Control Circuit for an Overhead Crane

Discussion in 'Homework Help' started by Turk, Jan 27, 2009.

  1. Turk

    Turk Thread Starter New Member

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    Good Morning All
    im struggling with a piece of homework set by my tutor .
    He requires me to come up with a control circuit for an overhead crane , that will have the following criteria.
    Forward/reverse
    Up/Down
    Left/right
    must have LIMITS
    must work of a remote station .
    Ant ideas are appriciated thanks ALL.
  2. kubeek

    kubeek AAC Fanatic!

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    I think you just need to find a diagram of single motor control with limit switches, and apply it to all the three motors you need to control.
    Remote location is just longer wires to the control buttons.
  3. KMoffett

    KMoffett Senior Member

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    Can this be a "wired" remote, such as a 6-button pendent on the end of a cable running to the cranes power/motor/control box?

    Ken
  4. Turk

    Turk Thread Starter New Member

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    Yes m8 ..:)
  5. KMoffett

    KMoffett Senior Member

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    Can we assume that these are small DC motors, as you would use in a model crane? For this type of motor's on/off/direction control look into "H-bridges", either solid-state or electro-mechanical relay.

    Ken
  6. Turk

    Turk Thread Starter New Member

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    I think its all factory sort of cranes
    we have been working alot on circuits in the class, how to start a motor in star an switch to delta that sort of thing , im stuggling as to were to put the limit cut off .:confused:
  7. KMoffett

    KMoffett Senior Member

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    Sorry Turk, you're into big, high HP, multi-phase motor control. That's out of my area of expertise (if I can even say I "have" expertise. ;) ) But, I'll be watching.

    Good luck.

    Ken
  8. kubeek

    kubeek AAC Fanatic!

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    First you need to get the general idea how to start & reverse.
    As far as I remember, three-phase motors are reversed by swapping two of the three phase wires, but don´t take this for granted as I don´t know the exact type of your motors.

    You should end up with some diagram, where you have two tri-phase relays, one for forward and one for backward motion. Then you need some circuit to control the two relays and take the limit switches into account.

    Limit switches should be closed when not reached, so you can wire the limit switch in one direction in series with the relay moving the motor that way, so it disconnects the relay when reached.

    You also need to make some protection so that you cannot activate both relays at once or it would short the main AC. You can do this by using DPDT switch so that one half activates one relay, and the other half disables the other one. (again using the NC contact in series with the other relay) This way when you push both, none of the realys gets activated.

    So in total, you should need only 2 power relays, and two DPDT switches to control one motor with end limits.

    btw, is this making any sense to you? :)
    Last edited: Jan 27, 2009
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