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Thread: Pre-rotator using 12 volt Car Starter with slow start using 24 volts for high speed

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    PRA Secretary JOHN ROUNTREE 41449's Avatar
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    Pre-rotator using 12 volt Car Starter with slow start using 24 volts for high speed

    We are still working on the bushless motor solution but as asked to post a drawing of my other idea using a Car starter motor.

    Basically it has a Pre-rotator off/on switch with a 3 position speed selector switch.
    Procedures for use:
    1) Turn the 3 position switch to #1 = slow start.
    2) Turn on the pre-rotator toggle switch and wait for it to hit max slow start speed.
    3) Turn the 3 position switch to #2 = 12 volt mid speed and wait for it to hit max speed.
    4) Turn the 3 position switch to #3 = 24 volts high speed and wait for it to hit max speed.

    5) Turn off the toggle off/on switch when it hit max high speed.

    If it were me I would mount the starter motor near the CG and use a shaft or Tommy's flex cable to drive it from there.

    Also you could add a 6 volt battery instead of 12 volt and make it 18 volt.

    The only downside I just realized with this schematic you cannot charge the 2nd battery while flying. But you would only have to isolate the two batteries from the pre-rotator circuit with one more solenoid to make that happen.

    I have not done it yet! But now that this PM reminded me of it I will ask Bruce if he would like to try it on his little wing.

    I know you can run 24 volts at least through a Mercedes Benz 300D starter for years without burning it up and that is where this theory was born.

    Here is how I know: (This is copied from the PM of a post I posted on another thread years ago)

    Years ago we had an airport courtesy car.

    It was a Mercedes Benz 300D (IIRC) but had over 750,000 miles on it when we started using it as a courtesy car.

    Shortly after placing it in service it started having problem starting when cold having such low compression and being a diesel.

    My brothers solution was install a second battery in series and running 24 volts through a 12 volt starter.

    This turned her over TWICE as fast and she always started right away from then on.
    To our surprise, we got another 50,000++ miles out her and the engine blew up before the original starter motor burnt out = several years latter.

    Based on my experience with my brother's solution for the airport courtesy car this should work for years.
    Attached Thumbnails Attached Thumbnails PreRotatorSchmatic2.jpg  
    Last edited by JOHN ROUNTREE 41449; 06-24-2016 at 11:23 PM.
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