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basic battery question

Discussion in 'Electronic Basics' started by Christian Blondin, Feb 13, 2004.

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  1. Being fairly new to electronics, and not an engineering student, I found
    out something that I can't explain: why can't current go from one battery
    to the other, such as this:

    | |
    | + |
    --- -
    - 1.5V ---
    --- 1.5V -
    - ---
    | + |
    | |

    I know that if I connect the two other poles together I get an instant
    short circuit.

    I thought on the + side of the battery there were always 'holes', and in
    the - side excess electrons. Normally they should flow from one to the
    other. Is it something chemical?
  2. CFoley1064

    CFoley1064 Guest

    Subject: basic battery question
    Current flows from one place to another based on differences in potential --
    i.e. voltage. Since they're both 1.5V batteries, you won't see much difference
    in potential between the two. However, real-world batteries do have minor
    differences in voltage, dependent on such things as age and use. So you will
    get some current flow between batteries if you do this.

    Generally, hooking up batteries in parallel like this is *not* a good idea --
    they're not made to do that. If you hook up two batteries in parallel like
    this, you'll almost never get twice the "life" (amp-hours -- amps of load
    current * number of hours, the measure of battery capability) out of them as
    you would from a single battery. Sometimes you can even damage one battery,
    leading to less "life" (total amp-hour output) than you would from a single
    battery on its own, because the second damaged battery acts like a draining
    load on the first, using up energy. If this is happening, you may find that
    one of the batteries is getting warm or hot -- it's being heated by the other.

    Good luck
  3. Olaf

    Olaf Guest

    of course a battery is a chemical device, but that's not the point here.
    You seem to think of a battery as having to sides, one with to much
    electrons and one side with to little. Though this can explain some
    circuit behaviour you'ld better think of a battery as a charge pump. The
    charge is made up of electrons and the battery creates a force. But a
    battery cannot compress electrons inside a wire or inside a battery.
    Neither can it suck them out of a piece of wire. A battery just tries to
    move the file of electrons inside the wire and the other components.

    Now it should be clear why nothings happens (I hope ;-): the left battery
    tries to push electrons inside the lower piece of wire (not possible), the
    right battery tries to suck electrons out of the lowers right piece of
    wire (not possible) and they both try to move the electrons in the upper
    piece from right to left. But these electrons have no place to go, and
    there aren't any electrons available on the right side to fill them up. So
    nothing happens.

    And in correction to Chris's post, the batteries in your circuit are
    connected in series and there is no problem in this. Most battery operated
    devices use batteries this way. Your circuit may be considered as a single
    3.0V battery.

    hope this clarifies?

    bye, Olaf
  4. grahamk

    grahamk Guest

    Redraw the circuit by sliding the RH battery so that it sits on top of the LH battery.
    You now have a 3 volt battery with positive and negative terminals.
    No current can flow until you connect a device such as a 3 volt lamp between these terminals.
  5. Thank you all for your replies, and long live newsgroups.
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