Neagive and Positive of 12v Battery

Discussion in 'General Electronics Chat' started by foolios, Aug 10, 2014.

  1. foolios

    Thread Starter Active Member

    Feb 4, 2009
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    If the leads from the terminals, either one, were connected singly(only one at a time) to a separate ground like a ground rod. There would be a flow of electrons right? Either post will have a higher voltage than ground, yes?
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    No. In a battery, there are two electrochemical half-cells. The two half-cells must be connected into a full circuit to allow electrons to flow. If the answer was "yes" then the battery cell would become increasingly positively charged over time as the electrons spilled (flowed) out. This is not allowed by physics - as a general rule.
     
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  3. to3metalcan

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    Jul 20, 2014
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    Voltage is always relative...if the ground isn't connected to one side or the other of the battery, it has no relationship with the charges in the battery. This is why ground is also called "common"...it has to have a connection in "common" with everything it's grounding.
     
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  4. foolios

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    Feb 4, 2009
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    From somewhere I read:
    In battery system one of the two poles is for example negative and the other is more negative in comparison.
    This made me think that if there was a connection to an object that had more or less electrons, that energy from a battery could flow. Like into the ground rod.
    If the positive side of a battery was grounded.
    Oi...
    So grounding a battery's terminal(+/-) isn't dangerous as long as there isn't a route to its other post? So even if another battery was connected along that ground with it's opposite post, there won't be any flow present then either, right?
    I guess that makes sense as I've connected batteries in series all over the place.
    Geez, I never really explored this before. Why doesn't energy want to flow between the batteries opposite terminals?
    I guess it's not as simple as one side has more electrons than the other and wants to flow to that. 'Cause that would mean direct shorts as soon as opposite posts of batteries are connected. Well, as long as only one set of them are anyhows.
     
  5. nsaspook

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    Aug 27, 2009
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    In a battery (like lead acid) the current flows via ions in the electrolyte (acid) not electrons because the electrolyte has no free electrons like a metal conductor has. Battery electro-chemistry is complex but basically when the compounds form from cell reactions they move across the electrolyte in both directions from the lead plates leaving an excess amount of electrons on one plate and a deficit of electrons on the other. The total amount of electrons remains the same but they are separated creating a electric field between them (cell voltage) that eventually reaches the point where it stops the chemical reactions and movement of (electrical) charge. At this point the battery is in equilibrium like a balance beam so no energy flows within the battery until it's unbalanced by connecting a circuit that allows electrons to flow externally between the plate terminals. This unbalance causes the chemical reactions to restart moving ions across the electrolyte to reestablish equilibrium and maintains cell voltage as current flows in the circuit.

    What's important to remember is that the total number of electrons in the battery and circuit doesn't change , they only move slowly in a loop pushed by the voltage potential of the battery. So when you 'charge' or 'discharge' the battery you don't add or subtract electrons, you add or subtract energy that is stored or drawn from the battery via chemical reactions that move electrical charge but don't change it's total number.

    A capacator is much the same but instead of chemical reactions the energy is stored in a electric field.
     
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  6. to3metalcan

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    Jul 20, 2014
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    Nope, but if you connect the second battery back to the first one's opposite post (I mean, don't, they'll explode without some kind of load between them) then they'd have a common connection. This is actually what "circuit" means...just like any other kind of circuit, in an electrical circuit there has to be a way to get back to where you started.
     
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  7. alfacliff

    Well-Known Member

    Dec 13, 2013
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    look up complete circuit. the terminals are only ppositive and negative referenced to eachother. it takes a complete circuit from positive to tnegative to omplete the circuit and allow current to flow. it cant be just any old positive and negative, they muxt be a complete circuit.
     
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  8. wayneh

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    Sep 9, 2010
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    This reminds me of a discussion not long ago in these forums, about a bird sitting on a high voltage power line. Compared to ground, the bird assumes a voltage of 100kV. But as long as the air is not conductive, there is no path to ground and current cannot flow. The bird has no idea.
     
  9. foolios

    Thread Starter Active Member

    Feb 4, 2009
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    the electrolyte in both directions from the lead plates leaving an excess amount of electrons on one plate and a deficit of electrons on the other.

    I think my learning of ac has really caused me to struggle with trying to understand dc.
    But if I try to relate the two, ac acts kinda like a battery in that if a hot leg is grounded, that energy wants to find it's way back to it's origin; like through a grounding rod, into the ground and prolly back up a different grounding point that leads back up the telephone pole and back into the circuit.

    So I'm looking at the positive and negative of a battery and I'm thinking the same thing, that the energy wants to go from one side of the battery to the other. What amazes me is that the energy won't try to equalize with the opposite post of another battery. Especially after rereading and thinking about the whole one side has more and the other less.
    I can see how with a battery being portable that it's not possible to find a path(circuit) back to itself just by grounding it via a grounding rod or separate ground. I think the ion idea helps explain why it doesn't just bleed out energy the moment a battery grounds out. Thanks for that.
    But I am still confused as to why the charge isn't affected when opposite poles of two batteries are connected. We have what you have described as an abundance and deficiency. Why no reaction/energy release?

    Thanks for your time, I'm gonna keep mulling this over.
     
  10. MaxHeadRoom

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    Jul 18, 2013
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    This is only if you intend to use Earth ground as a conductor.
    See ch 2 here.
    http://www.ese.upenn.edu/detkin/instruments/misctutorials/Ground/grd.html
    Max.
     
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  11. crutschow

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    Mar 14, 2008
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    I think all you questions can be answered by following this one rule of electricity. You always have to have a complete circuit for any current to flow. Connecting one terminal of anything to anything else thus has no significant effect if there's no return path for the current.
     
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  12. nsaspook

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    Aug 27, 2009
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    It's important to remember that charge is not energy. When you connect the opposite poles of two isolated batteries where is the path for energy flow? The charge distribution will change when there is a path for energy to flow from one point in space to another. Most of the time that requires a circuit.

    The overall amount of charge isn't effected by connecting two isolated batteries but the potential electric fields (from that abundance and deficiency) distribution in space from each of the batteries is if they are moved in relative position (accelerated) to each other (usually much quicker than you could do manually) generating a EM field (that transports energy in space/vacuum without a physical circuit). It's obviously easier to move light electrons in a conductor to generate the needed field energy than to shake a heavy battery to generate a time varying electric field needed to transport energy in space.
     
    Last edited: Aug 13, 2014
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  13. alfacliff

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    there are some circumstances where one wire is enough, like corona loss at extremely high voltages, where is the circuit that corona loss takes? and lightning, where is the complete circuit for cloud to cloud lightning? but at normal voltages, you have to have a complete circuit.
     
  14. nsaspook

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    Aug 27, 2009
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    The complete circuit is always the universe at large but it's effect is usually very small with typical electronic circuits where the components focus the fields tightly between and around conductors so we can ignore it except when we need to radiate energy with something like an antenna.
     
  15. foolios

    Thread Starter Active Member

    Feb 4, 2009
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    I am confused by these two sentences.
    They seem to be stating opposing things about electron movement.
     
  16. nsaspook

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    It's confusing if you believe that electrons are somehow stored in a battery (or capacitor) when it is 'charged'. A battery is energized (a better word for what's happening) by electron redistribution (current by the movement of ions in the electrolyte) that produces an electric field between the plates.

    This process is call Electro-chemistry:
    http://crescentok.com/staff/jaskew/isr/tigerchem/ionic/electrochem.htm

    The main thing you should look at is how it explains the different types of conduction and potentials. Batteries are not 'electronic' so we can't use the regular circuit theory simplification of energy flow via electrons to understand the operation of a battery. You must go deeper to understand charge and how potential energy moves charge.
     
    Last edited: Aug 27, 2014
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  17. foolios

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    Feb 4, 2009
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    Thank you so much for continuing with your elaboration.
    It has helped me very much.
     
  18. MikeML

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    Oct 2, 2009
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    This image shows how electrons (and other charge carriers) flow

    hint: they don't, actually
     
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  19. foolios

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    Feb 4, 2009
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    That's neat. Thanks for that.
     
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