Introduction: Light an LED With Dirt
This was an experiment that I had fun with! Perhaps you might find it fun to replicate?
I've been intrigued by the so called "Earth Battery" for a long time. To be a true Earth Battery, rather than simply a Galvanic Battery, the device must actually be buried in the Earth, to benefit from Telluric Currents. In the past, I experimented with driving copper pipes and zinc plated rods into the ground as electrodes. This works, but I never developed it into an implementation capable of practical use.
The experiment documented in this article, stemmed from an idea that electrodes could be embedded in potted plant soil forming a galvanic battery. It would be charged by the plant being watered and fed. Based on the results, I think with further development the idea could have merit.
With 5 cells connected in series, I got a maximum voltage of 4.3 V, and a maximum momentary short circuit current of 3 - 4 mA. I was able to dimly light an LED for tens of minutes.
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Step 1: Prepare the Plates
Cut five each zinc and copper pieces 100 mm X 20 mm using scissors or metal shears.
Step 2: Make the Enclosure Sides
Cut four craft sticks to 100 mm in length after cutting off the rounded end. Use a strip of clear tape on one side to fasten the sticks together in pairs as seen in the photo. These will be the two long sides of the enclosure.
Cut 10 pieces @ 20 mm, these will be the spacers. After cutting off the rounded end of 4 more sticks, tape them together in pairs as before. Using a stick on edge as a gap gauge (see photo), glue five 20 mm spacers across each pair of sticks with super glue. Cut off the excess length to complete the short sides, leaving a stick thickness overhang on each end.
Step 3: Laminate the Outside Plates
Using double stick tape, laminate a copper plate onto the inside of one long side. Laminate a zinc plate onto the inside of the other long side.
Step 4: Assemble the Sides
Using super glue at the corners, bond the sides together forming a rectangle. Apply clear tape around the outside corners to hold it together until the glue cures.
Solder a wire to each plate as seen in the photo. The copper plate is the positive terminal, the zinc plate is the negative terminal.
Step 5: Laminate the Interior Plates
Laminate the remaining copper and zinc plates together with double sided tape so that each plate has a copper side and a zinc side.
Cut a small notch out of each copper side top center as seen in the photo. Bridge the two sides with solder in the notch. This creates the series connection of the five cells.
Step 6: Make the Base
Align seven craft sticks edge to edge as seen in the photo, and laminate them together with clear tape on both sides.
Step 7: Complete the Assembly
Apply a bead of hot glue to the bottom edge of the sides assembly and press it down on the base. Then apply a bead of hot glue around the inside and outside where the sides meet the base.
Apply hot glue into the slots for each interior plate on at a time, and slide the plate into the slots quickly while the glue is molten. Push it down firmly against the base. Make sure to face the plates all in the same direction!
Once the plates are all glued in, coat the spacers between the plates with hot glue.
Step 8: Prepare the Electrolyte & Fill the Cells
Mix 1/2 cup of debris free moist soil with 1 tablespoon of baking soda. Make sure the baking soda fully incorporates with the soil. Baking soda makes the soil more alkaline and helps the ions bridge the plates which increases current. Carefully fill the cells with the electrolyte mixture packing it in firmly. Screed the top level making sure that the top edges of the plates are exposed.
Step 9: Light an LED
Solder the short leg of the LED to the negative wire (zinc plate). Make a small loop in the positive wire and tin it with solder. When you want to power the LED, slip the loop over the long leg of the LED.
Step 10: Final Thoughts
As the electrolyte dries out, moistening it with tap water can help rejuvenate it. The electrolyte can be replaced if necessary. As can be seen in the photo, an oxide layer forms on the zinc plates during use.
Ideally the enclosure would be made out of plastic. A non conductive enclosure would eliminate the resistive short circuit paths that occur when any bare wood becomes saturated with moisture from the cells. I would have liked to create a purpose designed 3D printed part, but I don't have access to a printer.
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