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To check if a Capacitor is functioning at a right value, Capacitor Testing becomes necessary. This post will discuss about what do you understand by Capacitor Testing, methods to test the capacitor step by step in various ways and it’s advantages.

What is Capacitor

Capacitor is a device used to store energy electrostatically in an Electric Field. It is a passive two-terminal electrical component. The Capacitor is made of two close conductors or plates that are separated by a dielectric material. The plates store electric charge when connected to a power source.

Introduction to testing Capacitor

Fig. 1 – Introduction to Capacitor Testing

Read More about Capacitors:
Capacitor Theory
How Capacitor Works
Capacitor charging and discharging cycle
Capacitor Number Marking – How to Decode with Example
How to Read Capacitor Color Marking Values – Calculation and Identification Codes
Different Type of Capacitors in Market with Description – Part I
Different Capacitor Types in Market with Description – Part II
Electrolytic Capacitor – Properties, Uses, Capacitance Value and Polarity
Ceramic Capacitor – Composition, Types, Properties and Applications
What is Supercapacitor (Ultracapacitor) – Characteristics, Working, Types & Applications

 

How to Test a Capacitor – Step by Step Methods

Like all electrical devices, a Capacitor is also sensitive to spikes. Such voltage swings can damage the Capacitors. Therefore, it is necessary to test the Capacitors regularly by following any of the methods given below. Different types of Capacitors are shown in Fig. 2.

Types of Capacitors

Fig. 2 Different Types of Capacitors

  • Capacitor Testing using Multimeter with Capacitance Setting
  • Capacitor Testing using Multimeter without Capacitance Setting
  • Capacitor Testing by measuring the Time Constant
  • Capacitor Testing with simple Voltmeter
  • Capacitor Testing using Analog Multimeter
  • Capacitor Testing by Shorting the Leads

Capacitor Testing using Multimeter with Capacitance Setting

  1. The Capacitor must be disconnected from the circuit board and then it should be discharged completely.
  2. A note should be made if the ratings of the capacitor are visible on its body.
  3. The knob of the Digital Multimeter must be set to capacitance settings.
  4. Next, the Multimeter probes must be connected to the terminals of the Capacitor.
  5. After that, the readings on the Digital Multimeter must be checked. If the Multimeter readings are nearer to the actual values (referenced on the capacitor), at that point the Capacitor can be considered as operational. On the contrary, if the difference between the actual value and the measured reading is significantly large (or sometimes zero), then the capacitor should be replaced as it is a dead one.

Multimeter

Fig. 3 – Image of Digital Multimeter

Capacitor Testing using Multimeter without Capacitance Setting

  1. At first, the Capacitor must be disconnected from the circuit board and then it should be discharged completely.
  2. Then, the knob of the Multimeter must be set to Ohm or Resistance Settings. In case of multiple ranges of resistance measurement, a higher range (usually 20 KΩ to 200 KΩ) should be selected.
  3. Next, the Multimeter probes must be connected to the terminals of the Capacitor. In case of an Electrolytic Capacitor, the red probe must be connected to the positive terminal of the capacitor and the black probe must be connected to the negative terminal of the Capacitor. In case of Non-Electrolytic Capacitor, it can be connected in either way.
  4. After that, a reading of resistance will be shown on the display by the Digital Multimeter. It will then display the resistance of an open circuit (i.e. infinity). The reading for that short period should be noted down.
  5. Then, the Capacitor must be disconnected from the Multimeter and the test must be repeated several times.
  6. For a good Capacitor, every attempt of the test should show a similar result on the display. If in the further tests there is no change in the resistance, then the capacitor should be replaced as it is a dead one.

Capacitor Testing by Measuring the Time Constant

  1. At first, the Capacitor must be disconnected from the circuit board and then it should be discharged completely.
  2. Next, a known resistor (usually a 10 KΩ Resistor) must be connected in series with the capacitor.
  3. After that, the circuit must be completed by connecting a power supply of known voltage. This circuit is nothing but RC Circuit as shown in the Fig. 4.
  4. Then, the power supply must be turned on and the time taken for the Capacitor to charge to 63.2% of the supply voltage should be measured.
  5. Next, from this Time and Resistance, the Capacitance must be measured and it should be compared with the value printed on the Capacitor. If they are similar or nearly equal, then the Capacitor can be considered as operational. On the contrary, if the difference is significantly large; then the Capacitor should be replaced as it is a dead one.

RC Circuit

Fig. 4 – RC Circuit Used in Capacitor Testing

Capacitor Testing with Voltmeter

  1. At first, the Capacitor must be disconnected from the circuit board and then it should be discharged completely.
  2. Next, the voltage rating on the Capacitor must be observed (usually it is mentioned in as 16V, 25V, 50V etc.) After that, the leads of the Capacitor should be connected to a power supply or a battery but the voltage must be less than the maximum rating.
  3. Next, the Capacitor must be charged for a short period (usually 4-5 seconds) and then it should be disconnected from the power supply.
  4. Then, the Digital Multimeter should be set to DC Voltmeter settings and the voltage across the Capacitor must be measured. The proper terminals of the voltmeter and the capacitor must be connected.
  5. For a good Capacitor, the initial voltage reading on the Multimeter must be close to the supplied voltage. On the contrary, if the difference is large, then the capacitor is regarded as a faulty one.

Capacitor connected to a battery

Fig. 5 – Capacitor Connected to Battery

Capacitor Testing using Analog Multimeter

  1. At first, the Capacitor must be disconnected from the circuit board and then it should be discharged completely.
  2. Next, the Analog Multimeter should be put in Ohmmeter position and if there are several ranges, a higher range must be chosen.
  3. After that, the leads of the Capacitor should be connected to the Multimeter probes and the readings on the Multimeter must be observed.
  4. In the beginning, the resistance will be low and then will gradually increase for a good Capacitor. For a shorted Capacitor, the resistance will low at all times. For an Open Capacitor, there will be either no movement of the needle or the resistance will always show a higher value.

Analog Multimeter

Fig. 6 – Analog Multimeter

Capacitor Testing by Shorting the Leads

  1. At first, the capacitor must be disconnected from the circuit board and then it should be discharged completely.
  2. Next, the leads of the capacitor must be connected to the supply terminal.
  3. After that, the power supply should be switched on for a very short period of time (usually 1 second to 5 seconds) and then it must be switched off. The Capacitor leads; then have to be disconnected from the power supply.
  4. The terminals of the Capacitor should be shorted by using metal contact. This step must be done by taking proper insulating measures.
  5. The condition of the Capacitor can be determined by the spark from the Capacitor. For a Capacitor in good condition, the spark is large and strong. For a bad Capacitor, the spark is small and weak.

Terminals of Capacitor Shorted

Fig. 7 – Terminals of Capacitor Shorted

Advantages of Capacitor Testing

The advantages include:

  • Testing prevents system losses.
  • It might prevent current fluctuations.
  • Helps in improving Power Factor.
Also Read:
What is Voltage Stabilizer - Why we need it, How it works, Types and Applications
How to Choose Battery - Method & Short / Long Term Power Requirements
Microcontroller - Classification, Architecture, Application, Advantage

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