How to Make a Coke Can Capacitor

Materials: Aluminum soda pop can, 1 sheet of letter sized paper, 2" wide clear plastic shipping tape,  glue stick or fast
drying liquid glue, aluminum foil, one self tapping screw (wood or sheet metal is fine), two 6" lengths of insulated stranded
wire, nail to punch hole in can.

1. Strip insulation from wires to expose 1" of bare wire on each end. Fray one end of one wire so the individual strands form
a fan.

2. Fold paper in half, top of paper down to meet bottom. Crease the fold with a smooth hard object to make a sharp crease.

3. Cut a strip of aluminum foil 2" x 8 1/2".  Paste the strip across the middle of the paper. Place it so that the left end is
positioned about 1" from the left side of the paper, and about 1" of foil overlaps right end of paper forming a flap or tab.

4.. Before proceeding with the next steps, understand them.

5. Insulating the foil: Cover the foil completely with one thickness of clear plastic tape.  It's best to run the tape from left to
right, covering the top half of the foil with one strip and the bottom half with another.  It's best not to overlap one taping over
the other, but if you have to, it's preferable to having any aluminum foil exposed. If any part of the foil contacts the can the
capacitor won't work properly. Cut the tape so that the 1"  foil flap is not taped.

6. Wrapping the paper around the can: You should now have the foil covered smoothly with no wrinkles. The only foil
you can touch is the flap. Wrap the paper around your coke can with the foil inside. Start with the end that does not have the
foil flap.  When you bring the two ends of the paper together they will barely overlap forming a tube around the can.
Straighten the edges.  Place small pieces of tape on either side of the foil flap to hold the paper in place.  The paper tube
should fit just tight enough to slide smoothly along the length of the can with no binding and no air space.

7. Forming one terminal: Position the frayed end of the wire under the foil flap and tape it down tight. This forms one
terminal of the capacitor. Cover the entire paper seam and foil flap with a strip of tape.

8. Forming the other terminal:  Wrap an end of the other wire around the screw and insert it into a hole punched the top
of the can.  You can use the bottom of the can but it is curved and harder to work.  Tighten the screw down to form a secure
connection.

Operation: When the paper tube is pulled away from the can and positioned so the aluminum foil is not surrounding any part
of the can, you have zero capacitance.  Slide the tube in so that it starts to cover the can. When the foil reaches a point where
all of the foil is covering a part of the can, capacitance will be approximately 475 pf.



QUESTIONS AND ANSWERS


Q:  I enjoyed your web page on building the coke can capacitor. I just had one question. When I wrap the coke can is the foil flap on the outside, and do I place the wire under the flap on the outside? Sorry I misunderstood the instructions. I interpret it as the flap on the outside of the wrap with the wire under it.   Thank you for your time, consideration, understanding, and patience.

A:  Electrically it doesn't matter. Mechanically, it might matter. If your wire is not very flexible, it's better to tape it onto the outside of the flap.  If you have really flexible wire,  it can be taped inside, where it looks nicer.

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