A Battery That Makes Cents
|Time Required||Very Short (≤ 1 day)|
|Prerequisites||To do this project, you will need an adult to help you use a multimeter. Science Buddies has a reference, How to Use a Multimeter, that will teach you how to use one.|
|Material Availability||Readily available|
|Cost||Very Low (under $20)|
AbstractBatteries are expensive, but you can make one for exactly 24 cents! In this experiment, you will make your own voltaic pile using pennies and nickels. How many coins in the pile will make the most electricity?
In this experiment, you will make a simple battery out of coins and test if the number of coins in the pile will affect the amount of electricity produced.
Sabine De Brabandere, PhD, and Sara Agee, PhD, Science Buddies
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Last edit date: 2017-07-28
You might think that batteries are a modern invention, but batteries were one of the first ways of making electricity. Alessandro Volta discovered the first electric battery in 1800. He made a giant stack of alternating layers of zinc, blotting paper soaked in salt water, and silver. This early design for a battery became known as the voltaic pile.
Figure 1. This image shows the structure of a voltaic pile, which is the first design of a battery that's used to make electricity. It was discovered by Alessandro Volta in 1800. (HowStuffWorks.com, 2007.)
How does a voltaic pile make electricity? The key to electricity is the movement of particles carrying electric charge. In a voltaic pile, these particles move from one metal to the other through a solution called the electrolyte. An electrolyte is a liquid that contains particles carrying charge. Dissolved salt is an example of a good electrolyte. The charged particles in the electrolyte react with the metals, causing an electrochemical reaction, a special kind of chemical reaction that makes electrons. As electrons are particles that carry electric charge, making these electrons all move in the same direction will create a electric current or electricity. You can read more about the basics of electricity in the Science Buddies Electricity, Magnetism, & Electromagnetism Tutorial.
The two types of metals in a voltaic pile are called electrodes. As the types of metal are different, one metal will like to give off free electrons, the other will be more eager to receive electrons. This creates an electrical potential difference, also called voltage between the two types of metals. One metal becomes positively charged (the positive electrode) and the other becomes negatively charged (the negative electrode). This voltage causes electrons to move, creating an electrical current, and then you have electricity!
In this experiment, you will make your own version of the voltaic pile using two different types of coins (two different kinds of metal) and a salt-vinegar solution (the electrolyte). The metal in the coins will react with the electrolyte. As the two metals are different, one metal will like to give electrons to the other, creating electricity. How will different numbers of coins affect the amount of electricity produced? To test this, you will make piles with different numbers of coins and measuring the voltage (measured in Volt) and current (measured in Ampere) produced.
Terms and Concepts
To do this type of experiment, you should know what the following terms mean. Have an adult help you search the Internet or take you to your local library to find out more!
- Electric charge
- Electrochemical reaction
- What materials can a battery be made out of?
- Why is it important for the materials to be arranged in alternating layers?
- What does the electrolyte solution do?
- Will more layers make a more or less powerful homemade battery?
An introduction to the voltaic pile and its history can be found here:
MIT Special Collections (n.d.). The Voltaic Pile. Retrieved June 17, 2015, from https://libraries.mit.edu/collections/vail-collection/topics/electricity/the-voltaic-pile/
- For an overview of what batteries are try this video:
Mocomi Kids. (2015). How Do Batteries Work? Retrieved June 17, 2015, from https://www.youtube.com/watch?v=KkRwuM4S8BQ
- A more in-depth explanation of the chemistry behind voltaic cells (the more modern version of a voltaic pile) can be heard in this musical video:
Edmonds. (2011, March 12). The Simple Voltaic Cell Circuit Song. Retrieved June 17, 2015, from https://www.youtube.com/watch?v=gNnJ9t3HDQs
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Materials and Equipment
- Vinegar (any kind, 1/4 C.)
- Salt (1 Tbsp.)
- Small bowl or glass
- Pennies (4)
- Nickels (4)
- Dish soap
- Aluminum foil (small strip)
- Paper towels (2)
- Small plate (ceramic, plastic, or StyrofoamTM; not paper or metal)
- Digital multimeter (any kind that reads mA and mV), available from suppliers like Jameco Electronics and Amazon
- Lab notebook
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- In your lab notebook, make table like the Table 1. You will write down your measurements in this table.
|Number of pennies||Number of nickels||Voltage (V)||Current (mA)|
- In a small bowl or glass, mix together 1/4 C. of vinegar (electrolyte) and 1 Tbsp. of salt (ions). Stir well.
- Gather some pennies and nickels, wash with a mild detergent (like dish soap), and dry. This is just a preliminary step to remove dirt and grime.
- Using scissors, cut a strip of aluminum foil, 2 cm x 8 cm. Fold lengthwise in three as shown in Figure 2. Aluminum foil is a good electrical conductor. It will help create good electrical contact with the bottom penny of your pile.
Figure 2. An aluminum strip is folded in three lengthwise. First cut out the strip, then fold the edges in and last press them down.
- Using scissors, cut up a paper towel into small squares, each a little over 2 cm x 2 cm.
- Place a dry paper towel on a plate as shown in Figure 3. You now have all the materials to start building.
Figure 3. A few pennies and nickels, small paper-towel squares, a vinegar-salt solution, and an aluminum strip is all you need to create a coin battery.
- Place the aluminum strip in the middle of your plate. You will build your battery on top. This strip will make it easier to connect the multimeter later.
- Start building your stack:
- Put down a penny on the aluminum foil.
- Soak a paper towel square in the vinegar-salt solution. The square should be wet throughout but not dripping.
- Place a square of vinegar-soaked paper towel on top of the penny as shown in Figure 4.
Figure 4. Start building your battery by placing a penny on the aluminum strip, followed by a soaked paper-towel square.
- Add a nickel on top of the square paper towel, as shown in Figure 5. This is a tiny battery. You will add 2 more coins before measuring.
Figure 5. One battery cell consists of a penny, a soaked paper-towel square and a nickel on top.
- To add more coins, put down a penny on the top nickel.
- Repeat steps b.–d. You now have a stack of four coins (alternating pennies, wet paper towel pieces, and nickels), ending with a nickel on top.
- Important: do not let the paper towel squares droop over the edges of the coins and touch each other. This will create a short circuit and prevent your battery from working. If necessary, use scissors to trim the corners of the paper towel squares so they do not hang down and touch the paper towel below them.
- Important: paper towel squares should be wet but not dripping. Dripping electrolyte can create a short circuit. If necessary, press out excess liquid from the paper towel squares by placing them between your thumb and a finger.
- Make a measurement. See the Science Buddies reference How to Use a Multimeter if you need help.
- Connect the probes (also called leads) of the multimeter to the two ends of the battery by placing one probe tip on aluminum foil strip at the bottom of the stack and the other to the nickel on the top of the stack. Figure 6 shows the setup.
- Measure the voltage produced by your battery: set the multimeter to measure DC voltage (direct current) and select volts (V) as shown in Figure 6. Push down on the multimeter probe tips to make good electrical contact. Write down the your measured value (number only, not the sign) in the table like Table 1. Note positive or negative measured values are both fine. You are interested in the number value without the sign (see also step d.) Consult the Frequently Asked Questions for more advice.
Figure 6. To measure the voltage produced by your cell, place one multimeter lead on the aluminum foil strip and the other on the top nickel.
- Measure the current produced by your battery: set the multimeter to measure current, select milliamps (mA) and record the current in your data table right away (the current may begin to drop slightly as the battery begins to drain). The multimeter setting to measure current is shown in Figure 7. Consult the Frequently Asked Questions for more advice.
Figure 7. Set the multimeter to measure in mA to measure the current produced by your cell. Note the sign of your measurement indicates the direction of the current.
- Note: You might encounter a negative reading like the one in Figure 7. The sign informs you about the direction of the current. You do not need to pay attention to the sign for this project. You are interested in the magnitude ( 0.118 mA in case of the reading shown in Figure 7).
- Add a penny, soaked paper towel square and nickel to the stack and measure again. As you add to your stack, one important rule is to always start with a penny and end in a nickel, so the number of layers of pennies and nickels will always match. Why do you think this is necessary?
- Repeat step 9 for your new stack. Do not forget to record the number of pennies, the number of nickels and the measured voltage and current in your data table.
- Repeat steps 10 and 11 one more time. You now have a stack containing 4 pennies and 4 nickels, like the stack shown in Figure 8.
Figure 8. This coin battery uses 4 pennies and 4 nickels.
- You can keep repeating steps 10 and 11, building batteries consisting of more and more coins.
- Analyze your data.
- Your data table is now complete. Can you observe a trend?
- Making graphs may help you visualize your data. If you need help creating graphs, try the Create a Graph website.
- Make a bar graph of the voltage (vertical axes) versus the number pennies (horizontal axes). Do not forget to label the axes and add a title. An example showing only one measurement is shown in Figure 9. Your graphs will show more measurements.
Figure 9. A bar graph showing one measurement: the voltage for voltaic pile consisting of 2 pennies and 2 nickels.
- Make a bar graph of the current (vertical axes) versus the number pennies (horizontal axes).
- How do voltage and current change when you add more coins? Are your results consistent with what you expected?
- Repeat the entire experiment (Steps 2–14) twice more. Start all over again building a new battery from pennies and nickels. Scientists always perform several measurements to confirm their results. Do you get the same measurements each time? Do you see the same trend?
- Now you are ready to create your science fair display board! If you need help making your display board, a downloadable display board template for this project is available for purchase below. The template provides step-by-step guidance for creating all the usual sections of a display board: title, abstract, background information, question, hypothesis, variables, results, conclusions, and acknowledgements.
Downloadable display board template - only $1.99
For troubleshooting tips, please read our FAQ: A Battery That Makes Cents.
If you like this project, you might enjoy exploring these related careers:
- Try connecting an LED to your battery with copper wire or aluminum paper strips. How many coins do you need to light the light? You can test different LEDs to see if they need the same number of coins to light up. (LEDs only pass current in one direction, so be sure you have it oriented correctly.) Note on copper wire: Be sure the wire is NOT enameled, or it will not work! Enameled copper wire can be used if you first strip the insulation off. This can be done with sandpaper, as explained in this Wire Stripping Tutorial.
Compare different coin combinations to see which ones work and which ones don't:
- Penny - Dime
- Nickel - Dime
- Nickel - Quarter
- Penny - Quarter
Try other electrolyte solutions to see which ones work and which ones don't:
- Plain water
- Salt water
- Lemon juice
- Soda water
- Try making batteries out of other things, like potatoes or fruits. Try the Science Buddies experiment Potato Battery: How to Turn Produce into Veggie Power! for more ideas!
Frequently Asked Questions (FAQ)
- The bigger the contact area between the moist paper towels and the coins, the bigger the current will be. Keep pushing down on the top coin with your probe, as you are measuring, to ensure good contact over the entire surface.
- Just like a battery you buy in the store, this battery drains and can run out. Mark down the measurement right as you start measuring, before it starts draining.
- The pennies will corrode as they produce electricity. Cleaning off this corrosion and using new damp pieces of paper towel will help revive your battery.
- Check if pushing down on the multimeter probes provides a better reading. Pushing on the probes can help make a firm contact. This contact is needed to allow electricity to flow. You can also move around the probe on the top nickel and see if a different spot on the nickel provides a better contact.
- Check carefully to be sure no paper towel squares droop over the edges of the coins and touch other paper towels or other coins. Touching paper towels will create a short circuit in your battery and prevent your battery from working. If necessary, use scissors to trim the corners of the paper towel squares so they do not hang down and touch the paper towels below them.
- Ensure the paper towel squares are very damp, but are not leaking over the edge. Dripping electrolyte can create a short circuit. If necessary, press out excess liquid from the paper towel squares by placing them between your thumb and forefinger. In contrast, dry paper towels are a barrier for the electricity. If they are too dry, dip them in the electrolyte, press out the excess liquid, and try again.
- See if your coins are corroded. You can see corrosion as a buildup of a different color on your coins; if you see some, wash the corrosion off and try again. You can also start with new, clean coins.
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