Make a Flashlight for Pennies

 Weekend Project

I wanted to see if I could make a flashlight out of pennies. Since pennies after 1982 are mostly copper coated zinc they have the potential of making a battery. 

What you need:

•  Pennies
•  Cardboard, or cloth (Cardboard works longer 2 days vs  8 hrs with cloth)
•  Sand paper (electric sander - best, belt sander -  dangerous.)
•  LED (light emitting diode)
•  Acid (lemon juice, or vinegar both work and are safe)
•  Electric tape (duck tape works too, scotch tape - may  be frustrating)
•  Time 

Copper Side

Zinc Side

The first step is to sand down one side of the penny.  So that no one accuses you of defacing the money it is best to use the tails side, but ultimately does not matter. 

I did not have the patience to sand these down by hand.  I placed them close together on a strip of gorilla tape wrapped backwards around a board then used an electric sander.  Cuts through copper like butter!

The first time I did this project I used thick cardboard and the flashlights stayed lit for almost 2 days.  

I also did an experiment with fabric using an old cotton t-shirt.  Surprisingly this created more voltage by .3 v, but also lasted only about 6 hours in the end because it dried faster.  I would recommend leaning toward materials more like cardboard for longer power time. 

If you are using heavy cardboard I recommend soaking it in the acid for about 30 min prior to assembly. 

Stack the pennies all the same way (all copper side up and zinc side down, or vice versa, but not alternating) with the cardboard or cloth between each.  Attach an LED with the positive terminal on the zinc face and negative on the copper face. 

Wrap this contraption tightly with tape and you have a flashlight!

Using cloth I was able to tape the pennies together first then soak up lemon juice by dipping the finished contraption in the juice to activate it. 

If it does not light up.

•  try reversing the terminals on your LED.
•  make sure there the cardboard or cloth does not stick  out so far the touch each other and short the circuit.  
•  check your LED to make sure it works
•  check the connections
•  use a different acid
•  use different insulation material

The longest I have had one of these last is 2 days.  Most seem to last at least several hours and each cell seems to provide about 1.5 v and .30 milliamps. 

My highest voltage was 1.978 v

Not very successful experiment.

Above, I attempted to insulate a bolt with electrical tape and then space the pennies with washers and used cotton material.  It provided a sad 1.4 volts and only lasted 2 hrs.

Here are three different colors.  One made with vinegar, and two with lemon juice.  All were using thick cardboard soaked for 30 min.  

Vinegar was the small red light.  It lasted almost 2 days and only stopped cause it dried out. 

The green and yellow lasted about 24 hours.