A Practical Guide to Capacitors

Capacitors are essential components in almost every electronic device—from power supplies to motors. This practical guide from JCM Electronics breaks down the different types of capacitors, how they work, how to choose the right one, and how to troubleshoot faulty capacitors.

6 min read
A Practical Guide to Capacitors

Table of Contents

Capacitors are essential components in virtually every electronic circuit. Whether you're working on power supplies, amplifiers, signal processing, or RF applications, the type of capacitor you choose can significantly affect circuit performance.

What Is a Capacitor?

A capacitor is a passive electronic component that stores and releases electrical energy in a circuit. It consists of two conductive plates separated by an insulating material called a dielectric. When voltage is applied, an electric field is created, allowing the capacitor to store energy and release it when needed—ideal for filtering, smoothing, or timing in circuits.

The concept of capacitance was first explored in the 18th century, and the earliest capacitor, known as the Leyden Jar, was invented in 1745 by Pieter van Musschenbroek in the Netherlands. Since then, capacitors have evolved into various types suited for different functions across modern electronics.

What Is Capacitance?

Capacitance is the ability of a capacitor to store electrical charge. It is measured in farads (F), though most practical capacitors are rated in microfarads (µF), nanofarads (nF), or picofarads (pF).

The amount of capacitance depends on:

  • The surface area of the plates – larger area = more capacitance
  • The distance between the plates – smaller gap = more capacitance
  • The type of dielectric material – better dielectric = higher capacitance

In a circuit, higher capacitance allows the capacitor to store more energy, making it useful for applications like energy storage, signal filtering, and power supply smoothing.

AC vs DC Capacitors?

Capacitors are also categorized based on their application in AC (Alternating Current) or DC (Direct Current) circuits:

  • DC Capacitors are used in circuits with a constant polarity, like filtering in power supplies or smoothing voltage in DC electronics.
  • AC Capacitors are specifically designed to handle alternating current and are commonly used in motor run/start applications, power factor correction, and AC signal coupling. These are built to withstand continuous polarity reversal.

Some capacitors, like ceramic or film capacitors, can function in both AC and DC environments depending on their voltage rating and construction. However, electrolytic capacitors are generally DC-only and can be damaged if exposed to AC unless they are specially designed for it (like non-polarized types used in motor start applications).

Different Types of Capacitors

Below is a breakdown of the most common types of capacitors, their features, and typical use cases:

1. Ceramic Capacitors

Most common. Small. Affordable. Versatile.

  • Features: Non-polarized, small size, high-frequency performance
  • Dielectric Material: Ceramic
  • Applications: Decoupling, bypassing, general-purpose use
  • Pros: Low cost, wide range of values, stable at high frequencies
  • Cons: Limited capacitance range, temperature-sensitive (especially Class II/III)

➡ Common types: MLCC (Multilayer Ceramic Capacitors) ➡ Used in: Power rails, microcontrollers, RF circuits, PCBs

2. Electrolytic Capacitors

High capacitance in a compact size – ideal for power applications.

  • Features: Polarized, high capacitance values
  • Dielectric Material: Electrolyte-soaked paper
  • Applications: Power supply filtering, audio circuits, bulk energy storage
  • Pros: High capacitance in small volume
  • Cons: Shorter lifespan, higher ESR, polarity must be observed

➡ Common types: Aluminum Electrolytics, Solid Polymer Electrolytics ➡ Used in: Power supply circuits, amplifiers, DC filtering

3. Tantalum Capacitors

Compact and stable – often used in space-constrained circuits.

  • Features: Polarized, stable over time
  • Dielectric Material: Tantalum pentoxide
  • Applications: Smartphones, laptops, medical devices
  • Pros: Excellent stability, better ESR than aluminum electrolytics
  • Cons: Sensitive to surge current, relatively expensive

➡ Used in: Consumer electronics, tablets, automotive electronics

4. Film Capacitors

Reliable, durable, and precise – perfect for demanding applications.

  • Features: Non-polarized, low ESR and ESL
  • Dielectric Material: Polyester, polypropylene, etc.
  • Applications: Audio systems, power electronics, motor run/start
  • Pros: Very stable, long lifespan, high voltage handling
  • Cons: Larger in size, limited capacitance range

➡ Used in: Industrial equipment, power converters, AC motors

5. Supercapacitors (Ultracapacitors)

Massive capacitance for energy storage.

  • Features: Extremely high capacitance
  • Dielectric Material: Electrochemical double-layer
  • Applications: Backup power, memory protection, regenerative braking
  • Pros: Rapid charge/discharge, high energy density
  • Cons: Lower voltage ratings, more expensive

➡ Used in: Energy storage systems, solar power backup, hybrid vehicles

6. Mica Capacitors

Precision capacitors for high-frequency applications.

  • Features: Non-polarized, very stable
  • Dielectric Material: Mica
  • Applications: RF circuits, military and aerospace
  • Pros: Low loss, high reliability, temperature stability
  • Cons: Higher cost, limited capacitance range

➡ Used in: Radio transmitters, frequency tuning circuits, satellite communication equipment

7. Variable Capacitors

Adjustable capacitance – useful in tuning circuits.

  • Features: Manually or electronically adjustable
  • Applications: Radios, tuners, test equipment
  • Pros: Useful in prototyping and tuning
  • Cons: Mechanical wear over time

➡ Used in: AM/FM radios, communication receivers, signal generators

8. Motor Start and Run Capacitors

Essential for AC motor performance.

Start Capacitors

  • Type: Electrolytic AC-rated capacitor
  • Purpose: Provide a high starting torque by giving a phase shift during startup
  • Features: High capacitance, used only at motor startup, disconnected after a few seconds
  • Cons: Cannot be used continuously, shorter life than run capacitors
  • Used in:
    • Air compressors
    • Air conditioners
    • Refrigeration compressors
    • Pumps
    • Garage door openers

Run Capacitors

  • Type: Polypropylene Film Capacitor (oil-filled or dry)
  • Purpose: Maintain phase shift during motor operation for efficiency and power factor correction
  • Features: Lower capacitance, continuous duty, stable and durable
  • Used in:
    • Ceiling fans
    • HVAC blower motors
    • Washing machines
    • Furnace motors
    • Commercial refrigeration systems

Which Capacitor Should You Use?

✔ Need high-frequency filtering? Go ceramic. ✔ Need bulk power smoothing? Go electrolytic. ✔ Need stable performance in compact designs? Consider tantalum. ✔ Working with precision AC or audio circuits? Film is your friend. ✔ Starting or running motors? Choose the right AC motor capacitor.

Buying and Troubleshooting Capacitors

How to Buy Capacitors: What to Look For

When replacing or selecting a capacitor for your project or repair, here are key factors to consider:

  • Capacitance Value (µF, nF, pF): Match the exact capacitance rating specified in your device or circuit.
  • Voltage Rating (VDC or VAC): Choose a capacitor with an equal or higher voltage rating than your circuit requires. Avoid using underrated voltage capacitors.
  • Type of Capacitor: Determine if you need ceramic, electrolytic, film, etc., based on your application.
  • Polarity: Some capacitors like electrolytic and tantalum are polarized—ensure correct orientation during installation.
  • Tolerance and Temperature Rating: For sensitive circuits, choose capacitors with tighter tolerance and higher temperature ratings (e.g., -40°C to +105°C).
  • Size and Mounting Type: Consider space constraints and whether you need a through-hole or surface-mount type.

How to Tell If a Capacitor Is Bad or Failing

A failing capacitor can disrupt the entire circuit. Look out for these signs:

  • Bulging or Leaking Electrolyte: Most common in electrolytic capacitors
  • Burn Marks or Discoloration: Indicates overheating or damage
  • Equipment Malfunction: Sudden performance issues or failure to start
  • Low Capacitance Reading: Test with a multimeter or capacitance tester
  • No Continuity in Motor Circuits: Indicates a bad start or run capacitor

If you're unsure, remove the capacitor and test it using a digital multimeter with capacitance mode or a dedicated tester.

Capacitor Selection Quick Reference Table

Type Capacitance Range Voltage Range AC/DC Typical Use Case
Ceramic pF to µF Low to Medium Both Filtering, decoupling
Electrolytic µF to mF Low to Medium DC Power supply smoothing
Tantalum µF Low to Medium DC Compact electronics
Film nF to µF Medium to High Both Motors, audio, power electronics
Supercapacitor Farads Low DC Backup power, energy storage
Mica pF to nF High Both RF, precision circuits
Variable Adjustable Low to Medium Both Radio tuning
Start/Run Capacitors µF Medium to High AC HVAC, compressors, motors


⚠️ Safety Tip

Always discharge capacitors before handling. Even small capacitors can retain a charge after power is turned off, which can cause electric shock or damage components.

What Affects Capacitor Lifespan?

Capacitor performance can degrade over time. Key factors that impact lifespan include:

  • Heat Exposure: Higher operating temperatures accelerate aging
  • Voltage Stress: Operating close to or beyond rated voltage shortens life
  • Ripple Current: High ripple current increases internal heating
  • Storage Conditions: Moisture and extreme temperatures can degrade materials

Recommended Tools for Testing Capacitors

  • Digital Multimeter with Capacitance Mode
  • ESR (Equivalent Series Resistance) Meter
  • Dedicated Capacitor Tester

Shop Capacitors at JCM Electronics

We stock a wide range of capacitors—ceramic, electrolytic, film, tantalum, and more—for all your project needs. Browse our catalog today or reach out to our team for expert recommendations.

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