How to Charge a Capacitor

by J.T. Barett

    A capacitor is an electronic component that stores electric charge. Used in most types of circuits, capacitors act as electrical reservoirs, dampers and frequency filters. Unlike batteries, which also store electricity, capacitors can charge and discharge an almost unlimited number of times. You can learn a great deal about capacitor behavior by connecting it to a simple battery circuit. Measuring the current with a pocket digital multimeter will show the charging process. To limit the current, use a 100-ohm resistor as part of your charging circuit, a switch and a 9-V battery for a safe source of electrical charge.

    Step 1

    Snap the 9-V battery into the clip.

    Step 2

    Turn on the multimeter, and turn its setting knob to a DC current range of about 200 to 400 milliamps.

    Step 3

    Connect one lead of the .1-microfarad capacitor to a jumper lead. Connect the other end of the jumper to one lead of the 100-ohm resistor. Connect a second jumper to the resistor's free lead. Connect the free end of the second jumper to one of the battery clip's bare wire ends. Attach a third jumper to the other battery clip wire.

    Step 4

    Connect the free end of the third jumper to the bare metal end of one of the multimeter's test leads. Attach the end of a fourth jumper to the end of the other multimeter test lead.

    Step 5

    Clip the free end of the fourth jumper to one of the switch's terminals. Connect a fifth jumper to the remaining switch terminal. Attach the jumper's other end to the unconnected capacitor lead.

    Step 6

    Press the switch. The meter display increases to about 100 milliamps, then gradually decreases to zero. When the meter reads zero, the capacitor is fully charged.

    Step 7

    Remove the battery from the clip. Connect both ends of a fifth jumper wire to the bare clips of the battery connector -- not the battery. Press the switch again. The meter display jumps from zero to about 100 milliamps again, then settles to zero. This indicates that the capacitor has discharged.

    Tips

    • In this circuit, charging the capacitor takes current from the battery. Although you can repeat the process hundreds of times, eventually it will drain the battery.
    • Try charging and discharging capacitors of different values with this circuit. Capacitors with capacitance values much less than 1 microfarad charge quickly; those with large values take longer. Electrolytic and tantalum capacitors are polarized with a positive and negative lead. If you use one in a circuit, make sure you connect its positive lead to the positive battery terminal. In this circuit, the red battery clip wire is positive, and the black wire is negative.
    • Current readings on the multimeter may be positive or negative, depending on how you connect the meter probes and whether the capacitor is charging or discharging. The numbers for charging will be opposite to those for discharging, as the current reverses direction. For example, if you see positive numbers as the capacitor charges, the readings will be negative when it discharges.

    Warnings

    • A capacitor charged to beyond its rated voltage will leak, burst or explode. Always use a capacitor with a voltage rating greater than the circuit's voltage.
    • Although you can safely handle this capacitor when it's fully charged, exercise caution when handling charged capacitors from other circuits. Capacitors can retain a charge for long periods of time; handling them can give you an electric shock if the circuit is over 50 V.

    Required Items

    • 9-V battery snap clip
    • 9-V battery
    • .1-microfarad, 100-V capacitor
    • Set of 24-inch jumper leads
    • 100-ohm, 1/4-Watt resistor
    • Digital multimeter
    • SPST pushbutton switch

    About the Author

    Chicago native J.T. Barett has a Bachelor of Science in physics from Northeastern Illinois University and has been writing since 1991. He has contributed to "Foresight Update," a nanotechnology newsletter from the Foresight Institute. He also contributed to the book, "Nanotechnology: Molecular Speculations on Global Abundance."

    Photo Credits

    • Hemera Technologies/PhotoObjects.net/Getty Images