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What is the output current of two batteries in series?

  1. Oct 15, 2015 #1
    when they have the same properties , the same current circulates in them because they are in series .. but the question is how to define the output current when there are two batteries , one in good health and the other defective so one deliver a high current and the other a lower one ?
    thank you for your help !!
     
  2. jcsd
  3. Oct 15, 2015 #2

    BvU

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    Hello Ikari, welcome to PF :smile: !

    still holds !
     
  4. Oct 15, 2015 #3
    thank you :D

    well actually given the chemical and physical properties of the batteries , the same current circulates in them when they operate at the same conditions , but when for example a battery delivers let's say I=2A and the other I=0.5 , which current would be the output ?

    thank you again !!
     
  5. Oct 15, 2015 #4

    BvU

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    It would be 0.5 A according to
    .

    There is a question mark to be placed here: If you put two batteries in series, the combination delivers a higher voltage, so the 'bad' battery doesn't have to "push" that hard, which means it may be able to deliver a bit more current.

    Batteries are sold as "voltage providers" (you buy a 1.5 V battery, not a 0.5 A battery).
    Ideal voltage providers deliver the nominal voltage, no matter what current is flowing. They don't exist (fortunately -- or there would be a lot more fires).

    Our first approximation to describe the behavior of real batteries is to assume there is an internal resistance inside the battery. So if our 1.5 volt battery has to deliver 1 A and the actual voltage provided is 1.25 V we say that the internal resistance takes away 0.25 V at 1 A. Ohm's law tells us the internal resistance must be 0.25 Ω.

    Actual batteries don't have such a simple linear behaviour for V as a function of I.
     
  6. Oct 15, 2015 #5
    Absolutely. A battery provides a certain voltage, say in this case, 1.5 V. If you have two such batteries in series, together they provide 3 V. provided both of them are still alive. It is not they they "give" a certain current. The current depends on the circuit that you connect. If, with the two batteries in series, you connect a 10 ohm resistor, you draw a current of 0.3 A. If you connect a 1 ohm resistor, you draw 3 A. This is assuming that the batteries are ideal, with zero internal resistance. For real batteries, you just add the internal resistance to the outside resistance you connected, in series. If you draw more current by using two small a resistance in the circuit, you just kill the battery sooner.
     
  7. Oct 15, 2015 #6

    CWatters

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    The question is invalid.

    Two batteries in series will ALWAYS deliver the same current. It's not possible for them to deliver different currents if they are in series.

    Two batteries in parallel could deliver different currents.
     
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