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Reversing polarity on push of a button

Discussion in 'General Electronics Discussion' started by LightShow, Sep 11, 2018.

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  1. LightShow

    LightShow

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    Jun 9, 2016
    Hey guys..

    im helping a mate repair and restore his 1990 mx5 miata of which he has a motor controlled exhaust valve that opens and closes by swapping polarity, this used to be controlled by a box and a reciever however this box broke and now no longer is available to be used.. at the moment i have the exhaust connected to a dpdt momentary switch however he wants to integrate a single momentary push button to control the opening and closing of the valve..

    basically the need is - a single momentary push button to reverse the polarity of the motor however the circuit must be capable of 15A at 12V and must also not output anything when the button is not pressed

    So basically push button (outputs 12v and GND) release button (No Positive output) Push button (outputs GND and 12v (Reverse Polarity))

    Also Circuit will be installed in a car so it should be capable of up to 14.4V

    Anyone got any ideas??
    Regards, lightshow
     
    Last edited: Sep 11, 2018
  2. AnalogKid

    AnalogKid

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    714
    Jun 10, 2015
    This can be done with a latching DPDT relay (also called an impulse relay) and a SPST momentary switch. The problem is finding parts rated for 20 A DC.

    ak
     
  3. LightShow

    LightShow

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    Jun 9, 2016
    how would that circuit be wired? constant power into the relay as well as the switch then the output off the relay? and are they able to NOT output voltage when no buttons are pressed?
     
  4. LightShow

    LightShow

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    Jun 9, 2016
    and honestly i think it could be run on 10A DC
     
  5. AnalogKid

    AnalogKid

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    Jun 10, 2015
    For long term reliability, contacts should be rated for twice the load they carry.

    ak
     
  6. Externet

    Externet

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    Aug 24, 2009
    The hard part for a momentary DPDT is "must also not output anything when the button is not pressed"
    Doing it with a momentary push switch in series to a DPDT switch is easy.
    And a momentary up/down window switch type has center off, also applicable but has two buttons, if you can live with it.
    ----> https://www.ebay.com/itm/POLARIS-RZ...ash=item3ae6de3207:g:CGcAAOSwXY5ZPxim&vxp=mtr

    Look at wreckyards and for other models/years that such control was implemented by Mazda.
    Try calling
    ----> http://www.car-part.com/
    ----> http://treasurecoastmiata.com/c-370437-used-miata-parts-miata-90-97-electrical-engine-and-body.html
    ----> http://www.planet-miata.com/index.php?section=31630995

    The whole ----> https://www.ebay.com/itm/60mm-Wirel...693787?hash=item3f79d1369b:g:gXwAAOSwAfpatKwD
     
    Last edited: Sep 11, 2018
  7. Alec_t

    Alec_t

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    Jul 7, 2015
    There is also the little matter of should the valve automatically return to the default state (presumably closed) when the ignition is turned off?
     
  8. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Something about my initial reading led me to think he wants the latest state to be latched even when power is off, so the car starts up in the previous state.

    LightShow - ?

    ak
     
  9. hevans1944

    hevans1944 Hop - AC8NS

    4,587
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    Jun 21, 2012
    A mechanically latching DPDT relay with outputs (12 VDC and Ground) in series with DPST N.O. contacts on the push-button switch could work. Problem is, this type of relay generally has two coils which must be energized alternately to change the relay state. How to do this with a single N.O. contact on a push-button switch is problematic. Energy storage capacitors and steering diodes come to mind, but the last time I developed such a circuit was in the 1960s where it was used for a mechanically raster-scanned optics table. The customer needed to preserve the scan direction to allow the scan to resume in the same direction after a power failure. Needless to say, this was waaay before personal computer ICs became available.

    It should be very easy to implement this with a small PIC microprocessor today. Choose one with non-volatile, program-accessable flash memory to preserve valve state after a power interruption. The PIC can drive either real relays with its output, or use power MOSFET switches.
     
    LightShow likes this.
  10. LightShow

    LightShow

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    Jun 9, 2016
    currently as it stands we have it on a momentary on/off/on switch in the dash however the "want" is for a single push button

    It would be nice for it to close when the ignition is off however its not absolutely needed

    Again its sorta eh it doesnt matter too much



    This seems really cool! but unfortunately i have no idea about programming IC's the most ive done is made basic arduino scripts and sent them through an FTDI
     
  11. LightShow

    LightShow

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    Jun 9, 2016
    wants to use this - https://www.adafruit.com/product/558 (or something like it)

    this is what he already has - https://www.avsontheweb.com/momentary-on-off-on-rocker-switch-6-prong/

    the wiring at the moment is like this
    -Dedicated 12v Constant power Run from battery (alot of the wiring is shot in the car so i ran new everything)
    -Dedicated wiring going to the exhaust valve
    -both wires are coming through to the dash where they are wired to the switch in this configuration
    [​IMG] (except its not a window motor and its not a ford xD)

    -system is fused behind the switch with a 15A inline and at the boot with a 50A main fuse for all the new power runs


    The exhaust system is this [​IMG]
    [​IMG]
     
  12. Alec_t

    Alec_t

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    Jul 7, 2015
    If it really must be single-button operated and you don't want to go the micro-controller route, here's the basis for a circuit to do the job :-
    ExhaustValveController.JPG
    The relays are the common automotive type with contacts rated to handle the DC motor current. Depending on the relay coil current draw, N-channel MOSFETS M1-3 could be replaced by BJTs.
    U1a is half of a dual-latch IC and toggles state each time the button is pressed. Its unused inputs should be grounded. M2 enables either relay to be energised, but only when the button is held down.
    The simulation file is attached if anyone wants to play.
     

    Attached Files:

    LightShow likes this.
  13. LightShow

    LightShow

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    Jun 9, 2016
    WOW you went above and beyond! Many many many thanks! What software did you use??
     
  14. Alec_t

    Alec_t

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    Jul 7, 2015
    LTspice (a free download from Analog Devices).
     
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