How To Test a Capacitor with a Multimeter

A common issue I get people asking me is how they can test a capacitor with a multimeter.

The capacitor’s nature is to charge and release energy faster than a battery because it stores energy differently, although it can’t store as much. This is very useful and is why you can find a capacitor in almost every circuit board.

The capacitor stores energy released to smooth out current interruptions to the supply.

Inside a basic capacitor, we have two conductive plates, typically made from aluminum, separated by dielectric insulating materials such as ceramic.

Dielectric means the material will polarize when in contact with an electric field. On the side of the capacitor, you will find a symbol and a stripe indicating which side(lead) is negative.

Ways to Test a Capacitor Using a Multimeter

At first, you have to make sure that you know what you’re doing. Carefully read out the warnings before applying these methods of testing a capacitor.

You also have to determine the main failure modes, which means what is the suspected fault in the capacitor, so you can know what testing method to use:

• Decrease in capacitance
• Dielectric breakdown (short-circuit fault)
• Loss of contact between plate and lead
• Leakage current
• Increased ESR (equivalent serial resistance)

Check a capacitor with a digital multimeter

1. Disconnect the capacitor from the power supply, or at least make sure one lead is disconnected.
2. Make sure the capacitor is fully discharged. This can be achieved by bridging both leads of the capacitor with a screwdriver.
3. Set the meter on the Ohm range (at least 1kOhm)
4. Connect the multimeter leads to the capacitor terminals. Make sure you connect positive to positive and negative to negative.
5. The meter will show some numbers for a second, and then immediately, it will return to OL(Open Line). Every attempt at Step 3 will show the same result as in this step.
6. If there is no change, it means that the capacitor is dead.

Check a Capacitor in Capacitance Mode.

For this method, you will need to have a capacitance meter on your multimeter or have a multimeter that includes this feature.

This method is best for testing smaller capacitors. For this test, switch to capacitance mode.

1. Disconnect the capacitor from the power supply, or at least make sure one lead is disconnected
2. Make sure the capacitor is fully discharged. This can be achieved by bridging both leads of the capacitor with a screwdriver.
3. Select “Capacitance” on your device.
4. Connect the multimeter leads to the capacitor terminals.
5. If the reading is near the value printed on the capacitor container box, that means the capacitor is in good condition. The reading might be less than the actual value of the capacitor, but that is normal.
6. If you read no capacitance or significantly smaller capacitance than the reading suggests, it means the capacitor is dead and should be changed.

Check the Capacitor with A Voltage Test.

This is yet another way you can test your capacitor. Capacitors store a potential difference in charges, which are voltages.

The capacitor has an anode (positive voltage) and a cathode (negative voltage).

One way to test your capacitor is to charge it up with voltage, then read it across the cathode and anode. For this, it is necessary to apply DC voltage to the leads. Here, polarity is important. If the capacitor has both positive and negative leads, it is a polarized capacitor, in which positive voltage will go to the anode and negative to the cathode.

1. Disconnect the capacitor from the power supply, or at least make sure one lead is disconnected
2. Make sure the capacitor is fully discharged. This can be achieved by bridging both leads of the capacitor with a screwdriver, although, for bigger capacitors, it would be better to discharge through a load.
3. Check the voltage range rating that is printed on the capacitor
4. Apply a voltage, but be careful and be sure that there is less voltage than the capacitor is rated for; for example, you can use a 9V battery to charge a 16V capacitor and make sure to connect the positive leads to the positive leads of the capacitor as well as the negative to the negative leads.
5. Charge the capacitor for a few seconds
6. Remove the voltage source (the battery)
7. Set the value of the meter to DC and connect the voltmeter to the capacitor by connecting the leads positive-positive and negative-negative
8. Check the initial read of the voltage. It should be close to the supplied voltage given to the capacitor. This means the capacitor is in good condition. If the reading is too small, the capacitor is dead.

The voltmeter will show this reading for a very short time because the capacitor will start rapidly discharging through the voltmeter to 0V.