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What is the difference between D and AA batteries?

  1. Jan 10, 2014 #1
    ehow explains there is more current (see below). But suppose there is a simple circuit which includes a flashlight bulb and one battery. The voltage of each battery is = 1.5V and because we are using the same bulb in the above circuit, the current should be the same. Is ehow correct?

    Battery size determines the amount of current available. The D cell batteries give more current than the C cell batteries, and the AA cell batteries give more current than the AAA cell batteries. Because of the size difference in the batteries, AAA batteries hold a smaller amount of material than AA batteries

    Read more: http://www.ehow.com/about_6756596_difference-between-aa-aaa-batteries.html#ixzz2q3TEbRyy
     
  2. jcsd
  3. Jan 10, 2014 #2

    berkeman

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    I didn't bother reading the ehow explanation.

    There is more *energy* in a single D cell compared to a single AA cell. Yes, you can get more peak current out of the D cell too, because the equivalent series resistance (ESR) of the D cell is less, but that is irrelevant to your question of the light bulb.

    The D cell will be able to power the light bulb for much longer than the AA cell, because of the higher energy storage. The output voltages are the same initially, and the bulb resistance is the same, so by V=IR, the currents will be the same. The D cell will be able to supply that current for a longer time, because the output voltage will not droop for a much longer time (the output voltage droops when the battery gets near to running out of stored energy).

    Makes sense?
     
    Last edited: Jan 10, 2014
  4. Jan 11, 2014 #3

    tony873004

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    Battery capacity is measured in mAh. That's milli Amp hours. That's a unit of electric charge. That's how many hours they can reliably supply a certain amount of milliamps of current.

    D's have big mAh. AAA's have small mAh. 8 of either will power my boombox at full volume. The AAA's will just die sooner. I was just looking at a AAA battery. Even with my reading glasses I couldn't read the rating, but they typically stamp the battery with its mAh.

    Burglar and fire alarms typically have heavy 12-V back-up batteries of 4 or 7 Amp hours. Alarms generally draw about 100 mA unless the siren or bell is ringing. So their backup batteries could power them for several days in the event of a power failure.

    An interesting thing about batteries is that their voltage is usually a multiple of 1.5 V. I don't know why 1.5 is such a standard. If you open up a 9V battery, you find 6 small 1.5 volt batteries. I imagine if I ever opened up one of the alarm back up batteries, I'd find 8 smaller batteries wired in series.
     
  5. Jan 11, 2014 #4
    The voltage of a singe battery cell depends on the electromotive force (e.m.f.) of the electrochemical cell used in the battery. Both "dry" (zinc-carbon) and "alkaline" (zinc-manganese dioxide with potassium hydroxide electrolyte) commonly used in house hold batteries have an e.m.f. of around 1.5 V but rechargeable batteries (Nickel-Cadmium and Nickel-metal hydride) use cells with an e.m.f. of 1.2 V.

    Other common types are Lead-acid (2.1V) and Lithium-Ion (about 3.6V).
     
    Last edited: Jan 11, 2014
  6. Jan 11, 2014 #5
    The D cell will be able to provide more current because it has less internal resistance. Think about how much current would flow if you short-circuited the battery. It won't be infinite because the battery has a certain amount of internal resistance. I don't know what the actual numbers are so I'll make some up for illustrative purposes. Suppose the short circuit current or a AAA is 6 amps, it must have an internal resistance of about 1/4 ohm. A D cell may have an internal resistance of 1/12 ohm and so provide a short circuit current of 18 amps. When you connect these batteries to a 3 ohm light bulb the total resistance of each circuit is 3 1/4 or 3 1/12 so more current will flow from the D cell but the difference will not be enough to notice. If you tried to power 12 such light bulbs in parallel you the total resistance of each circuit would be 1/2 ohm for the AAA or 1/3 ohm for the D cell. In this case the difference is significant and you would notice the bulbs on the D cell circuit shining brighter.
     
  7. Jan 11, 2014 #6
    Thank you everyone for your responses.
    Based what was written on the first quote above, I would think that the higher energy storage in the D battery is largely the result of a longer battery life. And I'm guessing that longer battery life has to do with the larger amount of material (more zinc would mean more positive zinc ions could be pulled into the carbon which would result in current produced for a longer period of time). True?

    On the second quote, is there less resistance in a D battery for a similar reason- more surface area of the zinc means more reaction with the carbon and therefore the battery can meet a larger demand for electrons (or has an easier time producing the current which would translate into lower resistance)?
     
  8. Jan 11, 2014 #7

    rcgldr

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    The "internal resistance" is due to the limit in rate of change of the chemical reactions within a battery required to maintain some level of power. Below is a link from a yahoo answers page, stating that size matters, but the linked to reference for carbon zinc batteries shows the same flash (duration about 1 second) peak current for AAA to C size carbon zinc batteries, about 5 amps.

    yahoo link:
    http://answers.yahoo.com/question/index?qid=20100718092233AAUpFkk

    battery spec link, description on page 10, chart on page 11:
    http://data.energizer.com/PDFs/carbonzinc_appman.pdf

    At least in the case of some types of rechargable batteries, it's possible to make high discharge / low internal resistance batteries. There's a contest radio control powered glider for an event called F5B that uses a 2 1/2 or so hp dc brushless motor in 2 to 5 second bursts. In the days of nicad batteries, 27 A size cells could produce 80 amps or so of current. These days, high end aerobatic radio control helicopters also have high power demands for short periods of time, and high discharge lipo batteries are used for the helis and F5B like models, rated at 25C, which means max amps = 25 x amp hour rating, peak currents: 25C x 3000mah = 75 amps, 25C x 4000 mah = 100 amps, 25C x 5000 mah = 125 amps.
     
    Last edited: Jan 11, 2014
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