relay to reverse polarity of 12v current on timer

Discussion in 'General Electronics Chat' started by liv2plant, Jun 5, 2009.

  1. liv2plant

    Thread Starter New Member

    Jun 5, 2009
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    Hello, all
    I am a complete newbie, so please bear with me!
    I am trying to make an automatic control system for a 12 vdc linear actuator. The actuator is used to close and open a sliding door on a chicken coop. The actuator has an integral stop switch so that when it reaches the end of its limit for travel it automatically shuts off. So - in the morning an AC timer will supply current to a 12vdc adapter, which will send current to the extended actuator, which will contract and open the door. When the actuator is completely contracted it will turn off in response to its integral stop switch. At dusk, the timer will turn again and - if I have put a device in place that will reverse the polarity of the DC current - the actuator will extend and close the door. It will repeat the process every 24 hour.
    The problem is the device that will reverse the polarity of the DC current automatically. How do I create it?
    THANKS!!!
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,747
    759
    DPDT Relay would be suitable for it

    Rifaa
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    1,728
    You need to supply a bit more information about your linear actuator's wiring.

    If the limit switch opens the circuit when the end of travel is reached, just reversing the polarity won't help, as the limit switch will still be open.

    There's also a problem in using a simple timer, as daylight hours change - and if there's an interruption in power, the timer will wind up at some random time setting.
     
  4. liv2plant

    Thread Starter New Member

    Jun 5, 2009
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    We can manually adjust the timer, no problem there.
    When we manually switch polarity on the actuator (by reversing the wires of the DC power supply) the actuator switches direction just fine.
    The actuator has 2 wires.
    I think a relay is the answer, but can't figure out how to wire it to do the switching. We tried with 2 SPDT standard automotive relays but could not make it work.
    Thanks for all of your help!
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    Do the timer's contacts close, and stay closed until the evening when they open?

    Or do the contacts close twice a day?

    Either way, it'll be ugly. In the first case, the relay's coil will be energized all the time during daylight hours.

    In the 2nd case, contact bounce will present a problem.

    It would be a lot easier if the limit switches were externally accessible.
     
    Last edited: Jun 17, 2009
  6. liv2plant

    Thread Starter New Member

    Jun 5, 2009
    4
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    Now we are thinking that a DPDT latching relay is the answer. Does that make sense?
    Thanks!
     
  7. liv2plant

    Thread Starter New Member

    Jun 5, 2009
    4
    0
    The time is a simple AC timer that will come on for 15 minutes in the morning and 15 minutes in the evening. A 120 vac to 12 vdc adapter will be plugged into it. So whenever the timer turns on, the adapter will put out 12vdc power, always of the same polarity.
     
  8. rballard

    New Member

    Aug 3, 2009
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    Did anyone ever supply a solution to the problem presented in this post? I have the exact same issue and would be interested if there is a solution.

    Thank You,

    Russell Ballard
     
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