How to Turn a Potato Into a Battery

Abstract

Imagine telling your friends about your latest science project: using a battery to make a light turn on. You might get some blank stares...sounds a little boring and basic, right? Now tell them you will do it with a potato! Yes, you can actually use fruits and vegetables as part of an electric power source! Batteries power many things around you, including cell phones, wireless video game controllers, and smoke detectors. In this science project, you will learn about the basics of battery science and use potatoes to make a simple battery to power a small light and a buzzer.

Objective

Measure how the voltage and current of potato batteries change when you combine them in series or parallel.

Introduction

Batteries are containers that store energy, which can be used to make electricity. This method of storing energy allows us to make portable electronic devices (imagine what a pain it would be if everything had to be plugged into a wall outlet to work!). There are many different types of batteries, but they all depend on some sort of chemical reaction to generate electricity. The chemical reaction typically occurs between two pieces of metal, called electrodes, and a liquid, called an electrolyte. It turns out that the movement of positive ions through the water inside a potato work pretty well as a galvanic cell, so you just need to add some metal electrodes to a potato, and you have a battery!

Materials and Equipment

Copper electrodes (3)

• Zinc electrodes (3)

• Alligator clip leads (6)

• Digital multimeter with test leads

• Piezoelectric buzzer

• Red light-emitting diode (LED) (3)

• Potatoes (3), any large type like a russet. Make sure your potatoes are fresh. Old, dried out potatoes will not work well.

• Ruler

• Paper towels for cleanup as you prepare the potatoes

• Lab notebook

  Experimental Procedure

• Insert one copper and one zinc electrode into each of the potatoes, as shown in Figure 4. Use a ruler to make sure you space the electrodes the same distance apart and insert them to the same depth in each potato (for example, 2 cm apart and 3 cm deep. The exact distances you pick may depend on the size of your potatoes).

Measure the open-circuit voltage of a single potato battery, as shown in Figure 5. Refer to the Science Buddies resource How to Use a Multimeter if you need help using a multimeter.

1. Set your multimeter dial to measure in the 20 V range.

2. Plug the red multimeter probe into the port labeled VΩmA.

3. Plug the black multimeter probe into the port labeled COM.

4. Use a green alligator clip to connect the black probe to the zinc electrode.

5. Use a red alligator clip to connect the red probe to the copper electrode.

6. Record the voltage in the first row of your data table.

Measure the short-circuit current, as shown in Figure 6.

1. Leave the multimeter probes and alligator clips connected as they are.

2. Change the multimeter dial to measure in the 20 mA range.

3. Quickly record the current in your data table. The current will start to drop as the battery begins to drain.

4. Important: Do not connect the multimeter to regular batteries (for example AA or 9 V) with these settings. Regular batteries can provide much more current than a potato battery, and can damage your multimeter.

5. Test if the potato battery can light up the LED, as shown in Figure 7.

   1. Disconnect the alligator clips from the multimeter probes (leave them connected to the copper and zinc electrodes).

   2. Connect the red alligator clip to the longer lead of the LED.

   3. Connect the green alligator clip to the shorter lead of the LED.

   4. Important: Current can only flow through LEDs in one direction. It is important to connect the copper electrode (positive electrode) to the longer lead of the LED, and the zinc electrode (negative electrode) to the shorter lead. Your LED will never light up if it is connected backwards.

   5. Record in your lab notebook whether or not the LED lights up.

Test if the potato battery can power the buzzer, as shown in Figure 8.

1. Disconnect the alligator clips from the LED.

2. Connect the red alligator clip to the buzzer's positive (red) wire.

3. Connect the black alligator clip to the buzzer's negative (black) wire.

4. Important: The buzzer functions similarly to the LED. It has positive and negative pins, and it will not work at all if it is connected backwards.

5. Record in your lab notebook whether or not you can hear the buzzer.

Now connect two potato batteries in series, as shown in Figure 9, then repeat steps 3–6.

Connect three potato batteries in series, as shown in Figure 10, then repeat steps 3–6.

Copy the data from the first row of your data table (Series - 1 potato) to the fourth row of your data table (Parallel - 1 potato). Remember that you need at least two potatoes to actually make a series or parallel circuit. This just makes it easier to graph your data later.

1. Connect two potato batteries in parallel, as shown in Figure 11, then repeat steps 3–6.

Connect three potato batteries in parallel, as shown in Figure 12, then repeat steps 3–6.

Repeat the entire procedure (steps 1–11) two more times, for a total of three trials. Create a new data table for each trial. Remove and re-insert the electrodes into new locations on the potatoes each time.

1. Analyze your data.

   1. Create a fourth data table for average values. For each configuration (for example, two batteries in series), calculate an average open-circuit voltage and short-circuit current across your three trials. These are the values you will use for your graphs.

   2. Make a line graph of open-circuit voltage vs. number of potatoes. Draw one line for series and one line for parallel. Make sure to include a legend on your graph so you know which is which.

   3. Make a similar graph for short-circuit current.

   4. How do voltage and current change in each graph? Are the lines different for series and parallel connections? Is this what you expected based on your background research?

   5. How much voltage and current does it take to power the LED? Is there a certain voltage or current below which the LED will not turn on?

   6. How much voltage and current does it take to power the buzzer? Is there a certain voltage or current below which the buzzer will not turn on?

2. Cleanup: Dispose of the potatoes in the trash. Do not eat the potatoes after using them for this experiment.

Now that you are done with your project, you might be wondering if you can power something bigger than an LED or a buzzer. Can you use a potato battery to power a lightbulb or charge a phone? There are many videos online claiming that you can. Based on your results, do you think those videos are real?