Home-made battery

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The other day my four year old son brought me a hammered flat piece of raw copper his grandfather gave him and asked what we could make with it. I suggested a battery and showed him how we could stack it with paper soaked in salt water and a knockout from an electrical box, then measure the current on a meter.

After that he wanted to make a battery strong enough to light a light. We made a lab notebook and tried several different electrode materials and electrolyte compositions before settling on copper/zinc and water, salt, vinegar, and a few drops of bleach. We used newspaper for the electrode separator. Pencil lead (graphite) gives more voltage than copper, but less current. The bleach triples the closed-circuit current of a cell. I don't fully understand the chemistry.

This battery is built on a plastic ice cube tray with 14 gauge copper wire and galvanized screws from the hardware store. Screws have more surface area than nails. There are four cells. It puts out over three volts open circuit and about 2ma thru the led. We let it run overnight. In the morning it was dim but still working.

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Jim Rees