Adam graduated from Virginia Tech in 2005 with a Bachelor's Degree in Technology Education. After college Adam began his teaching career at the Thomas Jefferson High School for Science and Technology. Adam currently teaches courses in Engineering and Energy Systems at TJ.
How to Make a Potato Battery
Engineer Adam Kemp demonstrates how to make a potato battery.
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Adam Kemp: Hi! I am Adam Kemp. Today, we are learning about how to make a battery. In this clip, we are going to take an ordinary household potato and turn it into a voltage source, powerful enough to drive an LED.
To start off, you need to get a regular household potato and cut it in half. Because a household potato is relatively large we do not need the whole thing and we can use the two halves to make two voltage sources. So if you go ahead and cut your potato in half, you will start to notice that they are relatively juicy. I do not think potatoes are known for the juices, but that is exactly what is going to act as the electrolyte we need in order to produce that electron flow between our anode and our cathode. With a potato, the electrolyte consists of phosphoric acid.
In order to produce the anode for our battery, we are going to need a nice shiny penny. If you cannot find a shiny penny, if you take some of the steel wool and gently rub back and forth on the penny, it is going to remove a lot of the oxidation that is going to inhibit producing a nice cathode for our battery. Now, if you take your knife that you used to cut the potato apart and make an incision in one side of the battery, you take your penny and gently insert it into the battery so far that you've got just a little bit of that piece of that penny sticking out. Now, the further you get the penny into the potato, the more contact that the copper has with the phosphoric acid inside the battery.
Next, you are going to produce the cathode by taking the galvanized steel nail and driving it into the other side of the potato. At this point, it is very important that the cathode does not touch the anode. If the two touch together you are going to produce an electric circuit and the battery will not work.
Now, if we take our multimeter and move our range selector to 2 volts range, we will see that we have got a red and a black lead on our multimeter. This indicates which goes to the anode and the cathode. If we attach the black one to the cathode and the red one to the anode, we will see that we are producing a good bit of voltage. In this case we are producing about 0.58 volt. If you drive that zinc a little bit further in, make sure your penny is in there. You should be able to get a little bit more voltage out of it. We have got about 0.2 volts more out of this potato battery. If we think back to when we were illuminating an LED, we were going to need 1.5 volt and about 10 milliamps of current. In order to do that, with a battery that is producing anywhere between 0.5 and 0.75 volts we are going to need a lot more potatoes. Here we have six half potato batteries, then we are going to orient in both, in series and in parallel in order to get enough voltage and current to drive in LED. If we take our multimeter, we can measure the voltages coming out of each battery. If we put the red on the anode and the black on the cathode, we will see that we are getting about 0.63, about 0.58 volt, about 0.65 volt, about 0.63 volt, about 0.62 volts and 0.9 volts, that my good battery. In order to produce the 1.5 volts, it's necessary to illuminate the LED. We are only going to need three of our potato batteries. If we take these three batteries and align them in a series fashion, we are going to produce approximately 1.5 volts and we can measure that with our multimeter. To start off, I am going to take one of my leads and I am going to connect it from the anode to the cathode of the other battery. I am going to follow this step for my third battery. What I am left with is an anode on one battery and a cathode on the other. They are almost oriented in the single foil or line. If I take a final two electrodes, and I'll like to use red and black, black indicating the cathode, red indicating the anode. What I am left with is two leads proper to connect to an LED. Now I can take my multimeter and measure to make sure that I am achieving the required voltage. If we see on the multimeter, we are getting about 1.67 volts, which should be proper in order to illuminate the LED. If you look at an LED, an LED has an indication that tells you which side is the anode and which is the cathode. Normally, if it is the brand-new LED, one leg will be slightly longer than the other leg. The longer leg indicates the anode, while the shorter leg indicates the cathode. On most LEDs, there is also a flat side that looks like a minus sign that indicates the cathode.
If we connect our leads now to our LED, I can see that it's illuminating very dim, but it is illuminating on the VAS. If I show it to the camera, you probably will not see anything. If you want to make it brighter, we have got three extra potato batteries that we can align in parallel with these three batteries in series that will give us the required current to make the LED brighter. In order to do that, I am going to separate these batteries from the series fashion. I am going to split the batteries up into pairs. Each pair of batteries is going to be oriented in parallel. Then we are going to connect them altogether in series. In order to connect two batteries together in parallel, we are going to connect their cathodes to each other and we are going connect their anodes to each other. If we recall the first clip, I have outlined that connecting batteries in parallel does not increase their voltage, it increases their current. So by connecting three pairs of parallel batteries together in series, we are going to increase their voltage and increase their current. Now that we have three pairs of batteries connected in parallel in order to increase the current, which will make the LED brighter, we need to connect these three pairs in series. All we need to do to do that is connect the cathode on one to the anode on the other. Then repeat this step until you have completed connecting the three pairs of batteries in series. What we are left with is only one anode and only one cathode. Now, if we take and connect the LED to our new mega battery and see if it shines any brighter, what I will do is I will flash the LED on and off to see if the camera can see it. As you see the LED is shining a lot brighter than it would have if we only had three batteries in series. So we have increased the voltage by putting the batteries in series and increase the current at the same time by putting them in parallel. Coming up in the next clip is an overview of how to make a lemon battery.