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convert 12V down to 9V DC

Discussion in 'Electronic Basics' started by [email protected], Oct 3, 2008.

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  1. Guest

    My kids' electric scooter has a 6V motor and battery. The 6V battery
    doesn't give enough juice, but a 12V battery I installed gives too
    much juice (wheels skidding when the pedal is pressed, etc).

    The "Gas" pedal is a simple on/off switch.

    I'd like to provide 9VDC, at about 5A (a guess - I haven't measured
    the current yet - that will take some doing, to determine the startup
    surge current with a kid sitting on it).

    I was thinking LM317 with pass transistor (I've got a spare 2N3055),
    but I'm wondering if I can simplify this schematic a bit (under High
    Current Regulated Supply):

    Why a 2N3904, why so many resistors? Can they be omitted?

    I was also thinking of a buck converter, but I have no P-channel


  2. Jamie

    Jamie Guest

    Just put some large diodes in series, each will give you a ~ 0.6 volt drop./
    The simplest method I can think of."
  3. Tom Biasi

    Tom Biasi Guest

    Controlling large currents like that is always a PITA.
    For cars and scooters I usually make a "shifter" by tapping batteries at 3,
    6 , 9, and 12.

  4. Guest

    Update - surge current is around 15-20 A actually with the 12V
    battery. A linear regulator might not be such a great idea after

  5. Guest

    Interesting; I'll look into that...

    Thanks; I'll look into that. I have a slightly (physically) bigger 6V
    battery that I'll try. (None of them spec their surge current
    capacity, only A-hr capacity... more research needed...)

    Yep, heat... I guess I could be safer by using 20 3V, 1A light bulbs
    to allow 20 A to pass, but then that wouldn't be exactly cheap

    Yep, especially for 20A...


  6. neon


    Oct 21, 2006
    Motors like batteries don't care about volts . use an lm117 as a current regulator with the 2n 3055 pass then just vary the current easy enough.
  7. Guest


    That did it! A fatter 6V battery does the trick.


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