What we will be creating is a voltaic pile, named for its inventor, Alessandro Volta in 1800. Our pile battery will consist of cells created from a US penny, cardboard, a US nickel, lemon juice, and salt (not shown in images). Another item not shown was a piece of glossy card cut from an advertising mailer. I didn't think of it while shooting the images, but used it to encase the battery and make it fit the flashlight better. I chose coated, glossy card for this as it will not readily absorb our electrolyte.
The lemon juice is an acid which acts as a catalyst to enhance the reaction, to it we add sodium chloride (table salt) to reduce the internal resistance of the battery. We will cut thin cardboard pieces to the size of a penny, soak them in the acidic electrolyte, and sandwich them between nickels and pennies. It just so happens that the 3 AA battery packs common in cheap LED flashlights are just a tiny bit smaller than a US nickel, which is why I chose this arrangement.
For those who want more chemistry information:
A galvanic voltaic cell contains two metals which are dissimilar in electrical potential, separated by a thin barrier. To this cell we then add an electrolyte which causes the electrochemical reaction to occur. The metal contains cations, ions heavy with protons; cations react with water containing anions (electron heavy). While one metal causes the reduction of oxidation in the other, the reaction of anions and cations create an exchange of electrons - an electric current.
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On with the show!
What you need:
- US Pennies (copper plated zinc - we want the copper here)
- US Nickels (25% nickel, 75% copper - we are utilizing the nickel content)
- Lemon juice or another acid such as strong acetic acid for cleaning coffee pots
- Table salt (sodium chloride)
- A sharp knife
- Thin cardboard or similar material
- Electrical tape (vinyl)
- Multimeter or another device to measure output voltage
Note: the number of coins and spacers needed will vary depending on many factors, you will need to adjust them depending on what the output of your cell measures. Just remember they should be dissimilar and alternating. If you are not in the US, check to see what metals your coins are made out of and use two with a different electrical potential such as zinc and copper.
Step 1: Preparing the Barriers
If you're young, clumsy, or for any other reason think you might have problems then please do this with supervision or ask for help. It is far less embarrassing to ask for help than to cut yourself badly and have to explain to a trauma physician how you managed to hurt yourself. Cost of this project will rise exponentially if medical expenses are incurred.
Step 2: Preparing the Battery
Take your cardboard wafers and thoroughly soak them in a solution of lemon juice or other acid with a small amount of sodium chloride mixed in. Begin stacking your cells (nickel, cardboard, penny, cardboard, nickel...) and measure the voltage with a multimeter. Continue building until you reach about 3.5 volts, the equivalent of three 1.25V AA batteries.
If your stack becomes taller than the original battery pack height then clean your coins, try stronger acids, or use thinner barriers. Some experimentation may be necessary.
If you end up with a highly efficient stack which is too short, then simply stack nickels on the anode side until it fits. This will add some resistance, measure final result.
Once you have reached the desired voltage from your battery, wrap it in something non absorbent to keep it contained and stiff. I used a cut piece from a glossy advertising mailer, as mentioned in the introduction. Check to make sure the battery will fit the flashlight and make adjustments as needed. When done, wrap the battery in vinyl electrical tape from top to bottom, leaving only the center of the end coins exposed to make contact inside the flashlight. Check again to ensure everything is still working after assembly.
Remember that the cells will produce less electricity as the electrolyte evaporates. Keep them moist.
Step 3: Conclusion and Results
If you are having problems, make sure you don't have shorts in the cells (coins touching), your electrolyte is conductive and acidic or basic, and that the battery fits properly in the compartment. Check polarity, remember the cathode (-) is the penny side. If you look closely in one of the attached images, you'll see I forgot too. :)
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Remember to vote for this Instructable in the Make It Glow! challenge. We just made something glow (blindingly) with spare change! Also, vote in the Pocket Sized Contest, since it is pocket sized, as is the flashlight, and it uses pocket change. Also entered in the Mad Science Fair.
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