Polarity switching relay for linear actuator

Discussion in 'The Projects Forum' started by wallisp, Nov 15, 2014.

  1. wallisp

    Thread Starter New Member

    Nov 15, 2014
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    Hello!
    I wish to use a linear actuator for a web remotely activated dog door. My idea is to use a Wemo outlet to power the linear actuator, but I want to be able to use the actuator in both push and pull which means reversing the polarity of the power. The linear actuator has limit switches to turn itself off when the door is opened and closed. So I would like to find a relay that will switch polarity to the actuator every time the Wemo is turned on. The actuator is 12vdc. Can someone point me to such a thing? Thanks!
     
  2. MikeML

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    Oct 2, 2009
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    Sounds like y0u need a toggle flip-flop and a relay, or a toggle made out of relays (takes three, IIRC). Both have been discussed on these forums previously. A little quality time with the Search feature might be productive...
     
  3. NorthGuy

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    Jun 28, 2014
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    Two SPDT relays. Mottor connected between common contacts. NC contacts connected to -. NO contacts connected to +. Drive one relay to open or the other to close.
     
  4. wallisp

    Thread Starter New Member

    Nov 15, 2014
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    Thanks so much. I'll give that a try.
     
  5. MikeML

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    Dont you have a single pulse source which is supposed to alternately move the actuator in and out? If so, the solution from NorthGuy requires that a toggle switch be thrown every time you want the actuator to move. Hence you need a flip-flop toggle circuit...
     
  6. MikeML

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    My Bad, for never having heard of a Wemo. It might have helped if the OP told us what a Wemo is...
     
  7. NorthGuy

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    Jun 28, 2014
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    With this schematic, the relay is energized during the entire period while the door is open.
     
  8. MikeML

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    The limit switches are inside the actuator (only a red and black wire protrude from it) , so move the limit switches to the horizontal wires either side of the motor...
     
  9. NorthGuy

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    Also add diodes accross newly moved limit switches. The diodes are part of the actuator too.
     
  10. MikeML

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    I bought a similar 12Vdc actuator to operate a 16' swing gate. All I know is that when the actuator reaches either limit, the motor stops and current drops to zero. When you reverse the polarity, the motor runs the other way until it hits the opposite limit switch... I took advantage of this by monitoring the current to the actuator, and detect the zero current to know that the actuator in fact reached its limit..
     
  11. wallisp

    Thread Starter New Member

    Nov 15, 2014
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    Thanks for all the replies. I was originally hoping that there is an off the shelf component someone knew of and could point me to that I could simply add between the actuator and power supply. The component would flip output polarity every time input voltage was supplied. I think I understand the circuitry needed now with all the help and will build the component if nothing is simply available OTS. Thanks gain.
     
  12. crutschow

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  13. wallisp

    Thread Starter New Member

    Nov 15, 2014
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    Thanks! Looks like just what is required.
     
  14. NorthGuy

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    It also costs 200 times more than a flip-flop :)
     
  15. crutschow

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    But it's off-the-shelf and requires no additional power. ;)
     
  16. MaxHeadRoom

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    Jul 18, 2013
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    The 711 relay shows no longer being manuf.?
    If I am in a position where an expensive relay is an option, for about the same price I look at a Smart Relay, several manuf make them, timers, latches and real time clocks are some features.
    plus they have all the I/O and logic you need for small systems or controls.
    Max.
     
  17. MikeML

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    Just get a DPDT relay with a 120Vac coil and a AC line cord (scavanged from an old computer). Black and White wires in the line cord go to the coil terminals. The 12V wiring goes to the six contact terminals as shown above. Keep the 12V wiring separate from the 120Vac wiring. You will have to mount it inside an enclosure, so get a small box.
     
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