Help need to delay a relay

Discussion in 'The Projects Forum' started by ihfarmer, Feb 2, 2014.

  1. ihfarmer

    Thread Starter New Member

    Feb 2, 2014
    3
    0
    So I bought this really cheap rc car just to tinker with. I took the motor off the original circuit and made a new on that is triggered by the original circuit, so now the motor is ran on 18v instead of 6. I want to engage one 9 volt then automatically engage another 9 volt battery, because 18 volts is too much take off power for that car so I want to stair step its power. Any ideas how this can be done? thanks!
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    The best way is a Pulse Width Modulator (PWM). A dual opamp, one section as an integrator to create the speed-up ramp; the other as a comparator to create the varying PWM. A power FET as the PWM switch.
     
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  3. ihfarmer

    Thread Starter New Member

    Feb 2, 2014
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    Are both of those things something I can get at radio shack?
     
  4. inwo

    Well-Known Member

    Nov 7, 2013
    2,435
    315
    A cheap and dirty fix is a relay and capacitor across the coil.

    Find a tiny 9 or possibly 12 vdc relay. Highest ohms coil the better.

    Connect a 2,000uf or so across the coil.
    Feed coil from whatever powers motor circuit, thru the largest value resistor that will pull it in. 100 ohms or so. To the coil/cap. combo.

    Connect the 2-9v in series as you have.

    Leave the negative (common) side connected to (-)motor as is.

    Connect the +9 volt lead (from center tap) to the NC of relay.
    Connect the +18 volt lead to the NO of relay.

    Connect (+)motor lead to relay common.

    When powering circuit motor will be on 9v.
    After cap charges and pulls in, relay will switch motor to 18v.
     
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  5. ihfarmer

    Thread Starter New Member

    Feb 2, 2014
    3
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    Thats what i might do sounds simple enough cause I don't have that good of understanding of how PMW's or FET's work.
     
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