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NB2L (Li-Ion) battery intrinsics

Discussion in 'Electronic Basics' started by Agricolus, Jan 23, 2006.

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  1. Agricolus

    Agricolus Guest

    Hi people.

    Preparing a trip in a country without electricity, I purchased a series
    of NB2L (equivalent) batteries for my Canon 350D. As I'll have more
    batteries than needed when I return, I would like to recycle them in
    electronics circuits of my design. Something is puzzling me with these
    batteries though:
    a. These Li-Ion batteries have 3 connectors labelled "+", "T" and "-".
    b. The voltage (at full charge) between "+" and "-" is about 8 V
    c. The voltage between "+" and "T" is about 6 V
    d. The voltage between "T" and "-" is 0V !!!!

    I would have expected the voltage measured in d. to be about 2V to
    respect the laws of physics... Thus my questions are:
    1. How can one explain the fact that voltages look inconsistent ?
    2. What could the exact usage of all connectors be (especially the "T")
    ? (Is it a feature of Li-Ion batteries?)
    3. Would it be safe to use only the "+" and "-" in electronic circuits
    ?
    4. Where I could get a detailed description of the batteries internals
    ? (Googling a lot, even for the "offical" Canon NB2L batteries, didn't
    help much.)

    Thanks for any help.
     
  2. Pat

    Pat Guest

  3. Agricolus

    Agricolus Guest

    Hi Pat.

    Thanks for the link; it indirectly pointed me to the information I
    needed.

    Summarizing: the key link is the following:
    http://www.gpbatteries.com.hk/pic/Vcl004.pdf

    The facts seem to be:
    1. The main connectors of the battery are (obviously) "+" and "-".
    2. There is an internal thermistor between "T" and "-" (which is likely
    used by the charger to avoid overheating). The thermistor is in the 10
    kohm range (which I just confirmed with a measurement).
    3. The apparent failure of the laws of physics is simply likely due to
    the internal resistance of my voltmeter (which must hence be in the
    30kohm range... :) ).
    4. For electronics applications, only the "+" and "-" connectors should
    be considered.

    These info seem to be confirmed by a series of postings from Sep 2002
    in the French speaking newsgroup fr.rec.photo.numerique. I will admit
    this is true... and report collapse of expensive equipment is it turns
    out that it was not... ;-)

    Thanks.
     
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