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Home » Capacitors » How to Test a Capacitor? 6 Ways to Check a Capacitor.

How to Test a Capacitor? 6 Ways to Check a Capacitor.

How to Test & Check a Capacitor with Digital Multimeter and Analog AVO Meter.

By six (6) Methods with pictorial Views.

In most electrical and electronics troubleshooting and repairing works, we face a common trouble that 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 multi meter either it is in good condition or should we replace it with a new one..

Note: To find the Value of Capacitance, you need a digital meter with Capacitance measuring features.How to Test a Capacitor with Digital Multimeter and Analog AVO Meter. By six (6) Methods with pictorial View.

Below are five (6) methods to check & test that a Capacitor is Good, Bad, Open, Dead, or Short.

Also Read:

Method 1.

Traditional Method to test & check a capacitor (Not Recommended for everyone but professionals only)

Note: This method is dangerous, please be careful to do this practice. Make sure that you are a professional electrical engineer / electrician (you really know that what are you doing or check the warnings before applying this method) and there are no other options to check the capacitor because serious damages may occur during this practice). If you are sure, go ahead, otherwise, go to method 2 – 6 as alternative methods to a capacitor.

Suppose you want to check the Capacitor (for example, fan capacitors, room air cooler capacitors or tinny capacitors in a circuit board / PCB etc.)

Warning & recommendations for testing a capacitor by method 1.

For better safety, use 24V DC instead of 230V AC. In case of absence of the desired DC 24V system, you may use 220-224V AC, but you have to make a serial of resistors (say 1kΩ~10kΩ, 5~50Watts) to connect between capacitor and 230V AC supply.So that, it will reduce the charging and discharging current. Here is the step by step tutorial that how may you check a capacitor by this method.

  1. Disconnect the suspected capacitor from the power supply or make sure at least one lead of the capacitor is disconnected.
  2. Make sure that the capacitor is fully discharged.
  3. Connect two separate leads to the capacitor terminals. (Optional)
  4. Now safely connect these leads to 230 V AC Supply for a very short period (about 1-4 Sec) [or for a short time where the Voltage rise to 63.2% of the Source Voltage] .
  5. Remove safety leads from the 230 V AC Supply.
  6. Now short the capacitor terminals (Please be careful to do that and make sure that you have wear safety goggles)
  7. If it makes a strong spark, then the capacitor is good.
  8. If it makes a weak spark, then it is a bad capacitor and change it immediately with a new one.

How to Check a Capacitor with Digital Multimeter and Analog AVO Meter. five Methods (pictorial) View

Method 2.

Check & Test a Capacitor By Analog Multimeter ( AVO = Ampere, voltage, Ohm Meter )

  1. Make sure the suspected capacitor is fully discharged.
  2. Take an AVO meter.
  3. Select analog meter on OHM (Always, select the higher range of Ohms).
  4. Connect the Meter leads to the Capacitor terminals.
  5. Note The reading and Compare with the following results.
  6. Short Capacitors: Shorted Capacitor will show very low Resistance.
  7. Open Capacitors: An Open Capacitor will not show any movement (Deflection) on OHM meter Screen.
  8. Good Capacitors: Initially, it will show low resistance, and then gradually increases toward the infinite. It means that Capacitor is in Good Condition.

how to check that is a capacitor is good, open, dead, or short?

Method 3.

Test & Check a Capacitor By a Digital Multimeter

  1. Make sure the capacitor is discharged.
  2. Set the meter on Ohm range (Set it at lease 1000Ohm = 1k).
  3. Connect the meter leads to the capacitor terminals.
  4. Digital meter will show some numbers for a second. Note the reading.
  5. And then immediately it will return to the OL (Open Line). Every attempt of Step 2 will show the same result as was in step 4 and Step 5. It’s mean that Capacitor is in Good Condition.
  6. If there is no Change, then Capacitor is dead.

How to Check a Capacitor with Digital Multimeter and Analog AVO Meter. 5 Methods
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Method 4.

Checking Capacitor By Multimeter in the capacitance Mode

Note: You can do this test with a multimeter if you have a Capacitance meter on your multimeter. Also, this method is good for tiny capacitors.

  1. Make sure the capacitor is fully discharged.
  2. Remove the capacitors from board or circuit.
  3. Now Select “Capacitance” on your multimeter.
  4. Now connect the capacitor terminal to the multimeter leads.
  5. If the reading is near to the actual value of the capacitor (i.e. the printed value on the Capacitor container box).
  6. Then the capacitor is in good condition. (Note that the reading may be less than the actual value of the capacitor (the printed value on the Capacitor container box).
  7. If you read a significantly lower capacitance or none at all, then capacitor is dead and you should change it.

how to check a capaccitor that is good, bad, open, dead or short?
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Method 5.

Check and test a capacitor by simple voltmeter.

  1. 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 when needed)
  2. Check the capacitor voltage rating printed on it (As shown in our below example where is the voltage = 16V)
  3. Now charge this capacitor for a few second to the rated (not to the exact value but less than that i.e. charge a 16V capacitor with 9V battery) 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 unable to find it or not sure, here is the tutorial how to find the negative and positive terminal of a capacitor.
  4. Set the value of voltmeter to the DC and connect the Capacitor to the voltmeter by connecting the positive wire of battery to the positive lead of capacitor and negative to negative.
  5. Note the initial voltage reading in the voltmeter. If it is close to the supplied voltage you given to the capacitor, the Capacitor in in Good condition. If it shows far little reading, Capacitor is dead then. note that the voltmeter will show the reading for very short term as the capacitor will discharge its volt in the voltmeter and it is normal.

Check & Test a Capacitor by Simple Voltmeter.

Find the capacitor value 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 burnt 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 (TC or τ = Tau) and can be calculated via:

τ = RxC

Where:

R = Known Resistor

C = Value of Capacitance

τ = TC or τ = Tau (Time Constant)

For instance, if the supply voltage is 9V, then 63.2% of this is around 5.7V.

Now, let see how to find the value of a capacitor by measuring the Time Constant.

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 10kΩ resistor.

Now, measure the time taken for the capacitor to charge about the 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 given resistor and measured time, calculate the value of capacitance by Time Content formula i.e. τ = TC or τ = Tau (Time Constant).

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

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

The discharge time can also be calculated. In this case, the time take by the capacitor to discharge to 36.8% of the peak voltage can be measured.

Good to know: The time taken by a capacitor to discharge about 36.8% of the peak value of the applied voltage can be also measured. The discharge time can be used as same in the formula to find the value of capacitor.find the value of a capacitor by measuring the Time constant

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43 comments

  1. EXCELLENT TUTORIAL

  2. Thank you. This is very useful information.

  3. just found this article that gives a far safer and good way to perform basic test on a capacitor forum.allaboutcircuits.com/showthread.php?t=5326<br the current article is very lacking in warnings and contains dangerous advice, I am an electronics engineer and as I said in my previous comment a professional would NEVER place a suspect cap across the mains like that

  4. A professional would NEVER try option 1, if this was April 1st I could see this being published, <br />Capacitors DONOT store AC volts, to wack mains across an arbitrary capacitor is going to get someone KILLED, this option should be removed ASAP<br /><br />the whole theory is wrong…<br /><br />a capacitor rated at 250V AC does not mean it will store AC and capacitors are not rated for power

  5. I agree that method 1 is very dangerous.

  6. nice it is very use ful parameters

  7. nice it is very use ful parameters
    and i see it done by electician to check the capacitor

  8. Wow that was good to know! This tutorial show how to use a digital multimeter (DMM), an indispensable tool that can use to diagnose circuits. The most basic things we measure are voltage and current. A multimeter is also great for some basic sanity checks and troubleshooting. Now this tester is also available which makes electrical testing easier with a wide range of multifunction testing accessories and ancillaries.Thanks

  9. Thanks. Sir
    It’s the science of alms

  10. I agree. Connecting a suspect capacitor across mains is very dangerous. Capacitors used in
    AC circuits are generally for delaying the AC cycles to mimic another phase. This second phase helps in turning AC motors. It also supplies a current boost to get the motor turning.

  11. very good educational,thank a lot

  12. Thank you on the capacitor info.

  13. I truly find the information about the capacitor very useful. Thanks

  14. how can use DMM to measure variable capacitor. thanks

  15. Thank you very much for this perfect training

  16. how to measure capictance for 1 hp motor or 70 watt fan, any formula? please help..

  17. None of these methods will determine if a capacitor is good, although some of them will show you if a capacitor is bad. A capacitor has to be tested at it’s rated voltage and the current draw must meet the specs at the rated voltage.

  18. Good tutorial.

  19. Although most of this info is helpful, one of the issues I have found is the assumption that the capacitor isn’t breaking down under load. None of these tests would show this.

    There is also another option to testing a capacitor (or inductor), if you have an o’scope available. It’s called an Octopus, and can be built using scrap parts. This site has a schematic: http://levysounddesign.blogspot.com/

    Lastly, in my 40 years as an Electronics Tech, I’ve never heard of an Analog Multimeter referred to as an AVO Meter. Interesting.

  20. In checking the value of a capacitor of nF range with a digital multimeter , should the board be powered up or not ???

  21. Hello, every time i used to check website posts here early in the daylight, as i like to find out
    more and more.

  22. hello sir
    can I check ht capacitor from this method and also charge from ht megger for checking.

  23. ht capacitor fuse blown possible reasons

  24. I heard along time ago that if you put the positive to the positive lead of the capacitor and the negative to the negative, it will show a charge. Flip the leads and it will show a discharge. Any truth to this?

  25. Olanrewaju Akinwale.A

    Brilliant training ?????????
    How do I learn more from you sir and your duration of study for student. Minimum months and maximum years sir.
    Kindly reply to my email sir

  26. Thanks a lot for this information.

  27. Item 1 regarding shorting the capacitor is extremely dangerous and should be deleted from this article. There is a severe danger of arc, severe damage of contacts, possible electrocution, etc.

    There is another test using an ESR digital meter that usually uses high frequency and low voltages that will give a better representation if the capacitor is failing or not. Look into adding the ESR meter as a preferred method.

  28. Can i charge a caoacitor with 220v ac

  29. Very good information thanks

  30. A good article, detailed introduction, easy to understand

  31. “Method 1.
    Traditional Method to test & check a capacitor (Not Recommended for everyone but professionals only)”

    um… so why would a p[professional even be reading this?

  32. In practically (method I) we shall check the capacitor by series circuit with 200 watt bulb charge the capacitor than short it.

  33. Engr.Imran Mollick

    Thank a lot.

  34. if time constant is very low using the resistance 10k
    how to find capacitance value for low value of capacitance ?

  35. Thank you for this valuable and very useful information.
    Please provide the information about High voltage polyster film capacitor testing

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