How To Test A Capacitor? A Complete Guide!

Testing a capacitor might seem a challenging task. However, it is not as difficult as it seems, and this guide will help you learn about it. Before proceeding, it is important to start by understanding that capacitors are precise elements used in electrical circuits, the main purpose of which is to accumulate energy and release it at an agreed time according to the plan put in place. It can be of different forms and designs and manufactured using different types of materials; nevertheless, they all consist of two terminals joined to a circuit. 

What is a Capacitor?

A capacitor is made up of two plates that are connected but are separated by a dielectric or an insulating material. The plates can be of metal, foil, or other conductive material, while the dielectric may be air, paper, ceramic, or plastic. When one terminal of a voltage is connected to one plate and the other terminal to the other plate of the capacitor, positive and negative charges build up at the plates, respectively, leading to the formation of an electric field. The quantity of charge that can be stored depends on the voltage, the size of the plates, the shape of the plate, the type of the dielectric, and the thickness of the dielectric. 

Applications of Capacitors

Capacitors are versatile components used in numerous applications:

• Voltage Smoothing 
• Signal Filtering
• Energy Storage
• Coupling Circuits
• Tuning Radios
• Data Storage

How to Test a Capacitor with a Multimeter?

Here's your answer to the question- how do I test a capacitor with a multimeter:  

1. Disconnect the Capacitor: Make sure that the capacitor is not connected to any power source or any other component.
2. Discharge the Capacitor: When connected to a circuit, capacitors can hold a charge even when disconnected, which can be dangerous while testing. To safely remove the capacitor, briefly touch the terminals with the resistor or the end of a screwdriver. 
3. Read the Capacitance Value: The capacitance value is usually marked on the body of the capacitor or in the form of a code on the capacitor case on the body of the capacitor. It indicates capacitance value in farads F, microfarads µ F nanofarads nF, or picofarads pF. They may consist of other marks intended for tolerance, voltage, coefficient of temperature, or even the manufacturer's code number. 
4. Set the Multimeter: Put the switch of the multimeter to a position marked as ‘C’ or with the symbol of two parallel lines with a bump in between them, and this is for capacitance. 
5. Connect the Leads: Clip the red multimeter probe to the capacitor’s + (red) terminal and the black multimeter probe to the – (larger) terminal. 
6. Check the Reading: The capacitance value will be indicated by the multimeter. Compare the numeric value you obtained to the value stated on the printed text on the capacitor. Therefore, if the measured value is close to the printed value and lies within the tolerance limit, the capacitor is in good condition. A considerably lower value than the value on the label or zero means that the capacitor is bad. 

Read More - Choosing the Right Capacitor Bank for Power Factor Correction!

How To Test a Capacitor with Resistance?

If you wish to know how you test an AC capacitor or any other with resistance, below are the steps to follow. 

1. Disconnect the Capacitor: Make sure that the capacitor is not connected to a power supply or any other circuitry in any way. 
2. Discharge the Capacitor: To discharge the capacitor, use a resistor, screwdriver, alligator clip, or jumper wire and touch the two terminals of the capacitor to short them out. 
3. Set Multimeter to Resistance: Switch ON the multimeter and set it to the resistance mode as indicated by the symbol ‘OHM’ or Ω. Please select a range of 1K ohm or higher, and when inserting the compensators, the probes must be in the upper segments. 
4. Connect Leads: The red (positive) multimeter lead should be connected to the positive terminal, while the black (negative) multimeter leads to the negative terminal of the capacitor. An essential aspect of capacitors that are polarized is polarity. 
5. Check the Reading: The multimeter‘s reading should show very low resistance, constantly rising towards the letters OL. This also shows that the capacitor is charging and discharging correctly. Thus, it shows that the capacitor is good. Mostly, a reading that constantly reads low or a reading of 0 signifies a bad capacitor. 

How To Test a Capacitor with a Voltmeter?

Follow the below given steps if you wish to know how you test a start capacitor or any other with a voltmeter. 

1. Disconnect the Capacitor: Make sure that the capacitor is not connected to any power source or any circuit component. 
2. Discharge the Capacitor: Discharge the capacitor with a resistor, screwdriver, alligator clip, or jumper wire, making sure you do not get shocked. 
3. Check Voltage Rating: Check the given voltage rating on the body of the capacitor by using a multimeter; it is also mentioned on the body. It is strictly advised not to go beyond this voltage, specifically while testing.
4. Charge the capacitor: After determining a voltage of 10 percent less than the rated voltage, apply the known voltage. For instance, one should use a 9V battery for a capacitor with a rating of 10V. Screw the positive terminal of the power source to the positive terminal of the capacitor and the negative terminal of the power source to the negative terminal of the capacitor. 
5. Set Voltmeter to DC Voltage: Now turn the knob of the voltmeter to point this meter to measure DC voltage. 
6. Connect Leads: Connect one end of the red (positive) voltmeter to the positive terminal of the capacitor while the other end of the black (negative) voltmeter leads to the negative terminal of the capacitor. 
7. Note Initial Voltage: Read the voltage values of the battery top-off. The readings should be very close to the charging voltage if the capacitor is healthy. 
8. Disconnect and Wait: The voltmeter should be disconnected now and wait for some time. 
9. Reconnect and Check Final Voltage: Connect the voltmeter leads again and see the voltage. When the potential difference across the capacitor is measured again, it should be nearly the initial value of a good capacitor that can hold a charge. The relative decrease of such an indicator proves the presence of a bad capacitor. 

Read More -  Capacitor Bank Testing: Importance and Procedures Explained

Summing Up

Capacitors are used in many electrical and electronic circuits to carry out voltage regulation, data filtering, energy storage, and many other functions. It is significant to know how you test a motor capacitor or any other using resistance or voltage techniques so that the performance of electronic units will not be compromised. These tests will reveal broken capacitors before they cause severe problems, extend the lives of the circuits, and assist in making sure that they are performing to the best of their ability. Regardless of whether you are using a multimeter or a voltmeter, you have to discharge, disconnect, and then take a measurement to determine the condition of the capacitor. By applying these testing procedures, you can achieve control and resolution for capacitors’ management, consequently improving the performance of the electronics systems.

Frequently Asked Questions

Q1. How do you test a motor capacitor?

Ans: To test a motor capacitor, first disconnect and discharge it safely. Use a multimeter set to go into capacitance mode and connect the leads to the capacitor terminals. A good capacitor will show a capacitance value close to its rating. Alternatively, an ohmmeter reading should start low and rise to infinity.

Q2. What is a leaky capacitor?

Ans: A leaky capacitor has reduced insulation resistance, allowing current to flow through the dielectric. This can be tested by checking the capacitor’s equivalent series resistance (ESR) with an ESR meter.

Q3. Can you test a capacitor in-circuit?

Ans: It is possible but not always accurate due to other components affecting the measurement. For best results, test the capacitor out of the circuit.