How to test a capacitor with a multimeter

Often people ask me how to test a capacitor with a multimeter.

The nature of a capacitor is to charge and release energy faster than a battery because it stores energy differently, although it cannot store the same amount. This is very useful and that is why you can find a capacitor on almost every PCB.

The capacitor stores the energy released to smooth out power outages.

Inside the main capacitor, we have two conductive plates, usually made of aluminum, separated by dielectric insulating materials such as ceramic.

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

Ways to test a capacitor with a multimeter

First you have to make sure you know what you are doing. Read the warnings carefully before using these capacitor test methods.

You should also determine the main failure modes, which means the suspected failure of the capacitor, so you can know which testing method to use:

• Capacity reduction
• Dielectric breakdown (short circuit)
• Loss of contact between plate and lead
• leakage current
• Increased ESR (equivalent series resistance)

Check the capacitor with a digital multimeter

1. Disconnect the capacitor from the power supply, or at least make sure one wire is disconnected.
2. Make sure the capacitor is fully discharged. This can be achieved by connecting both terminals of the capacitor with a screwdriver.
3. Set the meter to the ohm range (at least 1k ohm)
4. Connect the multimeter leads to the capacitor terminals. Make sure you connect positive to positive and negative to negative.
5. The counter will show a few digits for a second and then immediately return to OL (open line). Each attempt in step 3 will show the same result as in this step.
6. If there is no change, then the capacitor is dead.

Check the capacitor in capacitance mode.

For this method, you will need a capacitance meter on a multimeter, or a multimeter with this feature.

This method is best for testing small capacitors. For this test, switch to capacity mode.

1. Disconnect the capacitor from the power supply, or at least make sure one wire is disconnected.
2. Make sure the capacitor is fully discharged. This can be achieved by connecting both terminals of the capacitor with a screwdriver.
3. Select "Capacity" on your device.
4. Connect the multimeter leads to the capacitor terminals.
5. If the reading is close to the value indicated on the box of the capacitor container, it means that the capacitor is in good condition. The reading may be less than the actual value of the capacitor, but this is normal.
6. If you don't read the capacitance, or if the capacitance is significantly less than the reading suggests, the capacitor is dead and should be replaced.

Check Capacitor with voltage test.

This is another way to test a capacitor. Capacitors store potential differences in charges, which are voltages.

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

One way to test a capacitor is to charge it with voltage and then take readings at the cathode and anode. To do this, apply a constant voltage to the outputs. Polarity matters here. If a capacitor has both positive and negative terminals, it is a polarized capacitor in which the positive voltage will go to the anode and the negative voltage to the cathode.

1. Disconnect the capacitor from the power supply, or at least make sure one wire is disconnected.
2. Make sure the capacitor is fully discharged. This can be achieved by shunting both terminals of the capacitor with a screwdriver, although larger capacitors are best discharged through the load.
3. Check the voltage range marked on the capacitor.
4. Apply voltage, but be careful to make sure the voltage is less than what the capacitor is rated for; for example, you can use a 9 volt battery to charge a 16 volt capacitor and be sure to connect the positive leads to the positive leads of the capacitor and the negative leads to the negative leads.
5. Charge the capacitor in a few seconds
6. Remove voltage source (battery)
7. Set the meter to DC and connect a voltmeter to the capacitor, connecting positive-to-positive and negative-to-negative.
8. Check the initial voltage value. It should be close to the voltage applied to the capacitor. This means that the capacitor is in good condition. If the reading is too low, the capacitor is discharged.

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