Homemade batteries are a popular subject with my readers. Making electricity from things you find around the house is a fun project.
There are lots of easy ways to make homemade batteries. Basically, any two different kinds of metal can be placed in a conducting solution and you get a battery. Familiar homemade batteries include sticking copper and zinc strips into a lemon or a potato to make a battery.
One quick battery is made from a soda can, the soda from the can, and some copper.
The photo above shows a battery made by placing a strip of copper and a strip of aluminum into a glass of Coca-Cola (I used the sugar-free cherry flavored variety because that's what I found in the refrigerator).
You can make the aluminum strip by cutting open the can. You will need some sandpaper to sand off the paint and plastic coating from the aluminum before using it. Or you can get strips of aluminum already free of coatings from a hardware store.
You can get copper flashing from a hardware store and cut out a strip of it, or you can use a bunch of copper wire (the more surface area exposed to the liquid, the more electrical current is produced).
The aluminum-copper-coke battery will produce about three quarters of a volt.
Using a zinc strip instead of the aluminum produces a little over a volt in the copper-zinc-coke battery. That zinc should work better than aluminum in a battery is a little surprising, since aluminum is normally more reactive than zinc, but in this cell I suspect the aluminum has an oxide coating that is interfering with the reaction. I have not seen a thorough scientific study of a Coca-Cola copper aluminum battery, and it may be a while before I do.
Another easy battery to make at home is the zinc-air battery. In this battery, the strip of zinc is oxidized by dissolved oxygen in salt water. We used a level tablespoon of salt in a cup of water.
The "batteries" we have shown here are more correctly called "cells". An actual battery is made up of two or more cells.
The zinc-air cell produces about three quarters of a volt. To get higher voltages, which are needed to run things like light emiting diodes (LEDs) or calculators or watches, we connect two or more cells in series to make a battery.
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Two zinc-air cells in series produce about a volt and a half. In the photo above, you can see that this is enough to make a red LED light up. To make it brighter, you can add more cells.
If the LED in your project doesn't light up, try reversing the leads. The diode is a device that only works in one direction. The leads on the diode usually have one lead longer than the other, to make it easy to see which way it is connected. With my diode, the long lead was the one to connect to the copper electrode.
If you don't have a strip of zinc, you can make an aluminum-air battery, as shown in the photo above. It produces a little more than half a volt, so you will need three cells in series to light the LED.
A different chemistry is involved in the copper-zinc-vinegar battery, shown in the photo above. In this battery, the zinc is oxidized by copper ions from the copper strip. In this battery, the copper gradually migrates into the vinegar, and then replaces the zinc at the zinc electrode.
After lighting the LED all night long, you can see a black coating of copper and copper oxide sludge has formed on the zinc.Even though the battery has been lighting the LED all night, it still has a lot of zinc left to keep it lit for several days.
Three of the copper-zinc-coke batteries produce about 3 volts, and can replace the 3 volt lithium battery in this small clock/calendar/calculator. It has been running for days now, and can probably last months. The calculator works, and the alarm chimes play just fine.
