Battery Equivalents and Replacements

How to Test a Capacitor With a Multimeter

Capacitors are fundamental components in the vast world of electronics, functioning as reservoirs that store and release electrical energy. These components are crucial for various applications, ranging from smoothing out electrical fluctuations in power supplies to enabling the functionality of dynamic electronic circuits like oscillators and filters.

The versatility of capacitors also extends to energy storage, where they can quickly charge and discharge, making them ideal for flash photography, electric vehicles, and as supplementary storage in renewable energy systems.

Published: June 20, 2024.

capacitor

In everyday devices such as televisions, air conditioners, and smartphones, capacitors help manage voltage and power flow, ensuring stable operation and prolonging the lifespan of the device.

They are also instrumental in signal processing, serving as filters that allow certain frequencies to pass while blocking others, which is essential in audio and radio frequency equipment.

Understanding how to test a capacitor's functionality with a multimeter is not just a skill but a necessity for anyone involved in the maintenance, repair, or design of electronic systems.

Understanding Capacitors and Multimeters

What is a Capacitor?

A capacitor is an electronic component that stores electrical energy in an electric field, created between two conductive plates separated by an insulating material called the dielectric.

When voltage is applied across the plates, an electric field develops, and charge accumulates until the capacitor reaches its capacity.

The capability of a capacitor to store charge is measured in farads (F), although most common capacitors have values in the microfarad (μF) or picofarad (pF) range.

Capacitors come in various forms, including electrolytic, which are typically used for higher capacitance requirements such as in power supply circuits; ceramic, known for their small physical size and stability, making them suitable for high-frequency applications; and film capacitors, which offer superior tolerance and are used in audio circuits and signal processing.

Types of Multimeters and Their Functions

A multimeter is a versatile instrument used to measure electrical parameters such as voltage, current, and resistance. It can also be used to test the functionality of various components, including capacitors.

Multimeters come in two main types: analog and digital.

  • Analog Multimeters: These use a moving coil meter and a needle to display readings. They are appreciated for their ability to track changing trends over time and are particularly useful in situations where a quick response is needed. However, they may require careful handling and interpretation, as reading the scale accurately can be challenging.
  • Digital Multimeters (DMMs): These provide readings in numerical form, making them easier to read and more precise than their analog counterparts. Digital multimeters often come with additional features such as the ability to measure capacitance, frequency, and temperature. They may also include specific settings for testing diodes and transistors, making them an indispensable tool for both professional technicians and hobbyists.

fluke 117 digital multimeter 2

Safety Precautions

Essential Safety Tips Before Testing Capacitors

Testing capacitors, particularly in circuits that handle high voltages, demands adherence to strict safety protocols to prevent injuries or equipment damage. Here are some essential safety tips:

  • Disconnect Power Sources: Before beginning any tests, ensure that the device or circuit is completely powered down and disconnected from any power source. This step is critical to prevent any electrical shock or damage to the multimeter and the capacitor.
  • Discharge the Capacitor: Capacitors can retain a charge even when the power is off. Use a resistor to safely discharge the capacitor. Connect a resistor across the capacitor's terminals for a few seconds to allow the charge to safely dissipate. Choose a resistor with a high enough wattage rating to handle the discharge without overheating.
  • Inspect for Damage: Visually inspect the capacitor for any signs of damage, such as bulging, leakage, or burn marks. Damaged capacitors can be hazardous and should be handled with care.
  • Use Insulated Tools: Always use tools with insulated handles to avoid direct contact with charged components.
  • Wear Safety Gear: Wear protective eyewear and gloves as an extra precaution, especially when handling capacitors from high-voltage circuits.

Note: Whenever we talk about safety on Battery Equivalents, we often get comments via email how these safety precautions are too much in everyday life.

Personally, when you accidentally touch a fully charged capacitor of any "decent" voltage, you will also wear gloves whenever approaching anything that may still have some residue charge left ... been there, done that :)

Handling Charged Capacitors

Handling charged capacitors requires extra caution due to the potential for sudden discharge. Here are some guidelines:

  • Never Touch the Terminals: Avoid direct contact with the capacitor terminals even if it is presumed to be discharged. Use tools to bridge the terminals when necessary.
     
    Use the Correct Technique to Discharge: Always use a resistor rather than a direct short-circuit method with a wire or tool, as this can cause a violent and dangerous discharge.
  • Store Safely: If a capacitor needs to be removed and stored, ensure it is fully discharged. Keep it in a clearly marked container to avoid accidental handling.

Preparing for the Test

Tools and Materials Needed

To test a capacitor effectively, you will need the following tools and materials:

  • Digital Multimeter: Choose a multimeter with a capacitance measuring feature or one that can test for continuity.
  • Resistors: Have resistors on hand for safely discharging capacitors. 
  • Insulated Pliers and Screwdrivers: For safe handling and disassembly of electronic circuits.
  • Protective Gear: Safety glasses and gloves to protect against accidental discharges.

Setting Up Your Multimeter

Setting up your multimeter correctly is essential for obtaining accurate readings. Here’s how to prepare your multimeter for testing a capacitor:

  • Select the Appropriate Function: If your multimeter has a capacitance measurement mode, select this function. If not, set it to the resistance or continuity test mode for basic functionality checks.
  • Zero Adjustment: For analog multimeters, ensure the needle reads zero before beginning. For digital multimeters, confirm that it’s calibrated and reading accurately.
  • Test Leads: Connect the test leads to the appropriate ports on the multimeter. Typically, the black lead goes into the common (COM) port, and the red lead goes into the port marked for voltage, resistance, or capacitance, depending on your measurement.
  • Safety Check: Double-check that the multimeter and leads are in good condition and rated for the voltages and currents you anticipate measuring.

With these preparations complete, you're ready to begin the actual testing of the capacitor, ensuring you approach each step with safety and precision.

Testing the Capacitor

Step-by-Step Guide to Testing a Capacitor With a Multimeter

Testing a capacitor to determine its health or measure its capacitance involves careful setup and execution. Here’s how to perform the test:

  • Ensure Safety and Preparation: Confirm that the capacitor is fully discharged and the device or circuit is powered down.
  • Connect the Multimeter: Attach the test leads of the multimeter to the terminals of the capacitor. Ensure a good contact is made to get accurate readings.
  • Set the Multimeter:

• If measuring capacitance, set the multimeter to the capacitance measurement mode. This is usually indicated by a 'Cap' or a capacitor symbol on the dial.

• For a basic functionality check, set it to the ohm meter setting to measure resistance or use the continuity setting to check if the capacitor is open or shorted.

  • Read the Multimeter:

• For capacitance measurements, the display should show the capacitance value of the capacitor, which you can compare against the manufacturer's specifications.

• For resistance checks, observe the behavior of the reading. A healthy capacitor should initially show low resistance, then gradually move towards infinity (open circuit) as it charges from the multimeter's internal battery.

  • Record Your Findings: Note down the readings for future reference or further analysis.

Interpreting the Results

  • Capacitance Value: If the capacitance value displayed is within the tolerance range specified for the capacitor (usually ±5% to ±20% of the marked value), the capacitor is likely in good condition.
  • Resistance Check: A slowly increasing resistance value that approaches infinity is normal, while a constant low resistance indicates a shorted capacitor. A constant high resistance (open circuit) might suggest the capacitor is non-functional or broken internally.

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Troubleshooting Common Issues

What to Do if Your Capacitor Fails the Test

If the capacitor does not pass the tests:

  • Check for Visible Damage: If there’s visible damage like bulging, leakage, or burn marks, replace the capacitor.
  • Retest with a New Capacitor: Sometimes, replacing the suspect capacitor with a new one is the fastest way to confirm if the original was faulty.

Tips for Troubleshooting Multimeter Errors

Sometimes, the issue may lie not with the capacitor but with the testing setup or the multimeter itself:

  • Check Battery and Connections: Ensure the multimeter’s battery is charged and that all connections are secure and clean. Poor connections can result in inaccurate readings.
  • Calibrate the Multimeter: If possible, calibrate your multimeter or compare it against another device to ensure it is providing accurate readings.
  • Check the Test Leads: Damaged or worn-out test leads can cause errors. Test them for continuity and replace if necessary.
  • Consult the Manual: Refer to the multimeter’s manual for specific error codes or troubleshooting tips related to your model.

Maintenance Tips for Capacitors

Regular Maintenance Practices for Capacitors

  • Maintaining capacitors is essential to ensure the longevity and reliability of electronic devices. Here are some regular maintenance practices:
  • Visual Inspection: Regularly check capacitors for signs of wear, such as bulging, leakage, or discoloration. These are indicators of potential failure and should be addressed immediately.
  • Environment Control: Ensure that capacitors are operating in a suitable environment with controlled temperature and humidity levels. Excessive heat or moisture can degrade capacitor materials over time.
  • Testing Capacitance: Periodically test the capacitance of capacitors as part of routine maintenance checks, especially in critical applications. This helps in detecting any significant changes that might indicate degradation.
  • Clean Contacts: Keep the capacitor’s contacts and terminals clean from dust and corrosion, which can affect performance and lead to poor conductivity.

When to Replace Your Capacitors

Knowing when to replace capacitors can prevent failures in electronic circuits:

  • Age: Consider replacing electrolytic capacitors after 5 to 10 years, as they tend to degrade due to the drying out of their electrolytic substance.
  • Performance Drop: Replace capacitors if tests show that their capacitance levels have dropped significantly below their rated values.
  • After a Fault: If a device experiences a power surge or a similar fault, check and replace any capacitors that may have been stressed beyond their limits.
  • Upgrade: When upgrading circuit components or the entire system, assess whether existing capacitors meet the new specifications and replace them if necessary.

Recommended Multimeters

Here is a short list of some of the best multimeters on the market.

Note: Amazon affiliate links open in the new windows.

  • Fluke 117 Digital Multimeter: Ideal for professional use, offering high accuracy, durability, and all necessary safety features.
  • Klein Tools MM600: A robust option for DIYers and professionals alike, known for its ruggedness and versatility.
  • Amprobe AM-530: A great value-for-money choice for hobbyists and professionals, providing reliable measurements and several advanced features.
  • Extech EX330: Perfect for beginners, featuring an easy-to-use interface with essential functions and an affordable price point.

Of course, there are other great units on the market - feel free to search for the digital multimeter (Amazon link, opens in the new window) and with fast delivery, you can have your new multimeter rather quickly.

fluke 117 digital multimeter 1


Capacitors are critical components in electronic circuits, storing and managing electrical energy.

Testing capacitors with a multimeter involves preparing properly, setting up the device, conducting tests, and interpreting the results to assess health and performance - it may sound complicated since it involves several important steps, but it is not after some practice.

Since capacitors may store enough energy at high enough voltage to shake a human being seriously, be careful when working with them - better safe than sorry.