Author Topic: Coin Battery  (Read 16999 times)

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richhagen

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Coin Battery
« on: March 30, 2012, 01:36:00 AM »
A Simple Coin Battery

This is probably a bit basic for this crowd, but I thought I would post this here in case someone wanted to use it for something.  Although I don't think the experiment is particularly dangerous, perform it at your own risk.

A couple of weeks back I was discussing power and energy with my son, who is 13 years old.  We were discussing how batteries work and I thought I would make a simple battery from raw materials available in the home to illustrate the idea.  It worked out rather well, so I thought I would redo the experiment and document it for anyone wishing to do something similar. 

 

We use batteries for all kinds of things, but where do they come from?  How do they work?  They start our cars, power our portable phones and electronic gadgets, remote controls, and computers but what do you really know about them? 

 

First a brief history of batteries.  It turns out that electrochemical batteries might be older than our recorded history.  In the 1930's archeologists uncovered terracotta jars near Baghdad, Iraq, from about 2000 years ago which some scientists believe might have been a form of primitive early battery, although there is debate about the exact purpose and function of the artifacts.  If these were used as batteries, the facts and uses of it were lost to history. 

Much later, in Europe in the mid 1700's, scientists discovered they could store charge in a primitive capacitor made of a glass jar lined with metal foil on both the inside and outside surfaces.  A charge could be built up and stored sufficient to give quite a shock by applying voltage across the foil layers which were separated or insulated from each other by the glass of the jar.  These primitive devises were named Leyden Jars, after the University of Leiden in the Netherlands, one of the places it was discovered.  Several jars could be connected together to store more energy.

The American inventor, Benjamin Franklin, coined the term Battery apparently after seeing and using Leyden jars connected together and being reminded of several cannons being grouped together which were known as a battery of cannon. 

In 1800 an Italian scientist by the name of Alessandro Volta made the first battery of relatively modern times.  His first battery consisted of stacks of dissimilar metals separated by an electrolyte piled one on top of the other.  It was known as a Voltaic Pile.  The term Volt a term for the unit of electromotive force, or potential difference is named after Volta in honor of his scientific achievements.  This experiment is going to be similar to some of his early work from around 1800.  Other inventors tried variations where the plates made of various metals were suspended in various electrolytes. 




This is an example of an early battery using zinc and copper plates.  In this battery the metal plates would be suspended in a solution of Potassium hydroxide.  Cells of this type were used in the railroad industry for many years in the early 1900's.  This item was for sale on the E-bay website, although no longer listed, and the photo is used with the permission of that seller.  Incidentally the battery pictured was made by the famous inventor Thomas Edison's battery company.

 

Various variations of these voltaic piles were made, and different designs using liquid filled containers to hold the electrolyte were tried.  All of these batteries were not able to be recharged, only to have their metal plates replaced once they deteriorated.  In 1859, a fellow by the name of Gaston Plante invented a battery which could be recharged by reversing the electrical current across the battery.  He used lead and lead oxide in his battery, in an electrolyte of sulfuric acid, and to this day, batteries using the same chemical components, and known as lead acid batteries are made and used as starting batteries in automobiles, among other things.

 

Nickel Cadmium and Nickel Iron batteries soon followed which could also be recharged.  In the late 1800's carbon zinc dry cells similar to those you can by today, often labeled as 'heavy duty' were developed.  Small sealed alkaline batteries followed in the 1950's, and a plethora of different battery chemistries and configurations have followed to this day. 

 

All of these batteries work on the basis of chemical reactions, hence the term for them of electrochemical batteries.  Some types can be recharged by reversing an electrical current across them, and others can not.  Those that can not be recharged are referred to as 'primary' batteries, and those that can be recharged are referred to as 'secondary' batteries.

 

The chemistry of our experiment. 

 

For our experiment we are going to make a battery using U.S. Copper plated pennies and Zinc coated steel washers.  These items could really be any copper or copper plated coin, and any zinc or zinc coated coin, or disc.

 

Batteries utilize a class of reactions referred to as oxidation reduction reactions.  When one of the plates or reactants loses electrons it is said to be oxidized, and when one of the plates or reactants gains electrons it is said to be reduced.

 

When you put copper or zinc metal into an electrolyte, a solution which can conduct electricity, there is a tendency for the metal to dissolve a bit, which means that they give up electrons and go into solution as ions with a charge, in other words they are oxidized.  For different metals, the tendency to do this may be stronger or weaker.  When metals with different tendencies are placed in the same electrolyte, the ions of one metal will be oxidized and the ions of the other metal that have made there way into the solution will be reduced.  This causes an imbalance in the charge on each of the conducting metals, which is the basis of how a battery works.  Different combinations of metals will produce different voltages.  In the case of our zinc copper battery this should be about 1.1 volts. 

 

Now for the fun:



Items you will need: (in parenthesis are the specific brands which I used)

Pennies or other copper or copper plated coins or disks (U.S. pennies)
Zinc plated washers or other zinc or zinc plated disks (heavy dipped galvanized washers)
Vinegar (Heinz brand white vinegar)
Table salt or sodium chloride (Morton brand table salt)
Measuring cup
Measuring spoon
Mixing spoon
Cup to mix the electrolyte
Scissors
Piece of paper (20lb bond white copy paper)
Pencil
Rubber gloves (recommended as best practice)
Goggles (recommended as best practice)
Meter
Red light emitting diode (3mm high brightness red LED rated for 20mA current)
 

The gloves and goggles are recommended as a best practice, but there is nothing particularly dangerous about this experiment.

 

Start by tracing eight or ten discs on the paper.



Next cut out those discs



Next measure out one quarter cup of vinegar and pour it into your mixing bowl



To this add one teaspoon of table salt



mix the salt into the vinegar so that it dissolves and then dunk the paper discs that you cut out into this solution and leave them to soak thoroughly. 



Now we are ready to make a simple battery cell.  Place one zinc washer down and remove one of the paper discs from the solution of salt and vinegar and lay it on top of the washer.



On top of this place a penny.  You have just created a simple cell of your battery.

Take your meter, set it to measure a small voltage of around a volt or so, if you are unsure how to do this check your meter's manual.  Then touch the positive lead to the zinc washer and the negative lead to the penny.



You should see the meter or number on a digital display indicate the presence of voltage.



I usually find about .8 Volts or so from these types of cells, but your results may vary a bit.  The voltage is not high enough to light the LED at this point, but we can stack several of these cells, and when we do, the voltages will add.  This is said to be connecting the cells in series.  For example, a typical car battery consists of six cells in series, with each of those cells providing about 2 Volts for a total of 12. 

Make several more cells just as we did the first one by laying a soaked paper disc on top of a washer, and a penny on top of that.  Measure each one to see that it is working properly.  If you have no voltage, check to ensure that the paper prevents the penny and washer from directly touching each other, and that the paper disc is thoroughly soaked through.
 


Once you have a bunch of working cells, you can stack one on top of the other.  Do not put a paper disc between them when you stack them.



I stacked about six of the cells together in this example.

Next measure the voltage of the stack by setting your meter to read a voltage between 2 and 7 volts for a stack of six, or adjust to measure up to about 1.1 Volts for each cell you have stacked.  Touch the positive lead of the meter to the very bottom zinc washer, and the negative lead to the top copper penny. 



As long as your measurement is about 3V or more it should be sufficient to light a red light emitting diode, or LED.  My red LED actually only requires about 1.7 volts to light, and if you were to connect it to a power supply or battery which could keep the voltage at 3V across its leads, it would burn out.  In our case, our coin battery will only be able to supply about 5mA or so of current, so the voltage will drop to the voltage of the LED at this current, which is about 1.7V or so.  Have a look at your LED.



The longer lead is generally the positive lead.  Bend the leads such that you can contact the positive lead to the bottom zinc washer on your stack of cells, and the negative lead to the top penny.  You should see your LED light up.  If it does not, try reversing the leads so that the longer lead is on the penny, as I have seen a few with longer negative leads.



You should see your LED glowing red as in this photo.

When you take your battery apart you will likely notice that the surface of the zinc washers where the paper electrolyte soaked disc was touching it have turned black.



This is from the oxidized Zinc compounds formed as the Zinc corrodes as part of the reaction.  This is the 'cost' of the energy you have extracted from the battery.  If you were to leave the led connected, the reaction would eventually consume all of the zinc plating. 

Hopefully you have had fun trying or reading about this experiment.  This document was created by me, and you may use, copy, edit, or distribute this material freely.   Richard Hagen, Chicago, Il, USA







« Last Edit: March 30, 2012, 02:25:12 AM by richhagen »
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dinges

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Re: Coin Battery
« Reply #1 on: March 30, 2012, 06:02:11 AM »
Funny, I did exactly the same experiment when I was about that age (though without help from dad).

Just like you, I cut up paper (coffee filters) and used small copper coins and cut-out zinc discs. It worked very nice.

Unlike you, I didn't use safety gear.... no glasses, no gloves ;-)

I built different versions though, consisting of much larger copper and zinc plates (about 30x80 mm) with a pointy end. Used both potatos as electrolyte and glasses of salt water. Both worked fine, good enough to light a red LED.

I recall even taking it to school and the physics teacher being pleasantly surprized. He was one of those really enthusiast teachers who, as you were leaving class and asked him how they determined the absolute zero-temperature (0 K), would spend his entire lunch break explaining it. And about half the class *voluntarily* sacrificing its lunchbreak too to hear about it. Ah. Memories.

Anyway, it's a good demonstration of basic principles of physics and chemistry (redox reactions). We throw about terms about Li-ion, NiMH, etc..... but this is the basics of it all. And though I know *how* it works, it still seems almost magical when you sit back and admire it.

...and they say there are people who don't like physics and chemistry.... ?!

Some other simple projects I recall are simple generators and motors (using a some copper wire, a cork as rotor and an anemic horseshoe magnet), a crystal radio set (using OA81 germanium diode), small rockets made from aluminium foil and matches, dust explosions in a tin jar with milk powder, ....

Come to think of it, I'm still playing with exactly the same stuff now, 25 years later..... :D
« Last Edit: March 30, 2012, 06:04:59 AM by dinges »
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richhagen

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Re: Coin Battery
« Reply #2 on: March 30, 2012, 06:28:48 AM »
Peter you've given me some ideas for the weekend . . . .  Yes, fun stuff. I find that even as an adult I always have my hands onto some project or other involving basic chemistry.  When I did this with my son I did not have the safety gear, but I figured for a tutorial that might be used by a teacher or two, I ought to try and demonstrate it the 'correct' way.  The zinc and copper and their salts are not that hazardous, and the electrolyte is only a bit acidic being buffered by the acetic acid, but if you try it with different metals or electrolytes, you might get to something slightly more hazardous.  I used to electroplate all sorts of stuff, actually I can't believe my parents let me do some of the science and electronic stuff I did when I was a kid, those fly back transformers could generate a bit of potential.   I probably got a pretty good dose of x-rays a time or two as well.  Rich
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