12v timed reverse polarity relay

Discussion in 'The Projects Forum' started by rballard, Aug 9, 2009.

  1. rballard

    Thread Starter New Member

    Aug 3, 2009
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    I've read quite a few posts on reverse polarity and relays but everything I can find uses a manually operated switch of one type or another to activate the circuit first one way and then the other. I need to have a timer in between the battery and the circuit so I don't have to be present to turn the power on. Let me explain my project.

    I need to activate a door twice a day at preset times. I need the door to open in the morning and stay open all day, then close in the evening and stay closed all night. I have a 12v battery, a timer and a 12v motor that will open the door with polarity one way and close the door with reversed polarity. What I need is something that will reverse the polarity in the evening when the timer comes on to close the door. The timer has one positive wire and one negative wire so the voltage comes out of the timer the same way every time.

    The motor does not have an internal limit switch. However it would be limited in run time by the timer. ie: Since it takes about 30 seconds for the door to open and/or close with the motor and set of gears I am using, the timer would turn the motor on everyday at 6:00am for only 30 seconds. Then the timer would turn the motor on again at 9:00pm every night for only 30 seconds.

    It would kind of go like this: Battery -----> Timer -----> Magic Black Box (Relay?) -----> Motor/Gear Module.

    At 6:00am the timer passes current thru from the battery to the "Magic Black Box" for 30 seconds, which turns the motor clockwise for the 30 second period it takes to open the door.

    At 9:00pm the timer again passes current thru from the battery to the "Magic Black Box" for 30 seconds, but this time the "Magic Black Box" reverses the polarity and the motor turns counter clockwise for the 30 second period it takes to close the door.

    Any help would be much appreciated.

    Thank You
    Russell Ballard
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Can we have continuous battery drain of about 20μA for logic? Would recommend using limit switches on door, with just timing the door & timer will eventually get out of sync.
     
  3. rballard

    Thread Starter New Member

    Aug 3, 2009
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    Ok, thanks. Do you have any idea what to do about the relay to get the polarity to reverse each time?

    Russell
     
  4. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    First, what timer do you have? Is it the one which runs the motor for 30secs or the one which gives the output at 6am and 9pm. This helps decide what part is necessary.

    I dont think it is a good idea to do this without limit switches. With a timer, you either will have the door not closed properly or jam it into the door frame.

    For reversing a motor, can be done in 2 ways.

    1. By a single input.
    This uses a single relay and runs the motor in one direction when an input is given to the relay and in the other direction when no input is given. I dont think this is what you need.

    [​IMG]

    2.By Double relay and double Input
    This uses 2 relays and runs the motor in one direction with input to one relay and in the other direction with input to the other. This one has the added facility to stop the motor by either supplying an input to both at the same time or by supplying no input.This is similar to an H-bridge but doesnt have the brake facility which an H-bridge has.You will need a circuit like this.

    [​IMG]


    I had designed a circuit using this a few days back for a curtain runner. It depends on daylight sensing to open and close the curtain automatically. It has limit switches and would close and open doors properly.You can use it as it is if it is ok for the times,i.e, at dawn and dusk. Not at 9pm. Or you can take the second half and give it to a circuit which provides the -ve or +ve pulse at 6am and 9pm ..

    [​IMG]
     
  5. rballard

    Thread Starter New Member

    Aug 3, 2009
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    That looks like a great answer, thank you. I'll study it and see if I can figure it out. Reading circuit diagrams is not something I am used to, but I think if I study it a while I can get it.

    I'll let you know if I get it done.


    Thank You

    Russell Ballard
     
  6. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    If you decide to make something, you must know the basics even if you dont know how to design them. Understanding itself is a great thing. It will help you figure out troubles as you move.
     
  7. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Look at post by nwolfman , similal project.
     
  8. rballard

    Thread Starter New Member

    Aug 3, 2009
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    I did a search on "nwolfman" but only found your message above. Any advice on how to find it?

    Russell
     
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    On tytle bar with All About Circuits, to upper right is a white box with Find next to it. Fill in nwolfman ,hit Find and postings should appear, 'just tried it again to make sure.
     
  10. rballard

    Thread Starter New Member

    Aug 3, 2009
    6
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    Joseph,

    I have been toiling over your #3 diagram for a few days now. While I have learned alot, I have not been able to figure it out. If I understand correctly you have a battery connected that supplies power all the time. The positive is connected to one relay and the negative to the other.

    The diagram shows one wire going in from the 555 timer but the connection goes to both relays, activating each one at the same time. I don't understand that. In addition, my timer has a positive and a negative wire. Where does the negative wire go?

    My knowledge is so limited that this may be more complicated than can be explained through posts like this. If so, my apologies.

    Russell Ballard
     
  11. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    That circuit is a very complex one with electrical more and little electronics.

    If you need to understand it, forget the second poles of both the relays first and try to realize it.

    The 555 is wired as a monostable multivibrator in one shot mode. the LDR is the trigger to start the process. I guess you dont have much experience with the 555, thats why you said both the relays work together. The 555 can produce only one output at a time... either a + or a -. when a positive output comes, the lower relay gets a + and a - and the relay will run whereas the upper relay gets 2 +'s and no GND for it to operate. Forget the motor section, i will explain it later. then one relay will operate and the motor will turn in one direction till it hits the limit switch which opens the circuit and stops everything temporarily. Then it will have to wait till the 555 will provide the opposite pulse and pull the motor in the opposite direction and close the switch, but again the motor reaches the other end and hits the other limit switch and again stops everything. I hope you understood what all I said till now. The method of 'killing' itself can be xplained using this figure below. Understand it well, then you will have an idea.

    [​IMG]

    Next controlling the motor is done with the other 2 poles of the 2 relays. Did you understand my second diagram in the previous post?? That principle is applied to provide (+) & (-) to the motor as well as (-) & (+) to run in opposite directions. When both relays dont work, the motor will get (+) & (+) which is not able to run the motor.
     
  12. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
    141
    Here's a sketch I made of how I'd like to operate a DC motor I have connected up for opening and closing a chicken coop door. I couldn't find a wall wart that put out enough current to run the motor I have nor did I have a transformer suitable for making my own power supply. I'm instead looking for a 120 VDC gear motor. But I'll use substantially the same control circuitry (along with a simple synchronous motor AC timer and a 120 VAC relay; I already have both). I decided to run 120 VAC out to the coop from the house, as battery operation isn't a viable option because we can get sub 0 °F temperatures here during the winter.
     
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