Several Voltage Source in Parallel

  1. About:
    I'm currently working on programming a basic circuit simulator for a game. One of the things i don't have a sure answer on is parallel voltage sources. I understand from what I've read so far that when two sources are in parallel the lower of the two gets overloaded. If they are the same voltage the current adds up which is easy for me to understand. It is also easy for me to implement in code but i need to make sure this holds up in larger designs.

    Questions:
    If a branch has several sources in it that may not be the same voltage what will happen? Will the lower voltage sources get reverse flow of electrons? Will the voltage drop any as a result of the reverse flow? If only a few sources have lower voltage than the others how does this effect the higher voltage sources? If only a few sources have higher voltage than the rest will if effect all or a few of the sources connected to it?

    Note: I'm mainly looking for wiring circuit understanding as most of the parts are already created. So i need to understand how several sources will effect my branch total voltage and amp output.
     
    Last edited: Dec 22, 2013
  2. jcsd
  3. It's all depend on internal resistance of this sources. If this resistance is low (the voltage source can supply high amount of current). You will end up with overloaded.
     
  4. hmm nearly forgot about internal resistance. Say in my case though that my sources had diodes to prevent reverse flow of energy. Would they simple be ignored as they can't over come the pressure applied on their inputs. As well would the voltage drop any to prevent that source from outputting?
     
  5. In this case (with a diodes) you don't have to worry about overload. The diode will prevent this.
     
  6. Not worried to much with overload as that is a simple matter to program. What i'm looking to figure outs is the circuit half of the understanding. As in what will be my total voltage, and amp output of the sum of all sources in the branch. I might edit the OP to make that clearer.
     
  7. vk6kro

    vk6kro 4,059
    Science Advisor

    Suppose you have a 12 volt battery and a 6 volt battery in parallel with the same polarity.

    Assume each battery has 1 ohm internal resistance.

    Going around the circuit there is a total of 2 ohms resistance and the 6 volt battery voltage subtracts from the 12 volts of the other battery because their polarities are opposite as you go around.
    Do you need a diagram for this?

    So there is 6 volts nett voltage driving current through 2 ohms.
    So, using Ohm's Law, the current circulating through both batteries will be 3 amps.
     
    1 person likes this.
  8. phinds

    phinds 9,148
    Gold Member

    Putting voltage sources in parallel is a terrible idea. If they are ideal sources, it creates a literally impossible situation and if they are real sources, it creates either (1) a dangerous situation if you don't use diodes, or (2) a useless situation if you do use diodes. There is no such thing as real sources that have the same exact voltage.

    What vk6kro says is true ONLY if the batteries don't explode when current goes through them the wrong way, and I would not count on that.
     
  9. sophiecentaur

    sophiecentaur 13,899
    Science Advisor
    Gold Member

    Sounds to me like your idea must be how to construct a smoke making machine. Whatever answer you get from any simulation will depend entirely upon what assumptions the simulation software makes. It really should chuck the whole idea out as a non starter rather than help you to get 'a result'.
    If you want some real fun, go out into a field somewhere, with a 12V and 6V car batteries. Then connect them together in parallel with some 5mm wire and fat crock clips. Be careful 'cos you may blow the side off one of the batteries. Car batteries are the nearest thing to voltage sources that you can get hold of conveniently which have absolutely no in-built protection.
     
  10. vk6kro

    vk6kro 4,059
    Science Advisor

    It was a hypothetical question, but I chose 12 volt and 6 volt batteries as these are likely to be lead acid types and therefore rechargeable.

    Charging a lead acid battery (as you would know) involves reversing the current flow.

    Starting a car by using another car's battery involves putting two batteries in parallel.

    Used cautiously, this process seldom causes explosions.
     
  11. phinds

    phinds 9,148
    Gold Member

    Fair enough. I'm still not so sure, though, about a 12v battery recharging a 6v battery but maybe it wouldn't cause meltdown or an explosion. Maybe :smile:
     
  12. vk6kro

    vk6kro 4,059
    Science Advisor

    Mainly, I wanted to show that you could calculate the currents involved if you had enough information.

    The next step is to show that putting a diode in series with the 6 volt battery eliminates this battery from the circuit as the diode is then reverse biased.
     
  13. phinds

    phinds 9,148
    Gold Member

    Right. Which as I pointed out makes the whole exercise utterly pointless.
     
  14. Not sure if that was directed at me or vk6kro but i'm looking to create the code that makes the simulation software work. In which i'm asking these simple questions to confirm a few things. This way i don't create a false simulation by having it use the wrong assumptions. Also yes blowing up batteries in a field is fun if you have extra car batteries. You can get about the same result out of two AA.

    Ya your earlier post was actually helpful and look forward to you detailing what happens when diodes are involved.
     
  15. phinds

    phinds 9,148
    Gold Member

    You don't seem to be paying attention. He just SAID what happens when diodes are involved. Reread posts 11 and 12
     
  16. Thanks i read that as i had just got up so it didn't click right away. So it only just removes the source from the circuit with no other effects? If that is the case then i'm slowly getting to were i can get this simulator of mine working correctly.
     
  17. phinds

    phinds 9,148
    Gold Member

    Right. It make the whole idea of adding the lower voltage source and a diode utterly pointless, as I am now stating for the 3rd time.
     
  18. In some ways it does but at the same time i'm not designing the circuit. What i'm looking to do is understand what the circuit will do if i put it under X condition. So knowing that adding a diode just ignores the lower source is actual a bit thing. At the same time knowing that one battery can send energy threw another also helps me out.
     
  19. phinds

    phinds 9,148
    Gold Member

    fair enough

    Well, you need to tread carefully here. That is NOT always true for voltage sources. Lab work on electronic circuits does not normally use batteries, it uses power supplies and they are not subject to recharging like batteries and they may or may not (but most likely not) allow any reverse current flow.
     
  20. vk6kro

    vk6kro 4,059
    Science Advisor

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  21. That is why i asked the diode question as the few power supplies I've built use diodes for protection. Though i'm interested in what would happen if i had a power supply that allowed reverse current flow. I assume that nothing good would happen and at some point it would stop working.
     
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