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Can you explain voltage sources in series and parallel completely?

  1. Jun 22, 2014 #1
    i would like to know the underlying reasoning why it works the way it does and how it works based on the explanation given by the book Electricity Demystified, but i would like a far better explanation. Give me something like an analogy to better explain it physically.
    In there it says:
    for voltage sources in series:
    E = E1 + E2 + E3 + ...+En (all connected "minus to plus"
    with polarity reversal: it is
    E = E1-E2+E3+...+En (reverse the polarity of battery number 2 with voltage E2)

    for voltage sources in parallel:
    in a parallel circuit, the poles must all go "plus-to-plus" and "minus to minus"
    the output voltage of a properly designed parallel combination of cells or batteries equals the voltage of any single one of them.

    (i think this is due to kirchoff's voltage law). i would like a of this schematic/drawing of this circumstance.

    I have to understand this logically to progress through.
  2. jcsd
  3. Jun 22, 2014 #2
  4. Jun 22, 2014 #3
  5. Jun 22, 2014 #4
    i don't think amasci.com has what i need
  6. Jun 22, 2014 #5
  7. Jun 22, 2014 #6

    jim hardy

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    To better understand the nature of your request;

    What is your understanding of these terms?

    joule, coulomb, volt, ampere, ohm , watt, ?

    Meantime you might experiment with a two or three cell flashlight.
  8. Jun 22, 2014 #7
  9. Jun 22, 2014 #8


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    Keep in mind that ideal voltage sources in parallel are impossible, it only works with ones in the real world and even then it's a bad idea if the sources are very far off from each other in voltage. Best case is that the lowest voltage one blocks reverse current in which case it is effectively out of the circuit so would be pointless and worst case is it will NOT block reverse current and be damaged.
  10. Jun 22, 2014 #9
    I don't think i can experiment to any helpful use with a two or three cell flashlight.
    Joule-unit of energy in SI derived units
    coulomb-a unit of charge (electrons)
    volt-the electrical potential energy that a battery has that allows it to release current and energy
    ampere-Coulombs / second that pass through a point in a circuit
    ohm- voltage/current ratio. tells how resistance a resistor has in a circuit
    watt-J/s or joules per second

    this doesn't help me learn the exact details of what i am asking because i already knew it
  11. Jun 22, 2014 #10
    that sounds a bit esoteric to me.

    Let me reword and formulate my own explanation.
    it is impossible to have ideal voltage sources in parallel because you can not have each voltage source (battery), giving out the same voltage precisely as voltage of battery are not always precisely equal due to being partly random and not exactly same.

    my explanation is that if you have a voltage source in parallel, as in a battery connected in one of the branches of the parallel circuit, if it was the same voltage as the original start battery, it won't change the voltage due to the voltages of the two batteries being the same, nothing changes in the "electrical pressure".

    the reasoning for adding a battery in this branch is to increase more current than a single battery can do on its own. "if the voltages differ, some of the cells or batteries will drive current through others and that's no good! (seems ambiguous wording, what is drive current through others?)"

    quote "Best case is that the lowest voltage one blocks reverse current in which case it is effectively out of the circuit so would be pointless and worst case is it will NOT block reverse current and be damaged."
    i don't know what this means. please try rewording it.
  12. Jun 22, 2014 #11
    more related helpful links:
    A Question about Voltage Sources in Parallel https://www.physicsforums.com/showthread.php?t=716941
    Two different voltage sources in parallel ! https://www.physicsforums.com/showthread.php?t=634530
    Parallel voltage sources circuit https://www.physicsforums.com/showthread.php?t=512536
    Two Parallel Voltage sources and KVL https://www.physicsforums.com/showthread.php?t=435172
    connect two AC sources in parallel unless they have the same voltage https://www.physicsforums.com/showthread.php?t=321292
  13. Jun 22, 2014 #12


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    Let's say you have a 12volt battery and a 1.5volt battery and you hook them in parallel. The 12v will want to push current through the 1.5 volt battery the wrong way. If the 1.5volt battery blocks current that tries to flow through it in the wrong direction then the effective circuit is a 12volt battery and the 1.5 volt battery is not really there.

    If the 1.5 volt battery does NOT block reverse current, then it will be swamped with reverse current from the 12volt battery and it may well explode or at the very least be irreparably damaged.

    Voltage Power supplies, on the other hand, always (as far as I know) are circuits that have diodes and or transistors in the output path and so naturally block the flow of reverse current so won't be damaged if put in parallel, but the lower voltage one effectively won't be there since its output will be reverse biased.
  14. Jun 22, 2014 #13
    it's hard to understand

    let me draw a picture of the circuit or could you possibly do that for me? with comments on it labeling every process/action? i'm not good at learning through words only as it is very confusing for me. i could use an animation to learn best as well but i don't know how to use flash animation to do that.
    Last edited: Jun 22, 2014
  15. Jun 22, 2014 #14
    phinds, here is a simple diagram i made. hopefully you can edit it to your explanation

    Attached Files:

  16. Jun 22, 2014 #15
  17. Jun 22, 2014 #16

    jim hardy

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    well you could put one cell in backwards and observe the light glowing more dimly. That would confirm what your book says about voltages in series.



    RAZZZ A volt is one joule per coulomb. It is a measure of the energy required to move a coulomb from one place to another. "One place to another" is significant in that it infers a difference not an absolute value - in circuits, voltage is always a potential(energy) difference.

    well done !

    I shoulda added to the list , "node" .

    it is not clear to me exactly what you are asking.

    It is helpful when starting out to imagine one's self infinitesimally small and inside the circuit drifting along with the [STRIKE]electrons[/STRIKE] charge carriers. [in modern texts, 'conventional' current flow is in opposite direction to electron drift - start out your thinking with conventional current and you'll save yourself a lot of headaches]

    In a DC series circuit, as you progress through each circuit element you either acquire or lose energy.
    That is why the voltage(potential difference) between the ends of your journey is the sum of the individual voltages(potential differences) including their signs.

    In a DC parallel circuit you have only one beginning point and one end point, but with multiple routes to get from one to the other. Between those two points exists only one potential difference.
    That is why batteries in parallel must be connected with like polarity, else you have a war of the batteries each trying to impose its potential across the other.

    Have fun

    old jim
  18. Jun 22, 2014 #17
    node-simple a point of connection of two or more circuit elements. but pictorially i don't know what this means. i would guess that it is the dot on a schematic drawing between two elements such as source battery and resistor in each parallel branch.
  19. Jun 22, 2014 #18
    jim hardy i am trying to learn the step by step explanation of how voltage sources in series/parallel circuit works. and electrical theory underlying it. in other words what precisely and exactly makes it work the way it do? explain in micro detail like an animation pictorially how it works with step by step explaining in full.

    for ex, i will toss out an explanation that may or may not be correct: my explanation would be it changes the path of the current. and it goes this particular way (shown in a diagram/animation)
  20. Jun 22, 2014 #19
    here is a diagram i drew myself of voltage sources in series.

    Attached Files:

  21. Jun 22, 2014 #20
    The basic answer is that voltage sources are applied electric fields, and they add in series. When put in parallel, the required current is proportionally divided between them. If this is not a good enough answer, then you have some trouble. Going further into the rabbit hole requires going into some depth with Maxwell's equations. Its a simple enough question, but one that can potentially have a pretty complex answer, depending on how deep into electrical theory you want to go. There are layers of abstraction here that can require some serious knowledge to peel away. Most people can accept that voltage sources add in series without needing to understand the field theory or quantum dynamics.
  22. Jun 22, 2014 #21
    refer to diagram in previous post
    so why is a negative terminal of the "main source battery/MSB" connecting to a negative terminal of another 6V battery? just explain this.

    i would have thought normally negative current from negative terminal would go to a positive terminal of the same battery. what happens to the current after "MSB's negative terminal electrons reach the 6V battery's negative terminal? where does it go next? and where does it travel precisely?
  23. Jun 22, 2014 #22
    what is an applied electric field? provide me an easy to understand answer.
  24. Jun 22, 2014 #23
  25. Jun 22, 2014 #24
    you have no current because you have an open circuit.
    The voltage difference between the + sign on the bottom and the - sign on the bottom is 30 V.
    The voltage difference between the - sign on the bottom and the - sign of the 6V battery is 0. Does this help?
  26. Jun 22, 2014 #25
    um actually it's not an open circuit, you just may have interpreted it wrong. there is no hole in the circuit. i was supposed to put E in the gap at the source battery. i will have to trace through what you are saying as it seems a bit unclear.
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