5 Easy Steps to Test Capacitors with a Multimeter

A multimeter is a versatile tool that can be used to test a variety of electrical components, including capacitors. Capacitors are used to store electrical energy and are found in a wide range of electronic devices. Testing a capacitor with a multimeter is a relatively simple process, but it is important to follow the correct steps to ensure accurate results. Before starting, discharge the capacitor to avoid an electrical shock

The diode setting can be used to check for a short circuit in a capacitor. Connect the positive probe of the multimeter to the positive terminal of the capacitor and the negative probe to the negative terminal. A short circuit will be indicated by a reading of zero ohms.

Capacitance mode on the multimeter gives capacitance readings if the capacitor is good. If the capacitor is bad, the multimeter will display “OL” meaning “open loop” and indicate no connection or an infinite value.

Setting the Multimeter to Capacitance Mode

To accurately test a capacitor using a multimeter, it is essential to set the device to the appropriate mode for measuring capacitance. Different multimeters may have slightly different procedures for setting the capacitance mode, but here’s a general guide:

Select the Capacitance Range: Most multimeters have a rotary dial or a push-button to select the measurement range. Look for the range that is appropriate for the capacitor you are testing. For example, if you are testing a capacitor with a capacitance of 10 μF, select the range of 100 μF or higher.
Set the Multimeter to Capacitance Mode: Multimeters typically have a function selector switch or a push-button to choose the measurement mode. Locate the setting labeled “Capacitance” (usually denoted by the symbol “F” or “C”).
Connect the Test Leads: Connect the black test lead to the COM (common) terminal on the multimeter and the red test lead to the terminal designated for capacitance measurement.

Additional Tips for Setting Capacitance Mode

If the multimeter has an autoranging feature, it will automatically select the appropriate capacitance range and mode.
Consult the multimeter’s user manual for specific instructions on setting the capacitance mode.
Before testing a capacitor, it is good practice to discharge it by shorting its terminals with an insulated tool.

Capacitance Ranges for Different Types of Capacitors

The appropriate capacitance range to select depends on the type of capacitor being tested. Here’s a table for your reference:

Capacitor Type	Typical Capacitance Range
Ceramic	1 pF – 1 μF
Electrolytic	1 μF – 10,000 μF
Film	1 nF – 100 μF
Tantalum	1 μF – 100 μF

Determining Capacitance Value

To determine the capacitance value of a capacitor, follow these steps:

Set the multimeter to the capacitance measurement mode.
Connect the positive test lead to the positive terminal of the capacitor and the negative test lead to the negative terminal.
Read the capacitance value displayed on the multimeter.
If the capacitance value is very small or very large, the multimeter may not be able to measure it accurately. In this case, you can use an external capacitor tester.
The capacitance value of a capacitor is measured in farads (F). However, capacitors often have very small capacitance values, so they are typically measured in microfarads (µF), nanofarads (nF), or picofarads (pF).

Capacitance Table

Capacitance Range	Units
1 – 999.99 µF	µF
0.001 – 999.9 nF	nF
0.001 – 999.9 pF	pF

Discharging Capacitors Safely

Before testing a capacitor with a multimeter, it is crucial to discharge it properly to prevent electrical shock. Here are the steps to discharge a capacitor safely:

1. Identify the Capacitor

Locate the capacitor you wish to discharge. It will usually have a cylindrical or rectangular shape with two terminals.

2. Gather Necessary Materials

You will need an insulated screwdriver, a pair of insulated pliers, and a discharge resistor (if available).

3. Short the Terminals

With the screwdriver or pliers, briefly touch the two terminals of the capacitor together. This will discharge the capacitor through the resistance of the tools.

4. Check for Discharge

Using a multimeter set to the voltage range of the capacitor, connect the probes to the terminals. If the voltage reading is near zero, the capacitor is discharged.

5. Use a Discharge Resistor (Optional)

If a discharge resistor is available, connect it across the capacitor terminals for a few minutes before shorting them. This provides a more controlled discharge path.

6. Ground the Capacitor

Connect a wire from one of the capacitor terminals to a grounded metal surface, such as a water pipe or an electrical outlet cover plate.

7. Discharge Through a Resistor

Connect a resistor of appropriate wattage and resistance (typically 100 ohms or higher) across the capacitor terminals. Leave it connected for a while to ensure complete discharge.

8. Double Check and Insulate

After discharging, wait a few minutes and re-check the voltage using a multimeter. Cover the terminals with insulating tape or caps to prevent accidental contact.

Capacitor Type	Discharge Method
Electrolytic	Short terminals and wait (no resistor required)
Ceramic, Film, Tantalum	Short terminals using screwdriver or pliers
High-Voltage	Use discharge resistor and ground

Capacitor Discharge

Before testing a capacitor, it’s crucial to discharge it. Always wear proper safety gear and use a discharge tool or a resistor to drain the stored energy. Failure to discharge the capacitor can result in electric shock or damage to the multimeter.

Capacitance Measurement

Set the multimeter to the capacitance measurement range, typically denoted by the “F” symbol. Connect the positive lead to the positive terminal of the capacitor and the negative lead to the negative terminal. The multimeter will display the capacitance value in farads (F).

ESR Measurement

Some multimeters can measure the equivalent series resistance (ESR) of a capacitor. ESR is an important parameter that affects the capacitor’s performance and lifespan. Set the multimeter to the ESR measurement range, connect the probes to the capacitor terminals, and read the displayed ESR value.

Leakage Current Test

Connect the capacitor in series with a high-value resistor (e.g., 1 MΩ) and a voltage source. Measure the voltage across the resistor using a multimeter set to the millivolt range. The leakage current can be calculated using Ohm’s law: I = V/R.

Polarity Check

For electrolytic capacitors, it’s essential to check the polarity before testing. Connect the positive lead of the multimeter to the positive terminal of the capacitor and the negative lead to the negative terminal. If the polarity is incorrect, the multimeter will display a negative capacitance value.

Troubleshooting Capacitor Issues

Open Capacitor

An open capacitor will have infinite resistance and zero capacitance. The multimeter will display “OL” or a very high resistance value.

Shorted Capacitor

A shorted capacitor will have very low resistance and high capacitance. The multimeter will display a very low resistance value or “0L”.

Capacitance Drift

Capacitance drift indicates a change in the capacitor’s capacitance value over time. The multimeter can be used to monitor capacitance changes under different conditions (e.g., temperature, voltage).

Leakage Current Exceeds Specifications

Excessive leakage current can lead to capacitor failure. The multimeter can be used to measure leakage current and compare it to the manufacturer’s specifications.

Polarity Reversed

For electrolytic capacitors, reversing the polarity can damage the capacitor. The multimeter can be used to check the polarity and ensure it is correct.

Interpreting Multimeter Readings

10. Measurement Scales

Multimeters offer various measurement scales for capacitors, typically ranging from nanofarads (nF) to microfarads (µF). Choose the appropriate scale based on the capacitor’s expected capacitance. For example, if testing a capacitor with a capacitance of 100 µF, select the µF scale for accurate readings.

Capacitance Range	Measurement Scale
0.1 pF – 1 nF	pF
1 nF – 1 µF	nF
1 µF – 100 µF	µF

How to Use a Multimeter to Test a Capacitor

1. Set your multimeter to the capacitance range.

2. Connect the positive lead of the multimeter to one lead of the capacitor and the negative lead to the other lead.

3. The multimeter will display the capacitance of the capacitor in farads (F).

4. If the capacitor is working properly, the capacitance reading should be within the tolerance range specified by the manufacturer.