12v central locking motor reverse relay

Discussion in 'The Projects Forum' started by mittler.a, Sep 29, 2012.

  1. mittler.a

    Thread Starter New Member

    Sep 29, 2012
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    Hi,

    I want to make my number plate on my bike movable for stunt riding - it would be in the way, i.e. the rear wheel touching it.

    I have a 12v central locking motor that will do the job. With normal polarity applied for 2-3 seconds it will move the number plate to visible position and reverse polarity to flick it under the pilion seat.

    What I need now is a relay that will reverse the polarity and apply timed power for 2-3 seconds every time I push the button switch.

    Can anyone tell me what circuit I could use here? I am pretty new to building my own circuits so any help would be much appreciated. Thanks!

    Alex
     
  2. strantor

    AAC Fanatic!

    Oct 3, 2010
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    ah the old license plate hider circuit. First time I've heard a "legitimate" reason for one. Well you need a timed relay. you can find 12V timed relays on ebay for cheap but when you see how big they are, I don't think you will be happy. Of course, if your motorbike is actually a lowered pickup with obnoxious neons, exhaust, and stereo system, you won't care much about the size.
     
  3. NFA Fabrication

    Member

    Aug 12, 2012
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    Would you be OK with having 2 buttons? I think it would be simpler to do with a 556 dual timer with each side set to 3 seconds. One of each of the timers in the 556 triggers each position. I see a way to do it with one button, but it gets more complicated. Someone will probably chime in with a better solution...
     
  4. mittler.a

    Thread Starter New Member

    Sep 29, 2012
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    :) thats it, its all about size. need something tiny in this case.
     
  5. mittler.a

    Thread Starter New Member

    Sep 29, 2012
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    dual buttons would do, yes. the only reason for the relay is I don't want 12v cords all around the bike just for switching this.
     
  6. strantor

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  7. mittler.a

    Thread Starter New Member

    Sep 29, 2012
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    strantor thats a really good idea! However this would still require me to run 3 battery cables to the switch and back to the motor. What do I do there?

    Thanks, Alex
     
  8. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Ah, I missed this part:
    so you just want one wire going to the switch and one coming out. Well, that's still 2 wires; only one more with the toggle/limit switch setup. If you want to do it easy peasy without putting together a board full of components, what you are going to need is called an impulse relay. These things are not cheap. cheapest I've seen is ~50$ and it's pretty clunky.

    Not really worth it IMO to add an expensive heavy thing to a stunt bike just to save running one wire. you know you can cut a piece of extension cord to run up to your switch - that's just one cable with 3 conductors in it.
     
  9. mittler.a

    Thread Starter New Member

    Sep 29, 2012
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    OK agreed lets keep it at 3 cables then :)
    Will the switch suggested above actually cut the power when pressed or give power when pressed?
     
  10. strantor

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    Oct 3, 2010
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    no, the toggle only directs the power in one of 2 directions; one of the 2 limit switches will cut the power.
    [​IMG]


    EDIT: to be clear, I'm referring to a maintained 2 position toggle switch, not a pushbutton
    http://www.alliedelec.com/search/productdetail.aspx?SKU=70131541
     
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  11. mittler.a

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    Sep 29, 2012
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  12. strantor

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    yeah but you'll need diodes across them like I drew. Before I can tell you yes, that switch and this toggle and these diodes will work, I need to know how many amps the motor pulls.
     
  13. mittler.a

    Thread Starter New Member

    Sep 29, 2012
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  14. mittler.a

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    Sep 29, 2012
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    Finally found it:

    No-load&load current:1.5A±5%&3A±10%
     
  15. strantor

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    Oct 3, 2010
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    DOH!
    That's no good. I've bought one of those exact actuators before; it's a chinese door lock solenoid. It pushes or pulls depending which way you put power to it, but when there's no power, it floats. the system would work as drawn, but might keep drifting down and retracting, drifting down and retracting, as you drive.
    I thought you were referring to something more like a servo, that stays put when there's no power to it.

    You could try eliminating the limit switches, which would give it constant power in either direction to hold it in place, but I don't know if it's rated for constant power. That would also be a drain on your battery, and maybe on your performance too.
     
  16. mittler.a

    Thread Starter New Member

    Sep 29, 2012
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    It would hold in place as I've built a mechanical solution that will make sure it stays in place until the actuator pulls it away.

    What is the use of the diode, and which one should I buy? Thanks!
     
  17. strantor

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    COORECTION: I drew the limit switches as being normally open. They should be normally closed!
    the diode is because:
    A. A diode allows current to flow in one direction and not the other - a check valve basically.
    B. when the motor is between one end and the other (in transit) both limit switches are closed, meaning power flows through both of them.
    C. (refer to drawing) Let's say that current is flowing from left to right through the motor and the motor is spinning clockwise and then limit switch B (right) is tripped - current can no longer flow - it cannot go through the limit switch and it cannot go around the limit switch through the diode. the motor stops.
    D. Now you flip the switch and send current the other way around; now it CAN go around the limit switch (through the diode) so it does, and the motor turns CCW (or "anti-clockwise" for Europeans), and lifts off the limit switch, and travels until it reaches limit switch A, at which time the cycle repeats (when you flip the switch the other direction again).
    E. if the limit switches were not there, it would work once and then never again. it would run up against a limit switch and then have no way to reverse when you flip the switch the other direction

    you can use whatever rectifier diode you can find that's rated 5A or better and 20V or better. don't pay attention to the Vf parameter.
     
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