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What does a battery tester measure?

Discussion in 'Electrical Engineering' started by Just A Guy, Jun 1, 2008.

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  1. Just A Guy

    Just A Guy Guest

  2. Roy

    Roy Guest

    It's a tiny D'Arsonval Movement meter that measures Bad or Good and a
    mark for Low for batteries power...
    It works with the voltage in the cells you test, since you place it
    between + & - post of the battery., just about anything under 1vdc will
    be in the red zone.........

    Roy Q.T. ~ US/NCU ~ E.E. Technician
    [have tools, will travel]
     
  3. Palindrome

    Palindrome Guest

    The key thing is what it is not - a simple voltmeter measuring the
    off-load voltage produced by the cell.

    These testers have a built-in load resistor and give an indication of
    the voltage that the cell will produce when powering equipment.

    Some testers (not this one) draw a great deal of current when used -
    testing too often and for too long can substantially reduce battery life!

    Radio Shack do have a web page that discusses testing batteries:

    http://support.radioshack.com/support_tutorials/batteries/batgd-B08.htm

    Which only shows why you shouldn't go to Radio Shack for technical advice ;)
     
  4. Roy

    Roy Guest

    Hi Sue ` as usual you're right...I don't think he read that RS link page
    on batteries or he wouldn't have had to ask }:

    http://support.radioshack.com/support_tutorials/batteries/batgd-B08.htm

    I doubt he bought it there at all};
    I have one just like it that gets stuck when a fresh battery is tested
    and I have to tap it to get it to rest again };) a nice lady
    exhibitionist or is it exhibitor};)well., I got it @ a battery expo in a
    trade show.
    [they're pretty handy testing cups full of stashed battries]

    Roy Q.T. ~ US/NCU ~ E.E. Technician
    [have tools, will travel]
     
  5. Just A Guy

    Just A Guy Guest

    Roy said
    I did not, but I have now read it, and it did not help. My goal is a
    better understanding of the mysterious world around me, with the hope
    that through a more "accurate" model of reality, I will be better
    equipped to predict and control my environment.

    Or, in more practical terms, for about 2 years I have owned a Kodak
    digital camera. In reviews of this camera in sites such as Amazon.com,
    owners often complain about the difficulty of finding batteries which
    will make this camera work. I've been using a variety of different
    brands of NiMH batteries. Lately, some batteries which worked fine
    before will not now operate the camera, although all these batteries
    grade similarly in the RS battery tester, and all will operate an FM
    radio.

    So I'm trying to figure out what's going on. What is it about this
    camera that is so fussy about batteries? Why are these batteries
    starting to lose their uumph? Is there a different sort of meter that
    will more accurately predict whether a battery will work my camera? Why
    do they all test good in the RS tester?
    Doubt not; I did.
     
  6. Palindrome

    Palindrome Guest

    The problem is that digital cameras tend to both draw a high current and
    need a high voltage from the battery, at the same time. Your tester
    almost certainly is not drawing a high enough current to give a
    realistic reading of what the voltage will drop to when in the camera.

    Different cells, from different manufacturers, of different ages, at
    different temperatures, of different mAH rating, will perform
    differently under the camera load - but will look to be doing much the
    same on the tester as it is at the moment.

    The answer is to modify the tester so that it does draw the same
    current, when testing, as the camera does when running. Which will mean
    adding an additional resistor between the two test terminals of the tester.

    I happen to have a new camera here with new freshly recharged batteries,
    (intended as a gift for someone). So I measured the current to see what
    sort of current is drawn. This one, with 4 cells, draws 0.5A.

    The nearest preferred value resistor as a dummy load to test individual
    cells would be 2.2 ohms in my case. You would probably need something
    similar, but you could measure the current that your camera takes and
    adjust the value to suit, if necessary.

    A modified tester should show you a significant difference between the
    readings of "good" and "bad" batteries, for your purpose.

    Note that the "bad" batteries will still be good enough for many, many
    applications that aren't as demanding in current and voltage as a
    digital camera.
     


  7. If you find out, please let me know. I'm in a similar situation with my
    DC 240.
     
  8. krw

    krw Guest

    Volts, under some load.
     
  9. Roy

    Roy Guest

    Sun, Jun 1, 2008, 6:39pm (EDT+4)
    From: (Palindrome)
    Just A Guy wrote:
    Roy said
    I don´t think he read that RS
    link page on batteries or
    he wouldn´t have had to ask

    I did not, but I have now read it, and it did not help. My goal is a
    better understanding of the mysterious world around me, with the hope
    that through a more "accurate" model of reality, I will be better
    equipped to predict and control my environment.
    Or, in more practical terms, for about 2 years I have owned a Kodak
    digital camera. In reviews of this camera in sites such as Amazon.com,
    owners often complain about the difficulty of finding batteries which
    will make this camera work. I've been using a variety of different
    brands of NiMH batteries. Lately, some batteries which worked fine
    before will not now operate the camera, although all these batteries
    grade similarly in the RS battery tester, and all will operate an FM
    radio.
    So I'm trying to figure out what's going on. What is it about this
    camera that is so fussy about batteries? Why are these batteries
    starting to lose their uumph? Is there a different sort of meter that
    will more accurately predict whether a battery will work my camera? Why
    do they all test good in the RS tester?

    The problem is that digital cameras tend to both draw a high current and
    need a high voltage from the battery, at the same time. Your tester
    almost certainly is not drawing a high enough current to give a
    realistic reading of what the voltage will drop to when in the camera.
    Different cells, from different manufacturers, of different ages, at
    different temperatures, of different mAH rating, will perform
    differently under the camera load - but will look to be doing much the
    same on the tester as it is at the moment.
    The answer is to modify the tester so that it does draw the same
    current, when testing, as the camera does when running. Which will mean
    adding an additional resistor between the two test terminals of the
    tester.
    I happen to have a new camera here with new freshly recharged batteries,
    (intended as a gift for someone). So I measured the current to see what
    sort of current is drawn. This one, with 4 cells, draws 0.5A.
    The nearest preferred value resistor as a dummy load to test individual
    cells would be 2.2 ohms in my case. You would probably need something
    similar, but you could measure the current that your camera takes and
    adjust the value to suit, if necessary.
    A modified tester should show you a significant difference between the
    readings of "good" and "bad" batteries, for your purpose.
    Note that the "bad" batteries will still be good enough for many, many
    applications that aren't as demanding in current and voltage as a
    digital camera.
    --
    Sue

    You're not kidding - There are special batteries for digital
    applications - alkaline and other gp batteries fail mimicking dead after
    a few repeated clicks on the battery powered device [cam etc.]

    most batteries repond well to instantaneous repetitous demand on low
    charge devices where the demand is greater & more dependent on voltage
    than on current flow [as in the glow of a grain of wheat lightbulb] -
    but with digital devices the demands is both for current & voltage this
    can cause severe drainage to the cells charge almost instantaneously.,
    leaving the lcd screen on will only affect the chemicalization process
    more that which maintains the charge turns null....

    I always wondered if I [one] could get radioactive waste and make good
    barreries from it but got stopped by how to turn metal waste into
    paste}:)

    The batteries for digital devices/cameras are made up so that the cells
    don't drain on instantaneous repeatitive demand...
    one thought is the individual cells are probably just stacked closer
    together inside the battery and electrons flow through easier....plus,
    "the stuff" inside has to be more lucid:) as with lithium ...

    Roy Q.T. ~ US/NCU ~ E.E. Technician
    [have tools, will travel]
     
  10. The problem may be that the batteries have developed too much internal
    resistance. A digital camera may draw several *amps* from the batteries
    while recharging the flash after a flash photo, and older cameras were
    somewhat demanding on batteries even when the flash was not fired.
    If there's too much internal resistance, the battery voltage will drop
    during flash recharge and the camera will shut down. This is the same
    reason that alkaline batteries tend not to work well in older digital
    cameras.

    Your FM radio receiver probably draws a few thousandths of an amp, so
    internal resistance doesn't matter. Your battery tester will draw
    somewhat more, maybe 50 or 100 mA, but that's still not enough to
    simulate the load a camera places on the batteries.

    Dave
     
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