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Batteries connected in parallel - Amps won´t add up?

  1. Feb 25, 2017 #1
    Batteries are connected in parallel. Multimeter shows: 1,5V AND... "0.12A" regardless of battery number. Volts stay the same but should not Amps add up in parallel? "0.12A" with 4, 5 or 6 batteries...

    3308ns5.jpg

    Details: Amps measured correctly by closing the circuit with multimeter probes (bulb lights up)
    Posted this under "physics education" because my question is trivial. I am very new to electronics.
     
  2. jcsd
  3. Feb 25, 2017 #2

    cnh1995

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    Homework Helper

    How?
    Have you studied Ohm's law?

    Also, post such conceptual questions in general physics or classical physics (or EE) forums. For posting in HH forums, you should fill up the three-part template with an attempt at a solution.
     
  4. Feb 25, 2017 #3

    gneill

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    Staff: Mentor

    Mod note: Thread moved to Electrical Engineering Forum.
     
  5. Feb 25, 2017 #4

    NascentOxygen

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    It seems that you are powering a light globe from some 1.5V cells, and you are finding that the current to the bulb stays unchanged regardless of how many cells you connect in parallel?

    Were you expecting that with more cells connected there would be more amps through your light globe?

    Contrast what you are doing here with what happens in a different experiment where you connect the extra cells in series.
     
  6. Feb 25, 2017 #5
    Yes. One 1,5V battery cannot light the bulb up. When I connect batteries in parallel voltage remains the same "1,5V" (regardless of how many batteries I connect), so something else must change since the light NOW shines with 4, 5 or 6 batteries connected in parallel.
    When you connect batteries in series voltage rises, amps stay the same - so I thought when you connect batteries in parallel voltage stays the same, but amps rise. Otherwise why is the bulb shining with 5 batteries and not with 1, when voltage is 1,5V in both cases?
     
  7. Feb 25, 2017 #6

    NascentOxygen

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    Something else is going on, something that you haven't considered. When you measure the voltage and report it as being 1.5V, you should be measuring the voltage across the light globe when it's powered. So connect your meter across the light globe and tell us that voltage with 1 cell, then with 2 cells, and so on.

    Amps stay the same? Can you use Ohm's Law to show that you are right?

    Something else is happening to confuse you.
     
  8. Feb 25, 2017 #7

    Averagesupernova

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    Batteries in parallel increase the available amps. You have a light bulb in circuit which at a given voltage requires a specific number of amps. Once you have enough batteries in parallel to able to source the number of amps required, you can add as many batteries as you wish and it will make no difference other than it will take longer to run the batteries down.
     
  9. Feb 27, 2017 #8
    Batteries are rated in amp/hours, not amps (automotive batteries are also rated in CCA but that's a different ball of wax and still a measure of current over time).

    If you connect batteries in parallel, the voltage remains the same, thus the current remains the same across the same load. If you connect a 12 Vdc battery across a 24 ohm resistor, you will induce a current flow of 0.5 amps. It doesn't matter whether the battery has a storage capacity of 3 amp/hours or 300 amp/hours. If you want to increase the current through the load you need to increase the voltage of your power supply or decrease the resistance of the load.
     
  10. Feb 27, 2017 #9

    NascentOxygen

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    That should not be read as "Batteries are rated in amperes per hours, not amperes." because that would be incorrect.

    What it should be is "Batteries are rated in ampere hours, not amperes". Though in the exercise in question, even with the correction it seems unhelpful because it is difficult to construe that to account for OP's observation.
     
  11. Feb 27, 2017 #10
    The amount of current which flows is determined by the resistance of the bulb and the supply voltage.
    These will be more or less the same regardless of how many parallel batteries you have.
    (The bulb resistance might vary a small amount when hot at opposed to cold, but not enough to make much difference)
     
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