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why 1.2V on rechargeabels

Discussion in 'Electronic Basics' started by pil, Apr 7, 2004.

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  1. pil

    pil Guest

    Why does a rechargeable cell only supply 1.2V and not 1.5V like regular
    cells?
     
  2. Because that's the terminal voltage of that kind of battery technology.

    Ni-Cad and Ni-Mh 1.2V
    Zinc-Carbon and Alkaline 1.5V
    Lead-Acid 2.0V
    Lithium (watch batteries)3.0V
     
  3. John Fields

    John Fields Guest

     
  4. pil

    pil Guest

    The chemistry can be changed to create a voltage of 1.5V. Adding more (or
    stronger) electrolyte will increase the voltage. I doubt the fact that
    someone made the cell and it became 1.2V by coincidence. There must be a
    reason for this standard
     
  5. John Fields

    John Fields Guest

    ---
    Top posting is usually a sign of rude and inconsiderate behavior.
    Please don't top post.

    Adding more electrolyte won't change the voltage. Adding a different
    electrolyte or changing the plate materials will, but there are
    compatibility problems like corrosion of the metals by the electrolyte
    which creep up, rendering some systems useless for some applications.

    There are also economic considerations like if it costs $1 to build a
    1AH 1.5V secondary cell VS 25 cents to build a 1AH 1.2V secondary
    cell, guess what? If you need 6V either buy an extra cheap cell to
    get the battery voltage up to 6V or design your stuff to work on 4.8V
    if you can only fit 4 cells in the box.

    1.2V is not a standard, per se, it's a consequence of the combination
    of metals and electrolyte used and is determined by nature. We just
    found it, that's all.
     
  6. Tim Auton

    Tim Auton Guest

    almost as bad as not trimming your posts lol


    Tim
     
  7. Bob Masta

    Bob Masta Guest

    John:
    I'm no chemist, and certainly no electrochemist, but I had the idea
    that the voltage was determined more-or-less entirely by the
    electrodes, given an "adequate" electrolyte (whatever that may be).
    I seem to recall seeing tables of voltages for electrodes, with no
    mention of electrolyte. Does electrolyte really affect the voltage
    (other than in a pathological case), or is it more related to other
    issues like longevity, current capacity, etc, etc. ??? Thanks!


    Bob Masta
    dqatechATdaqartaDOTcom

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
     
  8. John Fields

    John Fields Guest

    I had thought that the type of electrolyte made a difference, but I
    was wrong in that it's not the electrolyte itself which makes the
    difference but, I believe, its concentration. As I understand it, as
    long as you've got the same concentration of ions capable of giving up
    electrons in a solution of HCl and water as you do with, say, NaOH
    and water, the voltages on the metals will be the same. I think the
    trick is finding a set of metals for the electrodes and an electrolyte
    that won't eat them up when there's no load on the battery...

    Here's a good link:

    http://www.tu-darmstadt.de/fb/ms/student/fs/german/lab/w10/mse10-1.htm

    Bill Beaty also has a nice description of the process somewhere, but I
    lost it... :-(
     
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