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Basic Electronics » Very Basic Batteries in a Series Question

November 17, 2011
by vladarino
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I am new to electronics and working through understanding various concepts. I read that when you connect two of the same type of batteries in series the voltage between two points in a circuit is double that of either battery.

What I don't understand is when you actually touch the positive end of one battery to the negative end of the other (required to put them in series), why don't those two terminals immediately "equalize" their electron differences? Doesn't one have a higher number of free electrons than the other? Why don't electrons from one terminal immediately flow to the other battery's terminal even if the batteries are not connected in a circuit.

Thanks for the clarification.

November 17, 2011
by Ralphxyz
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I do not undersand your question (at all).

You can google "batteries in series" to see some good explanations.

Here is a nice illustration from tumblr.com:

Ralph

November 18, 2011
by vladarino
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Thanks for the link ralphxyz. Yes, I've done google searches. The site you ointed me too is a good one too.

What I meant to say is if you make the positive end of one battery touch the negative end of another, you have have a situation where an anode is touching a cathode (like a wire connecting the two). Then why doesn't some current develop between those two terminals?

If that still doesn't make sense we can just leave it at that.

November 18, 2011
by Ralphxyz
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Not know what the h^ll I am talking about I'd say because there is no ground.

Or that there is no circular circuit You have - to + but you need something to return to - again.

Amazing my answer actually makes sense to me, we need mongo or bobamosfet or some of the other knowledgeable folks to actually explain this.

This actually is a good electronics theory question and deserves an answer other than mine.

Ralph

November 18, 2011
by rajabalu21
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When the cathode and anode are touching each other directly then there is no potential difference between them. They are at the same voltage and so no current flows.

Apart from a closed circuit, you need 3 things; Cathode, Anode and Electrolyte for the current to flow.

-Raja

November 18, 2011
by mongo
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Vlad,

If you have two D cells in a series circuit, the point where they make the connection has potential to only the ends of either battery. If you measure the voltage from there to either end of the stack, you will have either +1.5V or -1.5V. From end to end of the stack, you have 3V and depending on which meter lead you have on the + side, you could have either +3V or -3V.

The junction between the batteries is just half way to either end.

Most power supplies use the negative end of the supply as the common or ground voltage. So from there, you have two different voltages. At the middle, there is a +1.5V potential and at the top of the stack is +3V potential. Nothing is cancelled out, they just add up as more cells are placed in the stack. From the negative end, you have a series of voltages from 1.5, 3, 4.5, 6 7.5 volts, and so on.

November 18, 2011
by mongo
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Oh... By the way - there are no free electrons. Since there is no electron flow, they are static. (not as a static charge, but as not moving)

November 18, 2011
by vladarino
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rajabalu21 gets at my real question. I realize now that it's not the "batteries in a series" aspect I don't understand. It's the whole idea of what is required for a current to flow. Having a + and - touch is not enough.

Why does a current not flow if you touch the + of a C battery to the - of another C battery? According to rajabalu21's explanation there is no current because there is no electrolyte between the two terminals them and an actual circuit is also missing. This brings to mind the lemon powered light bulb experiments. One electrode in the lemon is the anode, the other is cathode, the lemon is the electrolyte and you don't get a current until you connect the two electodes with a wire.

Thanks for the insight guys.

December 18, 2011
by sdebaun
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Vlad, I believe the key "ingredient" is a closed circuit. If you have that then yes, the current WILL flow from one battery terminal to the next... but if there is no closed circuit then your batteries will remain static and do nothing. ( Retain their charge... I mean potential.)

In your example, there is nowhere for the current to go. It can't simply move to the next battery because they are touching. If that was the case batteries wouldn't be very useful..

Build a test station with batteries and light bulbs using series and parallel circuits... test with a multimeter until the light bulb goes off above your head!

December 23, 2011
by huzbum
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The battery is actually powered by a chemical reaction. There is an anode and cathode submerged in an electrolyte. Each is composed of different materials that react with the electrolyte in a certain way when there is a complete path for electrons to flow.

The electrolyte reacts with the anode and electrons are transferred from the electrolyte to the anode, meanwhile the cathode reacts with the electrolyte and transfers electrons (which it gets from the anode through the circuit) to the electrolyte and the circuit is actually completed through the electrolyte.

These reactions use up chemicals in the battery, and that's when the battery goes dead. Some batteries can reverse this process when a stronger electrical potential is applied to the battery terminals, but eventually the electrodes (anode and cathode) are damaged and with each cycle some of the electrolyte is converted into less useful byproducts diminishing its' capacity.

When you touch the negative of one battery to the positive of the other battery, the circuit is not complete because there is no path to return electrons to the electrolyte in the first battery to complete the reaction, and no chemical reaction in the second battery to remove electrons from the electrolyte to make the cathode positive.

February 08, 2012
by benlbroussard
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Batteries and voltage had me stumped for quite some time. I just read the wikipedia page on alkaline batteries, http://en.wikipedia.org/wiki/Alkaline_battery, and the Chemistry section was my eureka moment.

The Chemistry behind the battery reactions and the battery construction are key here. The anode connects to the negative terminal and the cathode connects to the positive terminal.

Battery Parts

Eq -: Zn(s) + 2OH−(aq) → ZnO(s) + H2O(l) + 2e−

Eq +: 2MnO2(s) + H2O(l) + 2e− →Mn2O3(s) + 2OH−(aq)

I apologize for the lack of super and subscripts, but on to the explanation. When a battery is not part of a circuit, it reaches an equilibrium state. Eq - occurs which decreases the number of OH- molecules, and saturates the negative terminal with free electrons. The decrease in OH- molecules makes Eq + more likely to happen in the presence of free electrons. These free electrons on the anode, and willingness to take on free electrons at the cathode is measured as a voltage. Note that the electrolyte solution allows OH- and H2O molecules to flow back and forth, but it is an insulator against the flow of free electrons.

Now for the good stuff: connecting batteries in series. As an example, I will walk through what happens when you connect the cathode of battery one (B1) to the anode of battery two (B2).

1) Free electrons from the anode of B2 travel to the cathode of B1 causing Eq + to occur. 2) Eq + in B1 causes an increase in OH- molecules in the electrolyte solution, while Eq - in B2 causes a decrease in OH- molecules in its electrolyte solution. 3) OH- increase in B1 causes Eq - to occur adding more free electrons to its anode. The OH- decrease in B2 makes Eq + more likely to occur in the presence of free electrons. 4) B1 reaches equilibrium again as Eq - slows and then stops due to the mutual repulsion of the free electrons and the OH- molecules. This saturation of negative charge at the anode means a saturation of OH- molecules which stops Eq + at the cathode of B1. A lack of Eq + by B1 means a lack of electron transfer from the anode of B2 to the cathode of B1. Finally the OH- levels in B2 have dropped due to Eq - having occurred more, and thus the affinity for free electrons at the cathode of B2 has similarly increased.

This is how I think it works. Experts out there, please adjust what is incorrect.

February 09, 2012
by mongo
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That pretty much sums it up... Batteries in series have the potentials added together. True, the potential is there but without a closed circuit, that is all you have - potential. Once you close the circuit, you turn the potential into work.

Chemical processes happen in a battery even without a load through internal conductivity, which is why batteries go dead, even if not used. It just takes a long time. As you put a load on a battery, the chemical processes increase to maintain a balance of sorts. If you go beyond the battery's capacity to maintain that balance, your output voltage will drop. The bigger batteries have higher capacity for maintaining the balance than the little ones. Makes sense huh?

If each battery has the potential of 1.5 volts, each time that you add one in series, you increase that potential from one end of the stack to the other by that same 1.5 volts. You can tap into the different potentials along the way for different voltages. If all of them are the same, you still have the capacity in amps with one as you would with ten but the voltage is different.

Now, if you put these same batteries in parallel, your voltage will not change but the current in amps will increase with each additional battery. Two is twice the current as one and so on.

But... Unless there is a closed circuit, where the electrons can move through from the negative to the positive side of the battery or the stack, there is no work done.

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