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Voltage of In-car charger for MP3 player

Discussion in 'Electronic Basics' started by [email protected], Jan 21, 2006.

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  1. Guest

    I have an MP3 player and the mains charger delivers 5V, 2.4A. The
    manufacturer's "proper" in-car charger has the following specification:
    Input 12V - 24V DC, Output 5V 2.5A . I recently picked up an in-car
    charger (cigarette-lighter socket thingy) which can do multiple
    voltages ... except 5V of course. It does 4.5V and it does 6V - am I
    going to damage anything by trying to charge or run the MP3 player off
    either of these voltages? If not, which one should I use? Also, how
    do I determine which polarity to switch the charger to?

    Many thanks in advance for any help,
  2. Rich Webb

    Rich Webb Guest

    A direct approach to "which charger" would be to measure the actual
    current and voltage delivered by the manufacturer's charger to the mp3
    player under varying load conditions (idle, in use, flashing lights,
    whatever it does). Then make a resistive dummy load that gives the same
    current/voltage results with the real charger attached to it and test
    the multiple output wall-wart to see which setting is closest in voltage
    for the required current draw.

    Somewhat more approximately: multiple output wall-warts are generally
    not very "stiff." Under light load conditions, the 4.5 V may really be 6
    V or more and the 6 V out, closer to 8 or 9 V. Think of the 4.5 V as
    "about 5 V for light loads" and the 6 V as "about 5 V for heavy loads."

    Assuming that the multiple-output wart is rated for at least 2.5 A, I'd
    start with the 4.5 V setting and see how it goes. Probably (but no
    guarantees) that will work. If not, bump it up to 6.

    Without having measured the actual performance of the manufacturer's
    device and also the wart, either alternate setting does carry a slight
    risk, perhaps of not a high enough voltage for the mp3's regulator or of
    too high a voltage, forcing it to dump excess as heat and possibly
    damaging the player.

    As to which polarity, the manufacturer's charger or the mp3 player
    should have a diagram like +-Co-- or --Co-+ to indicate what's required.
    To be sure, go to your closest Radio Shack and get one of their
    autoranging pocket multimeters and measure it. They're pretty cheap and
    they do come in handy ...
  3. Pooh Bear

    Pooh Bear Guest

    Those cheap chargers often have poor voltage regulation. I wouldn't chance
    using one unless I knew *exactly* the likely consequences.

    Polarity can be easily determined with a meter btw.

  4. Jasen Betts

    Jasen Betts Guest

    measure the output of the provided charger. if it's exactly 5v using other
    than 5v could cause problems.
  5. ehsjr

    ehsjr Guest

    If the in-car charger you have truly puts out 6 volts
    at at least 2.5 amps, you can put a 1N5401 diode in
    series with it and the MP3. That will deliver ~5.3 volts
    under load. You will need to determine the polarity of
    things - use your meter to determine which is + and -.

    If you have doubts about the in-car charger, forget
    the whole thing.

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