How to Charge a Capacitor

By Kim Lewis

A capacitor usually consists of two conductors placed close to each other, separated by an insulator. It stores electrical charge in units that are called a farad. Common capacitor values typically range from picofarads to nanofarads to microfarads. To charge a capacitor, you need to wire a resistor or test light between the battery and the capacitor. To measure the voltage of the capacitor before, during, and after discharging, use a multimeter.

Things You'll Need

  • Battery
  • Switch
  • Capacitor
  • Resistor or test light
  • Multimeter
  • Wire

Step 1

Connect one end of the battery to the switch. If desired you can use a battery holder to make connecting the wiring easier. Make sure the switch is open -- in the off position.

Step 2

Attach a resistor or test light to the other end of the switch.

Step 3

Secure one end of a capacitor to the resistor or test light. Wire the other end of the capacitor to the unoccupied terminal of the battery holder.

Step 4

Set the multimeter to its voltage reading setting. Place one lead across one end of the capacitor and the other lead across the other end of the capacitor. You may need to find it necessary to use extra wires to hold the leads in place.

Step 5

Place a battery inside the battery holder, and close the switch. Observe the values on the voltmeter. The charge on the capacitor should be approximately equal to that of the voltage from the power.

Step 6

Discharge the capacitor quickly by replacing the battery with a wire. Do not touch the capacitor directly. Again, observe the values on the voltmeter. The voltage will decrease to zero.

Tips & Warnings

  • When wiring the circuit, be sure to observe polarity if you are using an electrolytic or other polarized capacitor. The positive terminal of the capacitor must be connected to the positive terminal of the battery, and the negative terminal of the capacitor must be connected to the negative terminal of the battery.
  • Capacitors can retain electrical charge for long periods of time even when they are not directly connected to a power source, so use extreme caution when handling one.
  • High voltage capacitors found in electronics such as television sets, camera flashes, and radios, for example, may contain large amounts of voltage that may be lethal.