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[Q] basic electronics: Batteries

Discussion in 'Electronic Basics' started by [email protected], Sep 2, 2005.

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  1. Guest

    Hi all,

    I have a couple of basic questions on batteries. I only know very
    little about electronics, electricity, so please bare with me for the
    silly questions.

    There AA, D, C batteries in the market (Duracell, etc). Does anyone
    know what amphare (current) for these batteries give?

    If I have 1.5V AA battery, and for an example, it gives 50mA. (I have
    no idea if it gives 50mA.) If a circuit needs 1.5V, but 100mA, what do
    I need to do?

  2. I haven't gotten dressed, yet, but I will try to help.
    Batteries are rated for some product of current and time, usually the
    small ones use units of milliampere hours. Peak current possible is
    usually thought of as short circuit current, but you get no voltage
    under that condition. The short circuit current is the unloaded
    voltage divided by the internal resistance. Smaller cells have higher
    internal resistance. A practical maximum current would include a spec
    for how low the cell voltage can sag (how much of the available
    voltage is consumed as the current passes through the internal series
    That question might be better stated, "I have a 1.5V (no load) AA
    battery, and for an example, it gives 50mA. with the voltage sagging
    to no lower than 1.25 volts for an hour. If a circuit needs at least
    1.25V, but 100mA for an hour, what do I need to do?" The answer is
    that you either need to parallel 2 or more of these AA cells (not a
    good idea unless you are sure all are equally fresh and from the same
    batch) or you change to a larger size cell that has at least twice the
    volume and half the internal resistance.

    Here is a web page that lists some independent test results for
    various cells and batteries:
    Does this data make sense in light of my explanation?
  3. BobG

    BobG Guest

    Since he doesnt know much about electricity, maybe the water analogy
    would help. Volts is like pressure, current is like gallons per minute,
    and resistance is like the size of the hose. Also ohms law is fairly
    simple.... E=IR... volts=current*ohms and Watts=volts*amps. That much
    and some algebra will get you right up there with the engineers with
    batchelors degrees.
  4. WK2

    WK2 Guest

    Thanks. Bear with me next time. ;-)
  5. Bob Monsen

    Bob Monsen Guest

    AA batteries can give peak current of 10A or more. However, if you do that
    you will quickly exhaust them. The capacity of batteries is usually
    measured in 'amp hours' (or milli-amp hours). For example, assume your AA
    cell is 1000 milliamp-hour. That means that if you draw 1A for 1
    hour, or 100mA for 10 hours, or 10mA for 100 hours, you will exhaust the
    battery. Unfortunately, the rate at which charge is pulled out (the
    current) affects the actual amount of charge you can get. Generally, the
    more current, the less total charge can be obtained.

    Current also affects the voltage, since the battery can be thought of as
    a resistor in series with a voltage source. As a cell discharges, it's
    internal resistance increases. Thus, it's voltage goes down...
    example, it gives 50mA. (I have no
    There are different kinds of AA cells. Alkaline cells are the main kind of
    'primary' cell, which basically means non-rechargeable. "secondary" cells
    are rechargeable, and come in various tasty flavors, like nicad, nimh,
    liion, etc. nicad and nimh cells are both 1.2 volts nominal, whereas liion
    cells are 4.2V. They come in different 'capacities', amp hours. So, you
    can get a 1700 mAH nimh cell, or a 3000mAH nimh cell. They are both 1.2V,
    but one will last longer given a particular current requirement. Some
    cells are also constructed to have different maximum current capabilites.
    For RC aircraft use, for example, you want to have high max current,
    because the electric motors take large currents. For a tape player, you
    may only want 100mA, so a battery that lasts longer, but doesn't allow
    larger max currents can be used.

    You can find out more by going to the duracell site, and looking at the
    battery specifications.

    Look here:

    Bob Monsen

    If a little knowledge is dangerous, where is the man who has
    so much as to be out of danger?
    Thomas Henry Huxley, 1877
  6. redbelly

    redbelly Guest

    And those voltages are not fixed numbers either. A freshly charged
    NiMH cell has about 1.4 to 1.5 V, which slowly drops during use.
    I've measured close to 3.2 V on brand new "3V" lithium coin cells.

  7. Bill Gray

    Bill Gray Guest

    So a bare bear would be furless?

  8. The appropriate question is, will he help you bear your burden?
  9. Jasen Betts

    Jasen Betts Guest

    look at the lamps used in torches (US:flashlights) an AA powered torch will
    typically have globe that uses upto 500 mA etc...

    from a list in a catalogue I get the following

    AA 500mA
    C 600mA
    D 750mA

    these figuures depend somewhat on the batteries involved,
    AA size NiCd cells can produce 2 or 3 amps quite readily, but it's nore real
    good fo them...

    unfortunately the makes of primary (non rechargable) baatteries don't seem to
    publish their technical specifications...

    at 500mA an AA cell isn't going to last real long (hours?)

  10. John Fields

    John Fields Guest

  11. John Fields

    John Fields Guest

  12. At 0.5A your typical AA alkaline battery will be dead well before the 3
    hour mark.

    *Motors: NiCd, non-rechargeable lithium's, alkaline's.
    *Moderate ~ High drain solid state devices: Li-ion and NiMH
    *Low drain devices: Any type, rechargeable Li-ion and NiMH cells should
    not be used with simple, analog, resistive loads such as lamps and
    motors because they can potentially damage the cell if you let the
    device completely drain it, not good for NiMH cells.
    *Flashlights, smoke alarms, pocket radios, TV remote controls: Alkaline
    or other non-rechargeables that have a *long* shelf life. All batteries
    self discharge but rechargeable batteries have a very high self
    discharge rate, NiMH's have the highest self discharge rate at around
    1% per day, logarithmic decay. This self discharge can be slowed by
    storing batteries in the fridge, but not the freezer!

    Rechargeable lithium ion cells work at 3 ~ 3.6V, so, you won't find
    them in AAA, AA, C, or D format because those are all 1.2 ~ 1.6V cell
    formats, the next best thing to Li-ion's are nickel metal hydride
    (NiMH) cells. These things are perfect for today's high drain digital
    devices because... well, this guy puts it in better words then I can: Also they have no "memory
    effect" and with a good smart, "microprocessor controlled", charger the
    batteries can last 500 - 1000 charge/discharge cycles.

    Also check out this site, pay attention to the "Watt-hours" column in
    the battery table and note that the Alkaline cells are all the way at
    the bottom:

    and you can lookup data sheets here: and buy
    NiMH/NiCd stuff here:
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