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How Capacitors Function and Their Key Applications

Author: The Engineering MindsetTime: 2024-01-06 22:45:02

Table of Contents

What is a Capacitor and How Does it Work?

A capacitor is an electrical component that stores electric charge. It works by having two conductive metal plates, typically made from aluminum, separated by a dielectric insulating material such as ceramic. When connected to a battery or power source, electrons from the negative terminal flow onto one of the capacitor plates, causing a negative charge buildup. The other plate loses some electrons and develops a positive charge. An electric field forms between the two oppositely charged plates, allowing the capacitor to store energy.

A capacitor is analogous to a water tank installed on a pipe. Just like the water tank stores water and releases it to smooth out interruptions in flow, a capacitor stores electric charge and releases it to smooth out interruptions in electricity flow. This allows circuits containing capacitors to continue functioning during temporary power losses or dips.

Capacitor Definition and Function

A capacitor is a passive electronic component that stores electric charge. Its main function is to store energy in an electric field created between a pair of conductors on either side of an insulating material. It essentially acts like a tiny rechargeable battery, allowing circuits to function during short power interruptions.

Capacitor Charge and Discharge Process

When first connected to a power source, current flows to the capacitor as electric charge accumulates on the plates. The insulating material prevents the charges from neutralizing. Once the capacitor voltage equals the voltage of the source, current stops flowing. The capacitor remains charged until connected to a load or shorted. Then the stored charge discharges rapidly to power the load.

Measuring Capacitor Voltage

Because capacitors store electric charge, they exhibit a voltage potential between their two plates. This voltage can be measured with a multimeter set to the DC voltage function, with the positive lead on the capacitor's positive terminal and the negative lead on the negative terminal.

Identifying Different Types of Capacitors

Capacitors come in many shapes and sizes. But the most common types found on circuit boards look like small plastic cylinders with two protruding leads, marked with their capacitance value. Sometimes the negative lead is indicated by a stripe on the side. Larger capacitors used for power applications can be much bigger, with substantial mounting hardware for connecting to induction motors or electrical panels.

By reading the labeling on a capacitor, you can determine its capacitance in farads as well as its maximum working voltage before breakdown. This helps identify the proper capacitor for different applications and circuit positions.

Appearance of Capacitors on Circuit Boards

The capacitors most often seen on printed circuit boards and electronic devices have a basic cylindrical appearance with two wire leads extruding from the bottom. They might be standing upright or laying horizontally against the board. Color coding and stripe patterns help identify polarity.

Larger Capacitor Variants and Their Uses

Very large capacitors are used for motor run applications, power factor correction, and high current filtering tasks. They come in large cylindrical or rectangular metal cans that have substantial mounting points for physical and electrical connection. Their size helps them store much more energy.

Key Capacitor Parameters - Capacitance and Voltage

The two key ratings listed on a capacitor that determine its functionality are capacitance and working voltage. Capacitance, measured in farads, indicates how much charge can be stored. Voltage rating gives the maximum potential difference the unit can withstand before failure.

Typical capacitors have capacitances from picofarads to thousands of microfarads. Minimum working voltages range from a few volts to hundreds of volts. Choosing appropriate ratings allows capacitors to perform their energy storage duties without damage.

Capacitance Units

A farad is the base unit of capacitance, defined as 1 coulomb of charge stored per 1 volt of electric potential. Due to its large scale, capacitors for electronics use are rated in microfarads (μF), nanofarads (nF), or picofarads (pF). Reading the labeling gives the capacitance value.

Maximum Voltage Rating

This rating indicates the highest operating voltage that can be applied before the capacitor electrically breaks down and fails. Exceeding this rating risks permanent damage and even explosion. Similar to current rating for resistors, the voltage rating provides guidance for proper capacitor selection.

Why Use Capacitors?

Capacitors serve several key functions that make them indispensable components of modern electrical systems and electronics:

  • Store energy and release it during power interruptions to smooth supply

  • Correct power factor issues in AC power systems

  • Filter ripple voltage from AC to DC converters

Power Factor Correction

Inductive motors and devices lower electrical power factor, wasting energy. Capacitor banks provide reactive power to cancel out inductive reactance. This brings current and voltage back into phase to restore power factor towards unity.

Smoothing AC to DC Power Conversion

Connecting a capacitor in parallel with the output of an AC to DC converter smooths ripple voltage by providing current during the valleys between rectified sine wave peaks. This stabilizes the DC output.

Safely Measuring Capacitor Values

It is important to properly discharge capacitors before handling to avoid electrical shock. Once discharged to a safe voltage, capacitance and leakage current can be reliably measured.

A multimeter capable of capacitance measurement is extremely useful for testing capacitors to detect damage or check if their values match ratings. However, the first step is always verifying any residual charge has decayed to a low safe level.

Checking Residual Voltage Before Handling

An apparently disconnected capacitor can retain hazardous voltage. Use a multimeter to measure voltage across the terminals. If more than a few millivolts, discharge by connecting a resistor across the capacitor. Measure again to confirm it is safe prior to direct handling.

Measuring Capacitance

Set a multimeter to capacitance function, usually denoted by the symbol C or value readout of nF or μF. Attach meter test leads to capacitor terminals - positive to positive, negative to negative. The capacitance value in farads will display after a short measurement delay. Compare to expected rating.

Conclusion and Further Learning

A capacitor is like a tiny rechargeable battery that rapidly stores and releases energy to enable uninterrupted operation of electronics. Identifying capacitors and understanding their charge/discharge behavior, key ratings, and measurement enables proper circuit design and analysis.

For more information about capacitors, take a look at these educational engineering resources:


Q: What are the main functions of a capacitor?
A: The key functions of a capacitor are to store electric charge for release when needed to smooth power interruptions, and provide power factor correction in AC circuits.

Q: Where are capacitors commonly used?
A: Capacitors are used on almost every circuit board as well as in larger applications like induction motors, ceiling fans, air conditioning units, and for power factor correction in buildings.

Q: How does a capacitor work?
A: A capacitor works by building up separated charges on two conductive plates, creating an electric field. This charge can power a circuit when released.

Q: Why do capacitors explode if you exceed their voltage rating?
A: Exceeding a capacitor's maximum rated voltage causes dielectric breakdown, resulting in arcing currents between the plates that damage the capacitor.

Q: How do you discharge a capacitor safely?
A: To safely discharge a charged capacitor, connect its terminals momentarily to a resistor while monitoring the voltage until it drops to a low and safe millivolt range.

Q: What are the main capacitor parameters to look for?
A: The two key capacitor parameters are capacitance (Farads) determining charge capacity, and maximum rated voltage determining the highest voltage it can handle.

Q: How do you measure capacitance?
A: To measure capacitance, use a multimeter on the capacitance setting, connecting red lead to positive capacitor terminal and black lead to negative.

Q: Why do capacitors help when converting AC to DC?
A: When rectifying AC to DC, capacitors smooth the conversion by filling in power gaps between AC current peaks, providing a more consistent DC output.

Q: What does power factor correction mean?
A: Power factor correction brings current and voltage sine waves back into phase alignment in AC circuits for more efficient power transfer.

Q: Are capacitors safe to handle?
A: Capacitors can hold dangerous residual voltage so should always be carefully discharged before handling to prevent electric shocks.