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Momentary Switch to directional DC motor

Discussion in 'General Electronics Discussion' started by Halcyon, Dec 26, 2019.

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  1. Halcyon

    Halcyon

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    Dec 26, 2019
    I have an application that involves a 12V/24Vdc motor that currently uses a momentary toggle switch to tilt forward and back, depending on the direction the switch is pushed.
    I need to switch the toggle to a momentary PushButton. Each time the PB is pushed, the motor alternates direction- only while the button is held down.
    Many thanks in advanced!
     
  2. Martaine2005

    Martaine2005

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    May 12, 2015
    As you already have a two way toggle switch, that suggests a physical switching of polarity.
    A momentary push button switch is either push to close or push to open. Without any more information of your wiring setup it’s hard to say. I would think by your basic description that extra circuitry via relays or H bridge would be required. In order for anybody to make suggestions, you will need to be more specific.
    Is your ‘momentary toggle’ latching? ie- does it stay in the direction pushed until direction is changed?.
    What kind of motor?. What current does it draw?. Etc.

    Martin
     
    Bluejets likes this.
  3. Bluejets

    Bluejets

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    Oct 5, 2014
    Another consideration is that at power up, one or the other directions needs to be set prior to the switching.
    Several flip-flop arrangements immediately come to mind but whichever way you go, it is going to become a LOT more complex than that which you already have.
     
    Martaine2005 likes this.
  4. Minder

    Minder

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    Apr 24, 2015
    I have a flip-flop circuit made up of a couple of 24vdc relays, but the relays are maintained alternately.
    You could however add a N/O section to the sw ( DPST-PB) which should do the trick for you.
    M.
     
  5. Halcyon

    Halcyon

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    Dec 26, 2019
    Hi Martin
    The current toggle switch is non latching. It’s ON-OFF—ON, the motor moves forward only while the switch is held in a direction.
    I will get my hands on the motor next week, but my suspicion is that it’s 5-10Amp. I hope that helps.
     
  6. Halcyon

    Halcyon

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    Dec 26, 2019
    Hey Bluejet
    The complexity difference is anticipated.
    At power up, what will be the state of the motor (spinning or idle?) if we preset the direction.
     
  7. Minder

    Minder

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    Apr 24, 2015
    Your required description in the OP states you would like to use a PB in place of the toggle?
    This circuit would only need the addition of a N.O. section on the PB and wired in series with motor power.
    Using the first diag. you could just include 2 of the unused relay contacts for motor polarity switching
    M.
     

    Attached Files:

    Last edited: Dec 26, 2019
  8. Halcyon

    Halcyon

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    Dec 26, 2019
    Hey Minder
    I will try this and update you.
    Many thanks!
     
  9. Bluejets

    Bluejets

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    Oct 5, 2014
    Beats me how you would know this without knowing which way to go initially.
     
  10. AnalogKid

    AnalogKid

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    Jun 10, 2015
    This can be done with a single DPDT impulse relay and a momentary switch that can handle the motor current.

    ak
     
  11. Halcyon

    Halcyon

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    Dec 26, 2019
    Would you have a cct diagram I can wrap my head around?
    Thanks!
     
  12. Halcyon

    Halcyon

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    0
    Dec 26, 2019
    Just to clarify
    Is a 3rd Relay required (RLC), or is the right side connected to the 2 unused RLA contacts?
    And please clarify what the “Motor Power” terminals connect to? The 24V battery?
    Thanks!
    0C495659-AEAE-4B93-BC7A-C68C7A9036F0.jpeg
     
  13. Audioguru

    Audioguru

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    Sep 24, 2016
    Here is a very simple "alternate action" circuit. Push the button and the output goes low. Push the button again and the output goes high. Push it again and the output goes low again, over and over if you want.
    this circuit can control a power h-bridge that drives the motor forwards or reverse.
     

    Attached Files:

  14. Halcyon

    Halcyon

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    Dec 26, 2019
    Would this be a monetary action- motor activated only while PushButton is pressed?
    Thanks!
     
  15. Audioguru

    Audioguru

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    Sep 24, 2016
    The "alternate action" circuit I posted is a simple flip-flop. The pushbutton only changes the forwards or reverse direction of the motor that runs continuously.
     
  16. Minder

    Minder

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    Apr 24, 2015
    The return is shown as two places where the GND or common connection is made to the DC supply common.
    With the logic circuits you still need a reversing relay or?
    Using the first flip-flop relay cct, (flipflop.pdf) you use a spare contacts on RLA for fwd/rev.
    Using just 24vdc.
    M.
     
  17. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Not until next Monday or Tuesday. I'm traveling and can't do schematics on this device. What you want are a reversing function (like a DPDT relay) and a toggle flipflop function. A bistable impulse relay can do both:

    https://www.te.com/commerce/Documen...m=1308242_S89RS90R&DocType=DS&DocLang=English

    The + DC input goes to one relay pole and one coil pin. The other relay pole and the other coil pin go to one SPST switch contact. The other switch contact goes to DC-. In this way, closing the switch sends current through the relay contacts to the motor *and* energizes the relay coil. Every time the coil activates, the relay toggles the contacts to the other DC polarity out to the motor.

    ak
     
  18. Minder

    Minder

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    Apr 24, 2015
    A problem here may be in attempting to instantly reverse the motor, if running in high speed in each case, could stress motor and P.S.!
    Effectively creating a dead short until motor actually reverses.
    M.
     
  19. Minder

    Minder

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    Apr 24, 2015
    The DPST P.B. will assure the motors off between each push.
    M.
     
  20. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Here is a first pass at the approach I described above.

    Notes:

    1. 100% of the motor startup and running currents go through the switch. The switch contacts should be rated for at least twice the motor startup current value. If this is a problem, then a smaller switch can drive a SPST relay.

    2. There will be a very short (a few milliseconds) current pulse to the motor in the wrong direction before the relay changes state. Most motors cannot start moving in that short a time, so it should not be a problem.

    3. D1 clips the back-emf spikes from both the motor and the relay coil. Depending on the size of the motor, it might need to be larger.

    ak
    MotorReverse-PB-1-c.gif
     
    Last edited: Dec 30, 2019
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