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wide range DC to 13.8V DC converter

Discussion in 'Electronic Design' started by chris, Nov 30, 2007.

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  1. chris

    chris Guest

    Hi,

    I am trying to figure out how I can make a regulator for a small wind
    turbine. The output is to charge 12V lead acid batteries.

    The turbine outputs from 0-110V - (usually around 20-30V). The normal
    approach is to regulate to 13.8V, and dump the excess voltage through
    a shunt resistor. However this seems very wasteful, and I was
    wondering if there is a way of converting the excess voltage to
    current?

    A long winded way would be to convert the input to a simple square
    wave, and pass it through one of set of transformers, which is
    automaticaly selected based on the input voltage. So T1 could deal
    with voltages 20-30V, T2 30-50V, T3 50-80V... Then rectify and
    regulate the output to 13.8V. As I say, long winded! And there has to
    be a better way!

    Ideas?
     
  2. John Larkin

    John Larkin Guest

    You need a buck switching regulator, which would convert available
    power to battery charging power at ballpark 90% efficiency.

    How much power (in watts) does the turbine generate? How much current
    can the battery stand?

    There may be a standard module available that does what you want.
    Vicor? It's not exactly a beginner's project to design a good,
    efficient, wide-range, current-limited buck switcher.

    John
     
  3. PeterD

    PeterD Guest

    Switching regulator?
     
  4. How much current can the turbine output? or whats its power rating?
     
  5. David Lesher

    David Lesher Guest

    meci.com had a bunch of DC-DC convertors....
     
  6. Nobody

    Nobody Guest

    Buck converter.

    http://en.wikipedia.org/wiki/Buck_converter

    Assuming that the current/power are relatively low (otherwise the
    shunt resistor approach wouldn't be realistic), and you don't need
    particularly high efficiency (it couldn't be any worse than a shunt
    resistor), this isn't that hard.

    You can get dedicated chips which will do most of the work (search for
    "switching regulator"), but at low power you could probably get away with
    just using an op-amp wired as an inverting comparator with some
    hysteresis: if the output voltage is too low, turn the switch on, if it's
    too high, turn it off.
     
  7. chris

    chris Guest

    Thanks for the info.

    The turbine is rated at 100W, and can deliver around 8A. But I would
    rather over-spec anything I connect to it as in high winds it may
    output more.

    If modules are available, I could presumably connect several in
    parallel to achieve the current handling?
     
  8. foobar

    foobar Guest

    I have thought about this problem before.

    It is a complex load matching problem. The electrical load that the
    turbine feels will directly effect the mechanical resistance of the
    turbine. But for any given wind speed there is an optimal rotation speed
    to deliver max power. That is, as the wind speed goes up, you can ratchet
    up the resistance on the turbine. But if you ratchet it up to high, too
    soon, the turbine will enter into an inefficient aerodynamic region, and
    no longer deliver loads of power.

    Furthermore, depending on the state of the battery, there is a max
    power it can accept (going down to near zero when the battery is fully
    charged). In case the turbine is delivering more electrical power than the
    battery can accept, you need to dump that power into some kind of heating
    device (resistor or transistor load).

    If you have something that works already, and was designed by
    professionals, I would not try to improve on it.

    --Mac
     
  9. JosephKK

    JosephKK Guest

    chris posted to sci.electronics.design:
    Probably not, unless they were specified to do that.
     
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