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Measure charge during charge??

Discussion in 'Electronic Basics' started by steamer, Feb 10, 2005.

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  1. steamer

    steamer Guest

    --I've been having trouble figuring out how to know when a battery
    is fully charged. That is, sure, I can measure its voltage after
    disconnecting the charger, but how could I do it in series, so to speak,
    *during* the charging process? Dumb guy here..
  2. Guest

    What kind of batteries and charger are we talking about here?
  3. ILYA

    ILYA Guest

    Just wait some time and it will be fully charged.
  4. JeffM

    JeffM Guest

    how to know when a battery is fully charged
    When input current no longer adds to the *charge* of the battery,
    that current starts making the batteries warm.
    Modern battery packs / chargers sense this.
  5. John Fields

    John Fields Guest

    That's not necessarily true. For instance, when a lead-acid battery
    is being charged with a constant voltage current-limited charger (as
    it should be), the amount of current the charger will force into the
    battery will decrease as the battery's voltage increases toward its
    fully charged value, with the result that it will run cooler as it
    gets more and more fully charged.

    I don't think it's true, either, for batteries which are charged with
    a constant current, since what heats a battery up is the power its
    internal resistance is dissipating with current passing through the
    battery. Since the internal resistance of a battery _decreases_ as it
    charges, and since the power the battery dissipates is:

    P = I²R

    Then, for a constant I, as R descreases P (and temperature) must also
  6. Jim Meyer

    Jim Meyer Guest

    Connect the voltmeter in series with the batteries and charger.
  7. John Fields

    John Fields Guest

  8. ILYA

    ILYA Guest

    why ?!
  9. John Fields

    John Fields Guest

  10. Jack// ani

    Jack// ani Guest

    This is something really funny!
  11. tlbs

    tlbs Guest

    Some commercial battery chargers have a switch that "samples" the
    battery voltage by momentarily disconnecting the charging circuit and
    connecting an instrumentation circuit (to measure the voltage).

    To do it manually without disconnecting wires, you could use a DPDT
    switch or a relay to switch between the charger and a voltmeter.

    Depending on the type of battery, voltage is usually the best indicator
    of full charge, or as others have mentioned, temperature can also be
  12. peterken

    peterken Guest

    Tried it by measuring the weight before and after charging ?
    Since charge is put in, the weight will increase, thus the amount of weight
    is a measure for charge...
    Might even build a clever circuit that disconnects leads when the weight is
    enough (eg using a spiral spring or so...)
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