By Mindy Baca | Updated Aug 30, 2022
A potato clock is a classic demonstration that turns a humble vegetable into a functioning electric clock. By inserting two metals into the potato’s juice, you create a simple galvanic cell that converts chemical energy into electricity. While a single potato only produces about 0.5 V, wiring two cells in series gives you the 1–2 V required to power most LED clocks.
Open the LED clock’s battery compartment and remove the button battery. Note the locations of the positive (+) and negative (−) terminals.
Drive a galvanized (zinc‑coated) nail about an inch deep into each potato. The zinc acts as the anode, where the phosphoric acid in the potato juice oxidizes the metal and releases electrons.
Push a short piece of stripped 12‑gauge copper wire into each potato. The copper serves as the cathode and reacts with the acid, drawing electrons from the anode and producing a flow of current.
Attach the copper wire from one potato to the clock’s positive terminal using a jumper lead with an alligator clip. Connect the galvanized nail in the other potato to the negative terminal.
Use a third set of leads to link the galvanized nail in the first potato to the copper wire in the second potato. This series connection adds the voltage of both cells, giving you the power needed for the LED display.
Once the two cells are wired in series, the LED clock should light up and display the correct time.
Ensure the galvanized nail and copper wire do not touch inside the potato; otherwise the reaction stalls. Roughen the metals with steel wool or sandpaper for a stronger current. Rough, textured nails expose more zinc surface, boosting performance.
Do not consume the potatoes after the experiment. Dispose of them properly.
