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How To Test A Capacitor? Using Various Methods

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How To Test A Capacitor With Multimeter? Different Methods Of Capacitor Test

In Electronic circuits, Capacitor is one of the most commonly used components. During the troubleshooting of such circuits, it is necessary to know how to test a capacitor. 

In this article, we will discuss how to test a capacitor for good, short or opened condition using different methods.

Before testing a capacitor, you need to know about the capacitor itself.

Capacitor

A capacitor is a two-terminal electronic component capable of storing charge in an electric field. It is made up of two metal plates separated by a medium known as the dielectric.

When the capacitor is connected to a battery, an electric field is established between the metal plates. Due to this electric field, the metal plates store charge.

The ability of a capacitor to store charge is known as capacitance. It is measured in farads & denoted by F.

Terminals Of A Capacitor

There are two terminals of a capacitor i.e. positive & negative terminal also known as anode & cathode respectively.

According to its terminal’s polarity, there are two types of capacitors.

Polar Capacitors

Polar capacitors, also known as electrolytic capacitors use electrolyte as one of its terminal to increase the charge storage capacbility. It has high capacitance compared to non polar capacitors.

Its plates are polarized i.e. two unique terminals known as Anode (positive) & Cathode (Negative).

While using a polar capacitor, it is crucial to check for its terminal’s polarity. The anode terminal should always be kept at a higher voltage than its cathode terminals. Reversing the polarity can damage the capacitor and even destroy it.

In simple words, always connect positive with the positive terminal and negative with the negative terminal of a battery.

Non-Polar Capacitor

A non-polar capacitor or non-polarized capacitor has no polarity. There is no difference between its terminals. Both terminals can act as cathode and anode.

Non-polar capacitors have a very low capacitance ranging from few Pico farads to few microfarads.

Also read: Transistor Test for Terminal Identification, Type & Condition.

There are no positive and negative terminals. The terminal connected to the positive terminal of a battery act as Anode. While the terminal connected to the negative terminal of the battery acts as the cathode. Changing the polarity of the battery does not affect the capacitor.

Visual Identification Of Terminals

As we know that non-polar capacitors do not have different terminals. So there is no need for identification of its terminals.

However, it is crucial to identify the terminals of a polar electrolytic capacitor.

First Method

During its manufacturing, the Anode leg of a polar capacitor is made longer as compared to the cathode leg. This method works only when the capacitor is not used. The second method works for both new & used capacitors.

Second Method

The negative terminal of the capacitor is specified on its body with ‘–’ marking pointing to the cathode leg.

However, the polar SMD capacitors have a marking over its positive (Anode) terminal. 

Different Methods Of Capacitor Test

To test a capacitor, you need to remove the capacitor from its circuit, if it is in any circuit. Then discharge the capacitor as it may have some stored charge. It can damage your testing equipment.

To properly discharge a capacitor, connect a resistor between its terminals. The charge will dissipate through the resistor.

A Multimeter is an essential tool required to test a capacitor. Various methods of capacitor test using multimeter are discussed below.

Test A Capacitor Using Continuity Test

The continuity test method for a capacitor shows whether it is opened, short or good.

Also read:Differences Between Capacitor & Battery

Test A Capacitor Using Resistance Test

The resistance test is also used to test a capacitor. Both digital & analog multimeter can perform this test. The method remains the same for both multimeters.

Also read: How To Test A Diode & Methods Of Diode, LED & Zener Diode Test

The reason for increasing resistance is that initially, the capacitor was charging from the multimeter. So it allows the current to flow through(in which case the ohmmeter measures a resistance). When the capacitor got fully charged, it did not allow anymore current. Due to which, it appears as an open path (infinite resistance)

Test A Capacitor Using Capacitance Mode

Capacitance mode is a unique mode in digital multimeters used for measuring the capacitance. If you want to test a capacitor using this method, you need to know how to read a capacitor’s value.

How To Read A Capacitor Value:

Electrolytic capacitor usually specifies the whole value as shown in the figure below.

However, the ceramic capacitor value is written in a code. You can convert/decipher it using its specific method. Example of reading a ceramic capacitor is given below.

The ceramic capacitor shows number 103.

The next step is to its find tolerance. It gives a minimum & maximum range to which the capacitance can vary from its nominal value.

Some of the common tolerance value is specified by the letters j, k, l, m & n as to add/subtract a percentage of 5,10,15,20 & 30 respectively.

Now let’s move forward with the capacitance measurement test.

 

Check A Capacitor By Its Voltage Test:

A capacitor’s ability is to store charge, which reflects as a voltage across its terminals.

This test shows that the capacitor can hold the charge or not. If a capacitor is good, it will store some charge. which will appear as a voltage across its terminal & we can measure it using a voltmeter.

Before testing a capacitor for voltage test, you need to know about the voltage rating of the capacitor.

The voltage rating of the capacitor is always written beside its capacitance value as shown in the figure below.

When charging a capacitor with a battery, the battery voltage should be lower than the nominal voltage of the capacitor. Otherwise, the capacitor will blow.

In this test, we are using a capacitor of 63v rating with a 12-volt battery.

How To Test A Capacitor By Calculating Its RC Time Constant

The RC time constant (denoted by Greek word tau ‘τ’) is the time duration in which a capacitor charges up to 63.2% of its applied voltage.

The time constant τ is calculated by resistance times capacitance:

τ = R C

In this equation, resistor R is of known value & we will measure τ during this test.

In this test, we use a 12v battery with a 10kohm resistor. We connected them in series with the capacitor. We use a voltmeter to measure the voltage across the capacitor and a stopwatch for measuring the time.

Also read: Digital Logic NAND Gate (Universal Gate), Its Symbols, Schematic Designs & IC Details

Suppose the stopwatch reads 9 seconds.

C = τ / R

C = 9/103

C = 0.9mF = 900uF

Visual Checking Of A Capacitor

You can determine a bad capacitor just by observing the signs of it.

A failed or damaged capacitor will show any of the following signs.

Bulging Top Vent:

In the electrolytic capacitors, there is a vent (not actually vent but weak points) in shape of X, K, T on its top. It is made for releasing the pressure during the capacitor failure to avoid any damage(blast) to any other components.

Upon failure, the electrolyte inside the capacitor releases a gas. This gas builds up a pressure and breaks the top vent. The result is sometimes a bulging top or electrolytic discharge. The discharge is of black, orange or white color depending on the electrolytic chemicals. 

Bulging Bottom & Lifted Case

Sometimes during the capacitor failure, the top vent does not break. in such case, the pressure inside finds its way through the bottom. The bottom of an electrolytic capacitor is covered by a rubber. The gas inside pushes this rubber out making the bottom bulging and also lifting its case above its circuit board. 

Ceramic & SMD Capacitors

You can Identify a bad ceramic capacitor by the following signs.

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