How to test a capacitor

How to Test a Capacitor

You’ll find that most of your home appliances have a capacitor. It’s important to know what to do when household equipment starts making noises that it’s not supposed to. If you know how to test a capacitor, then you’ll more than likely be able to find out the root of the problem. Our guide below will help you understand what a capacitor is, what it does, and how to safely test it.

What is a capacitor?

A capacitor is an electrical component that stores the energy between the source and whatever is going to use it. In most cases, you’ll encounter it in your home appliances. Capacitors vary in shapes, sizes, and the amount of electrical energy stored.

How does a capacitor work?

A capacitor essentially works like a battery. The major difference between a capacitor and a battery is that the former can’t produce new electrons.

You will find two metal plates inside a capacitor. They’re separated by a dielectric (non-conducting substance). Making a makeshift capacitor is as easy as putting two pieces of aluminum foil and a sheet of paper.

Besides energy storage, capacitors can also be used for power conditioning. Capacitors let AC signals pass constantly, but stop DC signals as soon as they’re charged.

Another use of capacitors are as sensors. Air humidity can be measured using a capacitor. In your motor vehicle, you’ll find a capacitor that indicates fuel levels and even the strain on your car’s components.

Lastly, capacitors can be used to process signals. DRAMs, which stands for Dynamic Random Access Memory, are devices that use capacitors to replace and represent stored binary information. You’ll find that this is common with speakers, radios receivers, and other equipment that uses frequencies to process information.

What are capacitors made of?

There are a variety of materials used for capacitor production. These include:

  • Teflon
  • Mylar
  • Mica
  • Ceramic
  • Cellulose
  • Porcelain
  • Air

Air, the last one on the list above, is used primarily for the circuits of radio tuning. The most common one, however, is Mylar. Mylar is used for timer circuits such as clocks, alarms, and time counters. Pick up the nearest clock or watch from you and you’ll see a capacitor made of Mylar inside.

How to check a capacitor’s status

There are a number of methods that you can follow to test a capacitor. We strongly discourage you from doing any of them unless you’re supervised or are a professional.

Method 1

This method is what many professionals call the “traditional” method. It’s what many electrical engineers use to test the capacitor for fans and air coolers.

Warning: Do not use 230V AC. Use 24V DC for a safer experience. If you don’t have a DC 24V system, then you can use a 220-224V AC with resistors that connect the capacitor to the 230V AC supply. This enhances safety by reducing the amount of current that is charged and discharged.

  • Disconnect the capacitor from the power supply. Make sure that this specific capacitor is fully discharged
  • Connect all of the leads to the terminal of the capacitors
  • Connect these leads to the 230 V AC supply for up to 4 seconds, or until the voltage rises to at least 63.2%
  • Remove the safety leads from your 230 V AC supply then quickly short the capacitor terminal. Be careful during this step since a lot can go wrong in a short amount of time.

If the capacitor makes a weak spark, then you have to replace it as soon as possible. On the other hand, a strong spark indicates that your capacitor is still in good condition.

Method 2

This method takes advantage of a digital multimeter. A DMM is a tool used to test two or more electrical values such as voltage, current, and resistance.

  • Discharge the capacitor
  • Adjust the Ohm range meter to at least 1000 Ohm
  • Connect the meter leads to the terminals of your capacitor
  • Take note of the numbers displayed on the DMM. You have to be quick during this step since what’s displayed on the meter will return to the OL
  • Repeat the steps at least 3 times

If every number displayed during steps 2 and 4 are the same, then the capacitor needs to be replaced. Otherwise, you have a good capacitor with you.

Method 3

This method uses an analog multimeter to check and test your capacitor.

  • Fully discharge your capacitor.
  • Take the analog meter and select the higher range for Ohms
  • Connect the leads of the meter to the terminals of the capacitor
  • Take note of the reading on the AVO meter and compare the results

Low resistance means that you have a shorted capacitor. No movement on the OHM meter display means that you have an open capacitor. A good capacitor is indicated by the gradual increase of the number displayed up to infinite.

Method 4

This method is mostly used for small capacitors. You can take advantage of the capacitance meter on your multimeter tool for this method.

  • Fully discharge your capacitor
  • Remove the capacitors from the circuit or the board
  • Select the capacitance mode on your multimeter tool
  • Connect the leads of the multimeter to the capacitor terminal

A good capacitor will show a reading that’s close to the printed number on the capacitor container box. If it’s significantly lower, then you need to replace the capacitor as it is dead.


Learning how to test capacitor levels is the best way to know if your capacitor is still in working condition. It’s important that you immediately replace a faulty, shorted or dead capacitor to prevent worse damage to your home appliances. What you’ve read above are only some of the safest methods for beginners. Consulting the help of a professional is always what we suggest to those who suspect that they have a broken capacitor.

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