Build Instructions

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• 1

  Remove copper coating from back of pennies

  Use regular sandpaper to remove the thin copper coating from three or four US pennies, minted after 1982. Newer pennies are made from pure zinc with a thin copper coating.

  There's about seven or eight minutes of sanding between the photo above and below.

  It took us about half an hour per penny. After three pennies it was getting dark, and we were out of patience, and expendable thumb nails.

  We heard somewhere that it's even harder to remove the copper on the front (heads) than the back (tails). Tails was hard enough.

  We tried both coarse and fine grit, but didn't see much difference.

  There must be a better way!

• 2

  Make a separator for each cell

  We used AeroPress coffee filters for separators.

  Folded in half three times they become about the size of a penny.

  Trim off the excess paper.

• 3

  Soak the separators in household vinegar

  We used pure household vinegar (5% acetic acid) as electrolyte. It is common to add some table salt (sodium chloride) to improve conductivity, and perhaps to mitigate partial passivation of the zinc anode. To keep the chemistry as simple as possible, we went with pure vinegar.

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