Experiment 5: Let’s Make a Battery

Chapter Experiment 5: Let’s Make a Battery

Make Electronics Book Learning by Discovery
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Make Electronics Book Learning by Discovery

  • Experiment 5: Let’s Make a BatteryChapter 132Experiment 5: Let’s Make a BatteryLong ago, before web surfing, file sharing, or cell phones, kids were so horribly deprived that they tried to amuse themselves with kitchen-table experiments such as making a primitive battery by pushing a nail and a penny into a lemon. Hard to believe, perhaps, but true!This is seriously old-school—but I want you to try it anyway, because anyone who wants to get a feel for electricity should see how easy it is to extract it from everyday objects around us. Plus, if you use enough lemons, you just might generate enough voltage to power an LED.The basic components of a battery are two metal electrodes immersed in an electrolyte. I won’t define these terms here (they’re explained in the following section “Theory: The nature of electricity”). Right now all you need to know is that lemon juice will be your electrolyte, and copper and zinc will be your elec-trodes. A penny provides the necessary copper, as long as it is fairly new and shiny. Pennies aren’t solid copper anymore, but they are still copper-plated, which is good enough. To find some metallic zinc, you will have to make a trip to a hardware store, where you should ask for roofing nails. The nails are zinc-plated to prevent them from rusting. Small metal brackets or mending plates also are usually zinc-plated. They should have a slightly dull, silvery look. If they have a mirror-bright finish, they’re more likely to be nickel-plated.Cut a lemon in half, set your multimeter so that it can measure up to 2 volts DC, and hold one probe against a penny while you hold the other probe against a roofing nail (or other zinc-plated object). Now force the penny and the nail into the exposed juicy interior of the lemon, as close to each other as possible, but not actually touching. You should find that your meter detects between 0.8 volts and 1 volt.You can experiment with different items and liquids to see which works best. Immersing your nail and penny in lemon juice that you have squeezed into a shot glass or egg cup may enhance the efficiency of your battery, although you’ll have a harder time holding everything in place. Grapefruit juice and vin-egar will work as substitutes for lemon juice.To drive a typical LED, you need more than 1 volt. How to generate the extra electrical pressure? By putting batteries in series, of course. In other words, more lemons! (Or more shot glasses or egg cups.) You’ll also need lengths of wire to connect multiple electrodes, and this may entail skipping ahead to 54,Chapter 2, where I describe how to strip insulation from hookup wire. Figures 1-71 and 1-72 show the configuration.If you set things up carefully, making sure than none of the electrodes are touching, you may be able to illuminate your LED with two or three lemon-juice batteries in series. (Some LEDs are more sensitive to very low currents than others. Later in the book I’ll be talking about very-low-current LEDs. If you want your lemon-juice battery to have the best chance of working, you can search online for low-current LEDs and buy a couple.)Figure 1-71. A three-lemon battery. Don’t be too disappointed if the LED fails to light up. The lemons have a high electri-cal resistance, so they can’t deliver much current, especially through the relatively small surface area of the nails and the pennies. However, the lemon battery does generate voltage that you can measure with your meter.Figure 1-72. Bottled lemon juice seems to work just as well as fresh lemon juice. I cut the bottoms off three paper cups, inserted a galvanized bracket into each, and used heavyweight stranded copper wire to make the positive electrodes