I had fairly good success with the Zinc Air (sort of) battery, so I decided to make something using pennies. Prior to 1981, the U.S. pennies were made of solid copper, but 1981 and after the pennies have been made with zinc and a copper coating.
I got six pennies, three of the solid copper and three of the zinc, and took them outside and sanded them on the walkway cement. I sanded the back side, to get rid of the copper coating and expose the zinc, and to get a smooth surface on the solid copper pennies. I tried a piece of heavy sandpaper and it helped speed up the sanding.
Using some cut up paper towel, I positioned the pennies in a stack so that I had:
Copper, paper towel, zinc, copper, paper towel, zinc, copper, paper towel, zinc
I used two layers of paper towel. This gave me three cells in series. I then clamped the stack together with a plastic spring clamp, and positioned a red LED so that the leads were clamped to the ends, with the cathode or flat spot towards the zinc penny.
I poured out a bottle of 5% white vinegar into the bottle cap and I poured some on the paper towels. The LED lit up bright, but after ten or twenty seconds, went dim. I thought that the spring clamp was too strong, and not enough vinegar was getting into the paper towels. I removed the spring clamp and put a rubber band around the pennies, and poured some more vinegar onto the paper towels. The red LED again lit up, but went dim even quicker. The battery was working, but it just wasn’t working long enough. I tried to get a picture of it but by the time I got the camera focused, the LED had gone dim.
I’ve read that the hydrogen bubbles build up on the plates, and that stops the current from flowing. So I decided I needed a different battery design with the pennies dipped into jars of vinegar, which would allow the bubbles to escape. I got three small plastic ‘custard cups’ and a plastic tube to hold them together. I took the battery stack apart and cleaned off the pennies. I soldered two pairs of the zinc and copper pennies together with two 3 inch lengths of solid copper wire, soldering to the edge to leave the surfaces clean. The remaining pair of pennies each got six inch wire lengths for connecting to the LED.
I positioned the pennies in the cups to make the three cells in series. I filled up each cup with enough vinegar to cover the pennies, and Bingo! The red LED lit up brightly and stayed lit. After awhile the bubbles built up on the zinc pennies, and the LED became a bit dimmer but still stayed lit. I could shake the whole tub and get some of the bubbles off the pennies and the LED would light up brighter for a short while.
After more than thirty hours, the LED is still lit, and the zinc pennies are bubbling vigorously. A little shake gets the LED to light up a bit brighter for awhile. But it’s like the Eveready Bunny, it just keeps going and going.
Update Sat Feb 1 – It’s been 45 hours, and the zinc pennies are still bubbling and the LED is still lit. The vinegar evaporates (or is being converted into hydrogen bubbles) so I added a small amount to each cup to keep the pennies under the solution. Sort of like the lead acid batteries in vehicles: sometimes they need a bit of H2O to keep them running. I bumped into the battery and some of the vinegar spilled out onto the counter, so I retired the experiment.
One thing I’d like to do is triple the number of pennies so that the battery will put out three times as much current. Someone will probably recommend adding a Joule Thief, but I can’t see why I should waste half the power when I can add another cell and get higher voltage with no loss of power.
One thing I’ve noticed is that when I look through the pennies I receive, I seldom find any pennies that are solid copper. I think the copper thieves have removed them, turned them into scrap and sold them. I read an interesting article about how the Gramm Leach Bliley Act allowed the big banks to get into the commodities business, and how they manipulated the metals markets to raise prices. The price of aluminum went up, and other metals did, too. Sounded like the fox was in charge of the chicken house. Here is one article about this. http://www.marketoracle.co.uk/Article43786.html