their safety issues that I am overlooking? Is it possible to short circuit this system?

    Thank you for reading this!
    Hopefully I placed this thread in the correct folder. Sorry in advance if I didn't.
    Don't see any particular problem but I would want to electrically and mechanically interlock the two contactors.
    Si hoc legere scis nimium eruditionis habes.

  3. #3
    Join Date
    Aug 2004
    Location
    Northern illinois
    Posts
    16,900
    IMO the "relays" would need to be HP rated. Why not just replace the existing motor starter with a reversing starter. Probably simpler in the long run.
    Bob

  4. #4
    Join Date
    May 2018
    Location
    Flanders, Belgium
    Posts
    2
    Quote Originally Posted by petersonra View Post
    IMO the "relays" would need to be HP rated. Why not just replace the existing motor starter with a reversing starter. Probably simpler in the long run.
    A reverse starter seems indeed a lot simpler. I need to look up a bit how it exactly works and how to dimension it, but I should be able to manage :-)
    https://drive.google.com/file/d/118f...ew?usp=sharing
    Thank you for the help!

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