Modify Timer to Control 12v Motor

Discussion in 'The Projects Forum' started by Dan Burfield, Aug 12, 2010.

  1. Dan Burfield

    Thread Starter Member

    Aug 12, 2010
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    I am attempting to use an off the shelf programmable timer to control a 12v motor. The timer is one of those that hooks directly to a hose bib and operates a small motor that opens/closes a built in valve.

    The timer has two wires coming out of it. When it turns on there is a brief 1.5v current and when the programmed time is over the polarity is reversed for a brief -1.5v current (this opens and then closes the valve).

    I would like to have this control my 12v pump but I can't figure out how to have those very short currents turn on and leave on the pump and then turn it off at the end of the program.

    Would a latching relay work? I am at a loss and any help would be greatly appreciated.
     
  2. wannaBinventor

    Member

    Apr 8, 2010
    179
    4
    If you are saying there is just a momentary 1.5 volt pulse and then after a programmed time there is a momentary -1.5 volt pulse I'd consider an SCR to control the pump. See what some of the gurus here have to say first, however.
     
  3. Dan Burfield

    Thread Starter Member

    Aug 12, 2010
    10
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    Ok, an SCR to turn it on but how do I use the reversed 1.5v pulse to turn it back off? My (very limited) understanding is that the current will continue to flow through the SCR and applying another pulse to the gate + or - wont do anything. Is this right?

    Thanks for your help.
     
  4. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    In essense you're just wanting a latch circuit controlled by +1.5V = Logic Level 1 and -1.5V = Logic Level 0 which also serves as the reset for the larch. Kind of a low voltage to deal with but with a capactor and IC setup it shoudln't be hard to convert your existing control signal into +5 and 0 volts.

    Due to an unexpected large (and need it almost instantly) type challenge I was hit with yesterday my thinking capabilities have been sort of blanked out until I solve it, however about anyone else here will be able to work that out with ease.
     
  5. Dan Burfield

    Thread Starter Member

    Aug 12, 2010
    10
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    I am already a bit out of my depth but involving IC's would be way over my head. Isn't there a way to do this with a latching relay?
     
  6. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    If you can find a latching relay with a 1.5v coil, then yes. All you must do is wire it up. Done.

    The relay will latch when it sees the 1.5v pulse (as long as it is longer than the required pulse for latching..~10ms)

    Then It will "un-latch" with the reverse polarity under the same pulse time requirements.
     
  7. Dan Burfield

    Thread Starter Member

    Aug 12, 2010
    10
    0
    I got it working, kinda. I am using a latching relay and it works great until I connect the valve. The motor for the valve shorts out the relay, there is continuity between both poles of the motor. Is this common for all dc motors? Anyway, is there a way to stop the relay from getting "feedback" from the motor?

    Thanks for everyone's help, I am a total newb but learning lots and having fun.


    [​IMG]
     
  8. Dan Burfield

    Thread Starter Member

    Aug 12, 2010
    10
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    Here is a simple diagram of wiring.
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  9. wayneh

    Expert

    Sep 9, 2010
    12,156
    3,063
    Yes, to do work they need to draw current and relatively high amounts, so there will be a low resistance across the poles of a DC motor. It's probably lower than your relay's resistance, so most of the pulse is possibly being absorbed by the motor. Maybe there is not enough pulse for triggering the relay then? When you say "shorts out" the relay, do you just mean it doesn't trip and latch anymore, once the valve motor is connected?

    Short of amplifying the pulse, I'm not sure there is much you can do. Would it be physically possible for the motor to trip a limit switch?
     
  10. soda

    Active Member

    Dec 7, 2008
    174
    13
    I use the same tipe of timer you're talking about here.What i've learned about this timer is that the output will stay high for the time period it's being preset-ted. These valve's usually got a solenoid. All the solenoid do is to open up a small hole inside the valve. The moment the timer turn off the valve, the solenoid closes the hole, there's no air to suck in and a diaframe close down the valve. Take a dmm and set it to dc volts and then take a reading wile the timer is on. If you're be able to get any reading while the timer is on,use the diagram i've uploaded for you. All it did is to latch the relay while the timer is on. The moment the timer turn off, there's no voltage at the input of the relay and the relay will reset.

    On the other hand, i cant see why you need a relay to latch if there's a continuous supply from the timer while it's on. Why don't you just connect a relay to the output of the timer and then connect the pump to the relay?

    I anyway going to upload the diagram so you can see how to latch a relay on it's own.
     
  11. soda

    Active Member

    Dec 7, 2008
    174
    13
    @ Dan burfield

    Sorry, i didn't see the 1,5v output of the timer. I thought I saw 1,5Amp output

    Use this diagram to drive the relay. Just make sure you connect the ov output of the 12v supply or wall ward to the ov output of the timer.
     
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