OPERATIONAL SAFTEY How to test a capacitor?

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Engineers need to monitor the component health of a circuit. Capacitors exhibit a shorter lifespan. They are cheap and easily available in the market, making it easier for engineers to replace them. This article explains how to test a capacitor with a multimeter.

In electronic circuits, maintaining component health is essential for preventing failures and ensuring system reliability. Capacitors, often subject to wear and tear, require frequent testing due to their relatively short lifespan. Their affordability and availability make replacement straightforward when issues arise. This guide outlines the process for testing capacitors using a multimeter, offering practical advice to diagnose and address potential faults promptly. Regular examination helps avert dangerous failures and supports continuous, safe operation of electronic devices.

Faulty capacitors

Whenever a capacitor deviates from its normal operation, it becomes faulty. It may start to function as an open circuit—none of the components connected to the capacitor function. PCBs do not operate. In some extreme cases, a faulty capacitor behaves like a short circuit. It may deteriorate to the point of no return—it simply blows! Such a situation is not safe. Hence, capacitors must be checked regularly for safety and uninterrupted service.

Visual testing

There are various ways to judge if a capacitor has become faulty, even before testing it with a multimeter. This method is called visual inspection of the capacitor.

Value change: The value of the capacitor changes during the operation. It is one of the first indicators of a faulty operation.

Bulging: The head (top surface) of a capacitor bulges out or takes a different shape. It is a sign of overheating.

Leakage: The visual leakage test is for polarized electrolytic capacitors. The electrolytic solution leaks from the capacitor. This shows that the capacitor is subject to undesirable overvoltage.

Discoloration: Capacitors show discoloration in certain areas. Burn marks start to appear on the body. It is a serious sign of overheating or electric arc generation.

Things you need for capacitor testing

To test a capacitor, you need the following things:

• 1. Multimeter: A multimeter is a measuring device that measures voltage, resistance, capacitance, and other electrical parameters.

• 2. Battery: Take a 9-10 V battery.

• 3. Wires: Take connector probes for the multimeter and jumper wires for the capacitor. All red wires represent the positive terminal, and black wires represent the negative terminal.

• 4. Protective gear: Use sunglasses and gloves for protection.

• 5. Isolated discharged capacitor: Capacitors must be removed from a PCB, circuit, or device. A soldering iron can safely remove them from circuits. Even when they are out of their original assembly, capacitors contain stored energy. It is important to discharge any capacitors before the testing process begins. The discharge process must be initiated on a disconnected capacitor.

Capacitors can be easily discharged through a high-wattage resistor, discharge pen, or insulated screwdriver. The method is simple. You just have to touch the positive terminals of the discharge pen to the positive terminal of the capacitor and vice versa. However, the process may result in some sparks. It is critical to wear protective gear.

expert RIPPLE CURRENT

Do you know the ripple current in your capacitor?

How to test a capacitor with a multimeter?

For the question of how to test a capacitor with a multimeter, the answer is to run three critical tests. There are three simple multimeter-based tests to assess the capacitor health.

• Capacitance test

• Resistance test

• Voltage test

Capacitance Test

The capacitance test aims to measure capacitance. The video serves as a tutorial on how to test a capacitor with a multimeter.

Step 1: Check the capacitance value of the capacitor. Note it down. Let us suppose 10 microfarads.

Step 2: Set capacitance mode on the multimeter.

The symbol “C” on the multimeter stands for capacitance mode. Set the multimeter to C. These settings measure the capacitance.

Step 3: Set the multimeter to a higher capacitance value, such as 20 microfarads.

Step 4: Connect the red probe of the multimeter to the positive terminal of the capacitor.

Step 5: Connect the black probe of the multimeter to the negative terminal of the capacitor.

Step 6: Note down the final multimeter reading.

• Healthy capacitor: The multimeter reading shows the actual capacitance value near 10 microfarads. Calibration of +/-10% is acceptable. In general practice, +/-2% shows that the capacitor is highly operational.

• Shorted capacitor: The reading is significantly higher than the original capacitance.

• Open capacitor: The reading is significantly low or near the over limit (OL).

Resistance Test

Ideally, a capacitor should show infinite resistance on a measuring instrument.

Step 1: Set the multimeter settings to measure the resistance.

Step 2: Set the multimeter to 2 Mega Ohms.

Step 3: Place the connecting probes of the multimeter on the capacitor terminals.

In case of a polarized capacitor, such as an electrolytic capacitor, the red (positive) probe must be placed on the positive terminal of the capacitor. The black (negative) probe must be placed on the negative terminal of the capacitor. Any wrong connection would result in a spark or capacitor burst.

Step 4: Note down the multimeter reading.

• Healthy capacitor: The multimeter reading slowly rises from zero to infinity.

• Shorted capacitor: The multimeter reading shows a fixed low resistance value.

• Open capacitor: The multimeter reading directly shows an infinity value.

Voltage Test

The voltage test measures the voltage of the battery connected to the capacitor. It uses jumper probes for a direct connection between the battery and the capacitor:

Step 1: Set the multimeter settings to measure the voltage.

Step 2: Take a battery. Note down its voltage. It is a 10 V battery.

Step 3: Connect the positive terminal of the battery to the positive terminal of the capacitor using a red jumper probe.

Step 4: Connect the negative terminal of the battery to the negative terminal of the capacitor using a black jumper probe.

Step 5: Set the multimeter needle to a value higher than 10 V, which is 20 V.

Step 6: Connect the positive red probe to the plus sign at the bottom left of the multimeter.

Step 7: Connect the negative black probe to the minus sign at the bottom left of the multimeter.

Step 8: Use the other end of the probe, incoming from the multimeter, to touch the capacitor terminals.

The red probe should touch the red terminal of the capacitor, and the black probe should touch the black terminal of the capacitor.

Step 9: Note down the multimeter readings.

The multimeter reading must display the actual battery voltage (10 V). +/- 2 V is also acceptable. An accurate voltage value shows that the capacitor is healthy.

Precautions

If you wonder how to test a capacitor with a multimeter is an easy question, you are mistaken. Playing with wires and components calls for extra safety. Professionals can run such tests on the basis of their knowledge and expertise. Certain precautions are listed below:

• Isolate the capacitor from the circuit, PCB, or device.

• Discharge the capacitor before the test.

• Use industrial-grade, quality equipment.

• Conduct tests in a safe environment free of water and other electronic devices.

• Monitor the voltage.

• Use shock-resistant gloves to avoid direct contact.

• Wear sunglasses to safeguard your eyes from electric arcs.

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