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AA battery discharge rating

Discussion in 'Electronic Design' started by Dutchman, Jul 26, 2007.

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  1. Dutchman

    Dutchman Guest

    I am unclear on how battery manufacturers rate their batteries is it
    over a period of 20 hours?

    How much current can a 1.5V AA Duracell battery provide?

    Thanks!
     
  2. Joerg

    Joerg Guest

  3. Dutchman

    Dutchman Guest

    If I put an additoinal battery in series can I double all the values
    in the datasheet?

    Thanks for the info!

    -Henk
     
  4. Joerg

    Joerg Guest

    The voltage will double but not the current.
     
  5. Joerg

    Joerg Guest

    Correction: I meant the voltage doubles but not the current rating and
    capacity.
     
  6. Eeyore

    Eeyore Guest

  7. Dutchman

    Dutchman Guest

    Thanks guys! I am reviewing everything now! :)

    -Henk
     
  8. LVMarc

    LVMarc Guest

    Dutchman,

    I am working on extending the battery life of prodcut that use "aa"
    alkaline batteries. First is t design circuit with curretn effciency in
    mind, then size alakaline battery, then you add the "soalr green power"
    unit ad extend the battery lifetie significantly!

    Marc
     
  9. Guest

    Buck-boost should be explored. Note that you can run alkaline AA cells
    until they are nearly dead since they are disposable. Most consider
    end of life to be 0.5V, maybe 0.4V depending on the application.

    Without doing the math, I would venture the longest life design would
    be a buck switcher which is designed to work at the 0.5V per cell
    limit. This is often quite a stack of cells. The buck-boost is often
    more practical, but I don't believe it is more efficient.
     
  10. neon

    neon

    1,325
    0
    Oct 21, 2006
    asuming the load remains the same adding one or more battery in series will double the power someone sugested that the current remains the same that is wrong battery can and will provide any current neccessary unfortunately not for long. deep discharge of a battery may destroy the unit whereby the voltage is there without any current capability. a 'D' cell can dliver 2 amps into a short.
     
  11. Dutchman

    Dutchman Guest

    How does Amp hours translate into service hours from the battery
    datasheets?

    I pulled up the datasheet for the Duracell MN1500.

    http://duracell.com/oem/Pdf/new/MN1500_US_CT.pdf

    My system has two AA batteries in it and draws about 1W of power. I
    look at the power curve (page 2) and it shows ~1 Amp Hours followig
    the black cureve. But I want to know the actual run time until it
    hits 0.9V. Better yet I want to know the runtime including two
    batteries at this lower voltage level. (1.8V)

    Thank you for any information!

    -Henk
     
  12. Dutchman

    Dutchman Guest

    Anyone? :)
     
  13. OK then, I'll take a shot.

    1W at 3V is 333mA. I will assume this current is constant with battery
    voltage. (This could be wrong, if your load is constant power the
    current will increase as the battery fails. If the load is constant
    resistance the current will decrease as the battery fails.)

    The first graph on Page 2 shows what you need. The green line (mostly
    hidden under the others) can be used to look up the "service hours",
    until 0.9V, for a particular discharge current. It looks like about 4
    hours. This would be the same for two batteries if I understand you.
     
  14. James Arthur

    James Arthur Guest

    My approach: the "Typical Discharge Characteristics" graph--page 2,
    left, 2nd from the bottom--applies.

    The red line shows 1.8 amp-hours for a constant 0.5 W load (x2 cells =
    1w) discharged to 0.9v per cell at 21 deg. C. This curve has the
    advantage of accounting for impedance effects and varying current
    drains over the cell's life.

    The current at any point in the discharge can be computed as 1/voltage
    indicated by this red curve; piece-wise approximate the graph (a few
    pieces will do) time-integrate until you've used 1.8AH, and you've
    solved for runtime.

    (view in Courier)

    Delivered Avg. Cell Avg.
    Charge Voltage I (amps) t
    ----------- -------- -------- ---------
    0-0.25AH 1.4v 0.357 0.70 hours
    0.25-1.45AH 1.15v 0.434 2.76
    1.45-1.7AH 0.9v 0.556 0.45
    ----
    3.91 hours

    IOW, I get the same as John.


    Cheers,
    James Arthur
     
  15. James Arthur

    James Arthur Guest

    Sorry, that's 1.8AH when discharged to 0.8V. It's 1.7AH for 0.9v
    termination, which I used for calculating, but missed when editing the
    earlier text.

    --James
     
  16. Dutchman

    Dutchman Guest

    My application is constant power! How would the calculations be
    different?
     
  17. James Arthur

    James Arthur Guest

    My calculations are for constant power.

    --James
     
  18. ehsjr

    ehsjr Guest

    Why not build a simple circuit and measure the time it
    takes to discharge the battery to whatever limit you
    have in mind?
    One approach: A comparator driving an opto driving
    an external circuit with a relay. The comparator and
    opto need only a few mA. The relay is powered separately,
    and de-energizes when the limit is reached. The relay
    contacts disconnect your load and the comparator circuit
    from the battery, and another set of contacts interrupts
    power to a clock. I use a similar circuit to load test
    large batteries. It ensures that the battery under test
    is not discharged below the limit. The same idea will
    work for you.

    Ed
     
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