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12 volt regulation help needed

Discussion in 'Electronic Basics' started by bobg, Mar 15, 2005.

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  1. bobg

    bobg Guest

    I have built a very simple PWM controller to control the temperature of the
    grip heaters on a ATV. Uses a 4093 with a transistor, 2 diodes, 2 caps, 1
    resistor and a pot.Circuit is powered by the battery and works ok but the
    temperature increases or decreases slightly with the RPM of the motor and
    the output of the alternator. My question is what is the easiest way to have
    regulated 12.50 volt to power the circuit? The alternator will output 15
    volt max. and the circuit handles 3 amps. max.. Thanks in advance, BobG.
     
  2. John Fields

    John Fields Guest

    ---
    You don't need regulated 12.5V. If you want to keep the grip heaters
    at a constant temperature you need to make that temperature happen
    with the lowest system voltage you've got and then use your PWM
    circuit to keep them from getting hotter as your system voltage
    increases.
     
  3. mike

    mike Guest

    There's a technique used on older bikes.
    Run the heaters off AC, directly off the alternator coils.. Put a
    series inductor.
    As the RPM increases and the frequency increases, the inductor
    has greater impedance.
    When you do the math, you might find that the inductor is physically
    too big for your liking, but it's worth a calculation. YMMV.
    mike

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  4. Expanding upon John's comments (with which I concur), the PWM
    generating circuit you have can probably be simply modified to alter
    the duty cycle in the appropriate direction as the supply changes.
    Showing your circuit, (perhaps with the help of the tool at
    http://www.tech-chat.de/aacircuit.html
    ) would allow folks here to suggest those changes. For a narrow
    range of supply variation, such as can be expected for a vehicle
    battery most of the time, this correction can be close to enough
    to ideal to yield all the improvement you can perceive. (I assume
    the "grips" are something you hang onto and they are heated to
    keep people's hands from getting too cold.)

    What puzzles me is why, if your controller controls temperature,
    is it sensitive to supply voltage at all? That may be due to a
    simple design oversight which can be spotted readily once you
    show the circuit. Alternatively, it will allow others to discern
    which parts could be powered by a low power regulator to fix
    the problem, rather than regulating the power circuit.
     
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