dc variable voltage reduction

Discussion in 'General Electronics Chat' started by chrisvanbekkum, Apr 6, 2009.

  1. chrisvanbekkum

    Thread Starter New Member

    Apr 6, 2009
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    0
    Hi , new to this forum but have hopes somone will be able to help me with a problem. Recently i installed a diesel engine in a gas car . no problem other than the speedometer reading is being way hi . the problem: the dc generator on the transmission output shaft is making more revolutions than before (with the old engine ) and naturally , the speedometer reads hi. from what i can find , the transmission dc generator puts out from 4 to 20 v dc that drives the speedo head and needle. i tried to reduce the voltage to the head by installing a 25 k (max) variable resistor in line but this did not have any significant effect. How can i reduce the voltage by approx 30% that gets to the needle?
    thanks for any suggestions.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Are you certain it is voltage and not frequency that makes the signal?
     
  3. chrisvanbekkum

    Thread Starter New Member

    Apr 6, 2009
    3
    0
    the problem is , i do not know exactly how the generator makes the needle move but think it is by magnetic force , more juice ,stronger pull and higher speed reading
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    It's pretty significant to determine the nature of the signal. Frequency is much less variable than a voltage output.
     
  5. chrisvanbekkum

    Thread Starter New Member

    Apr 6, 2009
    3
    0
    you are right , after doing some more digging , it appears that is is the PULSE frequency that makes the needle move ,not the voltage . is there any way to adjust the pulse ?? if not i may have to invent a gear reduction to slow the generator down.
     
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