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Discussion in 'The Projects Forum' started by GRUBDIGGER, Nov 24, 2010.

  1. GRUBDIGGER

    Thread Starter New Member

    Nov 24, 2010
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    i came by this site and thought someone here could answer my question. I have this 24 volt system and on one circut i only want 12 volts. How can i do this? Thanks in advance.:)
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    What kind of system is it and what is the required current rating?
     
  3. GRUBDIGGER

    Thread Starter New Member

    Nov 24, 2010
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    THE SYSTEM IS IN MY RACING LAWNMOWER.NORMALY ITS 12V.IVE CHANGED IT TO 24V. THE SATER WORKS GREAT BUT ON THE BENDIX SIDE THE 24V KIKS IT UP SO FAST THAT SOMETIMES IT WONT ENGAGE WITH THE FLYWHEEL. SO ON THAT SIDE OF THE STARTER I NEED TO CUT THE SOLENOID BACK TO 12V.:confused:
     
  4. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Use a resistor (R) in series with the solenoid.

    R=(24-Vsolenoid)/Isolenoid

    Rpower=(Isolenoid^2)*R
     
  5. GRUBDIGGER

    Thread Starter New Member

    Nov 24, 2010
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    The wire on the solenoid goes directly to the keyswitch.do i install the resistor in that wire or the wire that suplys voltage to the key switch?

    I dont want to be a pain but im stupid when it comes to this.
    I can make horsepower,just dont do well with the electrical end. Thanks for all your help.
     
  6. whatsthatsmell

    Active Member

    Oct 9, 2009
    102
    4
    Not having a stable full of racing lawnmowers myself, what is the advantage of using 24v? Are you using the magneto ignition or a CDI?

    Are you using two 12v batteries in series to give you 24v? If so, you could run your starter off one of the 12v batteries.
     
  7. GRUBDIGGER

    Thread Starter New Member

    Nov 24, 2010
    5
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    ITS A MAGNETO IGNITION SYSTEM.THE ENGINE HAS SO MUCH COMPRESSION THAT 12V WONT TURN IT OVER FAST ENOUGH TO START IT.24V(2 12V BATTERIES IN SERIES) TO THE STARTER WINGS IT OVER VERY FAST.HOWEVER,THE SOLENOID SHOOTS UP SO QUICK THAT IT WONT ENGAGE WITH THE RING GEAR ALL THE TIME.

    JUST TO FILL YA IN,I RACE THIS ON A NATIONAL LEVEL.WE ARE REACHING SPEEDS 80+ MPH. THIS IS GRASS ROOTS RACING.:D
    IF YOU OR ANYBODY ON THIS SITE WANT TO CHECK US OUT GO TO WWW.GOLAWNMOWERRACING.COM. ITS OUR NATIONAL SITE.
    THANKS FOR ALL THE INFO AND ILL SPREAD THE WORD ABOUT YOUR SITE.:)
     
  8. whatsthatsmell

    Active Member

    Oct 9, 2009
    102
    4
    Do you have a picture of said starter or a link to find one?
     
  9. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    So what current are you needing? Figure max current.

    Welcome to AAC.
     
  10. whatsthatsmell

    Active Member

    Oct 9, 2009
    102
    4
    I don't think the problem is the solenoid. I believe what is happening is the gears are spinning too rapidly before the solenoid has a chance to engage the teeth with the flywheel. Making the solenoid engage slower will only exacerbate the problem.

    I'm thinking possibly a two starter button solution or at least a short time delay circuit that gives the solenoid a bit of a head start to the flywheel before the motor starts to rotate the gear.

    Another solution may be to engage the starter with 12v and then add the other 12v once the gear is engaged.
     
  11. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    Your feeding 24 volts to a 12V starter??
     
  12. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    You may be better off going back to 12V, and using a battery that is "comfortable" supplying a huge amount of current into a near short, such as an Optima Yellowtop. The internal resistance of Optima batteries is the lowest around, and would definately supply the current to spin your starter.

    If you were previously using "lawnmower sized" 12V batteries, stepping up to an AGM battery will be a world of difference, and not effect the rest of the systems that need 12V.
     
  13. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,013
    1,531
    If your using two 12V batteries just connect your solenoid to one of them instead of both. This is how 24V diesel trucks are wired. the 24V is used just to drive the starter motor, all the other circuits - lights, radio, and engine management, are run from 12V.


    this is what it how it would be wired;
    - battery1 + ------- -battery2 + ------Starter
    I
    I
    solenoid
    (couldn't get the solenoid to stay lined up with the + of battery1, but thats where it goes)
     
  14. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Put the resistor on the wire which connects the solenoid and the keyswitch.
     
  15. GRUBDIGGER

    Thread Starter New Member

    Nov 24, 2010
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    Thanks for all the help.problem solved. I ran off of 1 battery for the 12v on the start wire.didnt work so great because of a voltage drop.added a relay and now i have a full 12v. Works fine now.

    This is a wonderful site.thank you all.
     
  16. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    Why didn't you replace the wire that had the excessive voltage drop? Did you inspect the wire to ensure the connections were ok ... including the conection of the wire itself to the connector?
     
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