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8 Ways to Check and Test a Capacitor with a DMM and AMM (AVO)

In most electrical and electronics troubleshooting and repairing works, we face a common problem with capacitors where we want to know how to test and check a capacitor? Is it good, bad (dead), short or open?

Here, we can check a capacitor with analog (AVO meter i.e. Ampere, Voltage, Ohm meter) as well as digital multimeter Either the capacitor is in good condition or we should replace it with a brand new one.

Note: To find the value of Capacitance, you need an analog or digital multimeter with capacitance measuring features.

Below are eight (8) methods to check & test that a Capacitor is Good, Defective, Open, Dead, or Short.

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Method 1.

Test a Capacitor using Digital Multimeter – Resistance Mode

To test a capacitor by DMM (Digital Multimeter) in the Resistance “Ω” or Ohm mode, follow the steps given below.

Make sure the capacitor is fully discharged.

Set the meter on the Ohmic range (Set it at least on 1000 Ohm = 1kΩ).

Connect the multimeter probes to the capacitor terminals (Negative to Negative and Positive to Positive).

Digital multimeter will show some numbers for a second. Note the reading.

And then immediately it will return to the OL (Open Line) or infinity “∞”. Every attempt of Step 2 will show the same result as shown in steps 4 and 5. It means that Capacitor is in Good Condition.

If there is no change, then Capacitor is dead.

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Method 2.

To check a capacitor by AVO (Ampere, Volt, Ohm Meter) in the Resistance “Ω” or Ohm mode, follow the following steps.

Make sure the suspected capacitor is fully discharged.

Take an AVO meter.

Rotate the knob on the analog meter to select the resistance “OHM” mode (Always, select the higher range of Ohms).

Connect the Meter leads to the capacitor terminals. (COM to the “-Ve” and Positive to the “+Ve” terminals).

Note the reading and compare with the following results.

Short Capacitors: Shorted Capacitor will show very low resistance.

Open Capacitors: An Open Capacitor will not show any movement (Deflection) on the OHM meter scale.

Good Capacitors: Initially, it will show low resistance, and then gradually increases toward the infinite. It means that the capacitor is in good condition.

Checking Capacitor using Multimeter in the Capacitance Mode

Note: Testing a capacitor in the capacitance mode can only be performed if the analog or digital multimeter has the farad “Farad” of Capacitance “C” features. The function of capacitance mode in a multimeter can also be used to test the tiny capacitors. To do this, rotate the knob of the multimeter to the capacitance mode and follow the following basic instructions.

Make sure the capacitor is fully discharged.

Remove the capacitors from the circuit board.

Now Select Capacitance “C” on the multimeter.

Now connect the capacitor terminal to the multimeter leads. (Red to Positive and Black to Negative).

If the reading is close to the actual value of the capacitor (i.e. the value printed on the Capacitor container box).

Then the capacitor is in good condition. (Note that the reading may be less than the actual value of the capacitor (the rated value of capacitor due to the tolerance in ±10 or ±20).

If you read a significantly lower capacitance or none at all, then the capacitor is dead and you should change it with a new one for proper operation.

Testing a Capacitor By Simple Voltmeter

To apply this method on polar and nonpolar capacitors, you must know the value of nominal voltage of capacitors. The level of voltage is already printed on the nameplate of electrolytic capacitors. While there are specific codes printed on ceramic and SMD capacitors. You may follow this guide which shows how to read and find the value of ceramic and non-polarized capacitors with related codes printed on it.

Also, you can use the DC Voltage “V” or Volt Mode in the digital or analog multimeter to perform this test.

Make sure to disconnect a single lead (no worries if Positive (long) or negative (short)) of the capacitor from circuit (You may fully disconnect as well if needed)

Check the capacitor voltage rating printed on it (As shown in our below example where the voltage = 16V)

Now charge this capacitor for a few seconds to the rating (not to the exact value but less than that i.e. charge a 16V capacitor with 9V battery. If the value of battery voltage is greater than the nominal voltage of the capacitor, it will damage or burst the capacitor.) voltage. Make sure to connect the positive (red) lead of the voltage source to the positive lead (long) of the capacitor and negative to negative. If you are not sure or unable to find the proper leads, here is the tutorial on how to find the negative and positive terminal of a capacitor.

Set the value of the voltmeter to the DC voltage and connect the capacitor to the voltmeter by connecting the positive wire of the battery to the positive lead of the capacitor and negative to negative. You can use a digital or analog multimeter while selecting the DC voltage range for the same purpose.

Note the initial voltage reading in the voltmeter. If it is close to the supplied voltage you gave to the capacitor, the Capacitor in is in Good condition. If it shows far less reading, Capacitor is dead then. Note that the voltmeter will show the reading for a very short time as the capacitor will discharge its stored volts in the voltmeter.

Test the Capacitor by Measuring the Value of Time Constant

We can find the value of a capacitor by measuring the Time Constant (TC or τ = Tau) if the value of capacitance of a capacitor is known in microfarad (symbolized µF) printed on it i.e. The capacitor is not blown and burned at all.

In brief, the time taken by a capacitor to charge about 63.2% of the applied voltage when charges through a known value of resistor is called Time Constant of Capacitor (τ = Tau also known as RC time constant) and can be calculated via:

τ = R x C

R = Value of known resistor in Ohms

C = Value of Capacitance

τ = Tau (Time Constant)

For instance, if the supply voltage is 9V, then 63.2% of the supply voltage is around 5.7V. We will use a stopwatch and charge the capacitor until the value reaches 5.7V. Stop the watch and note the reading of time in seconds. For more details, check the example given below the instructions.

Now, let’s see how to find the value of a capacitor by measuring the Time Constant. (Note: An oscilloscope will do this better with precise value instead of multimeter.

Make sure to disconnect as well as discharge the capacitor from the board.

Connect a known value of resistance (e.g. 5-10kΩ Resistor) in series with the capacitor.

Apply the known value of supply voltage. (e.g. 12V or 9V) to the capacitor connected in series with a 10kΩ resistor.

Now, measure the time taken for the capacitor to charge about 63.2% of the applied voltage. For instance, if the supply voltage is 9V, then 63.2% of this is around 5.7V.

From the value of the given resistor and measured time via a stopwatch, calculate the value of capacitance by Time Constant formula i.e. τ = Tau (Time Constant).

Now compare the calculated value of capacitance with the value of capacitor printed to it.

If they are the same or nearly equal with , the capacitor is in good condition. If you find a noticeable difference in both values, time to change the capacitor as it is not working well.

Example: Suppose, we are going to test a 16V, 470μF capacitor. If the supply voltage is 9V, then 5.7V is 63.2% of the supply voltage. We will connect the capacitor to the battery for charging and start the stopwatch. When the meter shows a 5.7V, we will stop the stopwatch. Suppose, the stopwatch shows 4.7 seconds of time duration.