Introduction: Aluminum Foil Plate Capacitor
This instruction set will teach you how to construct a simple, cheap capacitor quickly and safely. Capacitors have many uses for hobbyists such as in Tesla coils, coil guns, radio transmitters, and filters, but essentially they are just used to store charge. Make sure to read the steps and comments carefully to avoid any personal injury or equipment damage. Building the capacitor itself is easy enough that a beginner could do it, but make sure to practice caution when charging and discharging the capacitor. Those steps should be avoided by anybody without electrical experience. Building the capacitor itself should take no more than 15 minutes, and can go much more quickly with experience, but the charging may take more time. Soon you will have your own homemade capacitor bank to use for one of many future projects. Forget alternative capacitor options, such as disassembling disposable cameras or lugging around huge bottles, you can soon have thin, portable, powerful capacitors at your disposable.
- Heavy Duty Aluminum Foil
- Pair of Scissors
- 3 pages of Printer Paper 8.5x11 in. (21.6x27.9 cm.)
- 3 Electrical Clips
- DC Voltage Source (battery or DC generator)
- 10 Kilo-ohm Resistor
- Heavy Books (anything heavy and flat will do)
Step 1: Measure and Cut the Aluminum Foil.
1. Measure and cut 2 rectangular sections of Aluminum Foil measuring 6.5x10.5 inches (22.9x25.4 cm.)
2. Cut rectangular sections (1.5x5 in., 3.8x12.7 cm.) out of the aluminum sheets so there is a tab (1.5x1.5 in., 3.8x3.8 cm) sticking out of the top left corner of each piece. See above figure for example.
CAUTION: If the aluminum foil sticks outside of the paper (aside from the tabs) it could short your voltage source when you try to charge it!
Step 2: Attach the Sheets.
1. Tape one aluminum sheet on either side of a piece of paper so that the tabs are on opposite sides. See above figure for example.
CAUTION: If the aluminum foil sticks outside of the paper near the opposite plate it could short your voltage source when you try to charge it!
Note: Ensure that the only parts of the aluminum sheets sticking out are the tabs on opposite sides. The reason the sheets are smaller than the paper is so that it doesn’t arc and short the circuit.
Tip: Make sure the aluminum sheets are as aligned as possible on either side of the paper. The more area both sheets share adds to the capacitance, which is a measure of how much charge a capacitor can hold for a given voltage.
Tip: Apply tape liberally so that the aluminum is as flat and close to the paper as possible. The less distance between the sheets adds to capacitance.
Step 3: Enclose the Capacitor.
1. Tape one piece of paper (2 total) over the aluminum sheets on each side to cover all exposed aluminum foil except the tabs sticking out at the top.
Tip: Use tape as liberally as needed. See figure above for finished look.
You have finished construction, now it is time to charge your capacitor!
Step 4: Set Up to Charge.
1. Make sure the DC voltage output is off.
WARNING: If the output is on while you connect the clips, you could shock yourself painfully.
2. Attach electrical clips from the DC voltage source to the capacitor: one clip to a tab and the other to the 10 kOhm Resistor.
CAUTION: If the resistor is not connected in series while charging the capacitor, you could short out your electrical equipment.
3. Attach the third clip from the opposite side of the Resistor to the tab with no clip on it yet.
Note: It doesn’t matter which clip you attach to which tab, as long as both tabs are connected to a clip. See figure above for example.
Note: Make sure the resistor is in series with the capacitor. If the capacitor is intact, there should be no current and the resistor won’t affect the total voltage across the capacitor.
Note: If the capacitor has a short, the Resistor will protect your voltage source from being completely short- circuited.
4. Place the connected capacitor underneath the Heavy Books.
Note: This is done in order to flatten the aluminum sheets together and increase capacitance by decreasing distance between the sheets.
Step 5: Charge the Capacitor.
1. Turn on the voltage source and wait about 30 seconds for the capacitor to fully charge. See above figure for example.
Note: The time you have to wait varies with the capacitance and resistance, so using a smaller resistor will make the wait time significantly less.
Note: The capacitor should reach the value of the input voltage.
CAUTION: Do not exceed 1400 V or the capacitor may ignite.
2. Turn off the output voltage and remove the alligator clips from the tabs.
WARNING: Failure to turn off voltage output could result in a painful shock.
Step 6: Measure the Voltage and Experiment.
1. Set the voltmeter to measure DC voltage and connect one lead to each tab and read the output.
Note: Output voltage should be near input voltage. See figure above for example.
Note: If the output is not near to your input voltage, there is probably a short in the capacitor. Inspect carefully to make sure there is not, but if there is a short, detach the capacitor and try to find where it might be. Make sure the separating piece of paper is completely intact with no holes or tears, as those would short the circuit.
2. Try out different combinations of materials.
Tip: Use wax paper or saran wrap. They have higher dielectric constants so they will store more charge than paper without breaking down, but they require more steps to make because you have to cut them to size.
Note: Make sure that whatever you use has about an inch of margin on all sides around the aluminum foil to avoid a short.
You have finished building your capacitor and it is now ready for use. Any future electrical projects are now yours to complete. You should now have a rectangular, layered piece of paper and foil with tabs of foil protruding from the covering paper sheets. Feel free to test your product out by charging and discharging it, but be sure to practice safety precautions while doing so. Always connect a resistor in series with your capacitor while charging in case it has a short so there will be no damage to your electrical equipment. Now go experiment with different materials and see what you like best!