How to wire TWO switches to control polarity

Discussion in 'The Projects Forum' started by rynwmmr, Apr 15, 2014.

  1. rynwmmr

    Thread Starter New Member

    Apr 15, 2014
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    I have a project that I would like to use two small push button style switches, to control the direction of a dc motor.

    The details are a 12 volt DC battery (lawn mower battery), power window motor, not sure on any specs for this motor.

    I do NOT (and can't) use one switch (DPDT). Is there a way to wire this so that two switches can be used, one will make the motor spin forward and the other will make the motor spin in reverse. I don't know if a relay needs to be used, as to protect the circuit from both switches being pressed at the same time by accident. They need to be momentary switches, so when the push button is pressed the motor spins then stops after being released.

    Can somebody provide a list of items needed (switch types SPST, SPDT, RELAYS, ETC.) and a diagram to wire them. THANK YOU!
     
  2. inwo

    Well-Known Member

    Nov 7, 2013
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    I'll look up a diagram that I drew for another project.

    You just need the two switches if they are rugged enough.

    No interlock needed. If both are pressed motor is off.
     
  3. inwo

    Well-Known Member

    Nov 7, 2013
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    Couldn't find an exact match.
    Here's one.............
     
    Last edited: Apr 15, 2014
  4. inwo

    Well-Known Member

    Nov 7, 2013
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    I did find one with bosch relay numbering if switches are light duty.
     
  5. rynwmmr

    Thread Starter New Member

    Apr 15, 2014
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    Thanks for your quick help. I don't know much about this stuff so the diagram is a bit greek to me. Any idea where I can get parts (online) just need two small push button switches and whatever else to make the diagram work?
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    use the second diagram with the relays or make darn sure your switches are rated for the motors current.
     
  7. inwo

    Well-Known Member

    Nov 7, 2013
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  8. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    You need:
    1) Two pushbutton switches, SPST, N.O.
    2) Two relays, SPDT. Automotive relays that are SPDT will work fine, are inexpensive, and available everywhere. You can connect to them using 1/4" spade connectors.

    Not shown are reverse-EMF diodes across the relay coils, and from the motor terminals to +V and -V; without the diodes across the relay coils, the pushbutton contacts will get burned, without the motor diodes, the relay contacts will get burned. Perhaps inwo will add them to the schematic drawing for you.

    We don't know where in the world you are, so it's difficult to suggest where you might find the parts you need.
     
  9. inwo

    Well-Known Member

    Nov 7, 2013
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    [​IMG]Cap and diodes are not necessary for operation. Only for long contact life.
    Often have internal suppression from 85-86.

    [​IMG]
     
    Last edited: Apr 15, 2014
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,526
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    One thing to keep in mind if the motor carries a fairly high load and the inertia is high, then instant reversal before the motor has come to a stop will result in very high motor current.
    And with shorted armature braking in effect, very high BEMF current.
    Max.
     
  11. rynwmmr

    Thread Starter New Member

    Apr 15, 2014
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    I purchased the components needed, two spst n.o. push button switches and two spdt relays, with the numbers shown (87 87a 30 85 86). Is it possible to get a more laymen's diagram to wire this application up. I know the diagram provided should / will work but I don't really understand it to well, this is not my expertise. Thanks in advance.
     
  12. inwo

    Well-Known Member

    Nov 7, 2013
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    Try this scribble...............................................................................................
     
  13. rynwmmr

    Thread Starter New Member

    Apr 15, 2014
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    that is perfect, excatly what I was looking for. Thanks for your awesome help. will let you know how it works
     
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