 Home Capacitors  Mar 7 2020

# How to Test a Capacitor with a Multimeter in 5 Ways?

## I Introduction

Two adjacent conductors are sandwiched by a layer of a non-conductive insulating medium to form a capacitor. Capacitors are one of the most commonly used electronic components. They play an important role in circuits like tuning, bypassing, coupling, and filtering. For example, they are often used in the tuning circuit of the transistor radio, coupling circuit and bypass circuit of the color TV.

This article mainly introduces how to properly use multimeters to test capacitors and aluminum electrolytic capacitors, including detailed operating steps, working principles, notice, and explaining some fundamental knowledge about capacitors.

We also have a related post about how to check start capacitors you may be interested in. Dont't miss it!

How to Test Capacitors with a Dgital Multimeter

## Catalog

 I Introduction II Definition of Capacitor III The Reasons and Effects of Testing Capacitors and Withstand Voltage Performance 3.1 Why Should We Measure the Capacitance of A Capacitor? 3.2 Why Should Capacitors Undergo A Withstand Voltage Test? IV The Difference of Capacitors with Different Capacity in Test 4.1 Small-capacity Capacitor Test 4.2 Large-capacity Capacitor Test 4.3 Supercapacitor Test V How to Test Capacitors with A Multimeter? 5.1 Direct Test with A Capacitor 5.2 Test with Resistance File 5.3 Test with Voltage File 5.4 Test with Buzzer 5.5 Use a Digital Multimeter to Measure Capacitance Greater Than 20μF VI How to Detect Capacitors in Aluminum Capacitors 6.1 Appearance Physical Inspection 6.2 Capacity and Loss Test 6.3 Ripple Voltage Test 6.4 Leakage Current Test 6.5 Explosion Test 6.6 Temperature Test VII Considerations for Capacitor Testing VIII One Question Related to Testing Capacitor 8.1 Question 8.2 Answer

## II Definition of Capacitor

Capacitors comprise components that store electricity and electrical energy (potential energy). A conductor is surrounded by another conductor, or the electric field lines emitted by one conductor all terminate in the conduction system of the other conductor, called a capacitor.

## III The Reasons and Effects of Testing Capacitors and Withstand Voltage Performance

### 3.1 Why Should We Measure the Capacitance of A Capacitor?

The purpose of measuring the capacitance value of a capacitor in a general sense of electricity is to check the change of its capacitance value. By comparing the measured value with the value on the nameplate, you can judge whether the internal wiring is correct and whether the insulation has deteriorated because of moisture, whether the component has broken down, and whether oil leakage has caused the capacitance to decrease. So be careful during the substantial operation.

### 3.2 Why Should Capacitors Undergo A Withstand Voltage Test?

The withstand voltage test refers to the test of the capability of withstanding voltage of various electrical devices and structures. The process of applying a high voltage to an insulating material or an insulating structure without damaging the performance of the insulating material is considered a withstand voltage test. Broadly speaking, the primary purpose of the capability of withstanding voltage test is to check the ability of the insulation to withstand working voltage or overvoltage, and then to check whether the insulation performance of the product equipment meets safety standards.capability of withstanding voltage test is to check the ability of the insulation to withstand working voltage or overvoltage, and then to check whether the insulation performance of the product equipment meets safety standards. Figure1. Capacitor Testing

## IV The Difference of Capacitors with Different Capacity in Test

### 4.1 Small-capacity Capacitor Test

The capacitance of a small-capacity capacitor is generally below 1 UF because the capacity is too minor, the charging phenomenon is unobvious, and the angle of the hand to the right is not large when measuring. Therefore, it is generally impossible to estimate its capacitance with a multimeter, but only to detect whether it has leakage or breakdown. Under normal conditions, the resistance value of both ends of the multimeter R × 10 k should be infinite. If the certain resistance value is measured or the resistance value is close to 0, it means that the capacitor has leaked electricity or has been damaged by a breakdown.

### 4.2 Large-capacity Capacitor Test

Large capacity can generally be tested by 1K-10K, see the sweep of the meter during charging, and the resistance value indicated by the last meter. The closer to the left, the better. If the resistance is too small, it cannot be used.

### 4.3 Supercapacitor Test

The method of measuring supercapacitors is completely different from other types of capacitors. Supercapacitors have exceptionally large capacitance values that cannot be measured directly by standard equipment. Ordinary methods for testing the capacitance of these capacitors are by charging the supercapacitors at the rated voltage and discharging the supercapacitors by a constant current load. Figure2. Different Capacitors

## V How to Test Capacitors with A Multimeter?

### 5.1 Direct Test with A Capacitor

Some digital multimeters have the function of measuring capacitance, and their ranges are divided into five ranges of 2,000p, 20n, 200n, 2μ and 20μ. When measuring, you can directly insert the two pins of the discharged capacitor into the Cx jack on the meter board and select the appropriate range to read the display data.

2,000p file, suitable for measuring capacitance less than 2000pF; 20n file, suitable for measuring the capacitance between 2000pF and 20nF; 200n file, suitable for measuring the capacitance between 20nF and 200nF; 2μ file, suitable for measuring between 200nF and 2μF Capacitance; 20μ range, suitable for measuring capacitance between 2μF and 20μF.

Experience has shown that some types of digital multimeters (like DT890B +) allow a considerable error when measuring small-capacity capacitors below 50pF, and there is almost no reference value for measuring capacitance below 20pF. At this time, the small value capacitance can be measured by the series method.

Method: First find a capacitor of about 220pF, use a digital multimeter to measure its actual capacity C1, and then connect the small capacitor to be tested in parallel to measure its total capacity C2. The difference between the two (C1-C2) is subsequently the capacity of small capacitors under test.

It is extremely accurate to measure the small capacitance of 1 ~ 20pF with this method. Figure3. How to Test a Capacitor with a Multimeter

### 5.2 Test with Resistance File

The practice has proved the charging process of capacitors can also be observed by using a digital multimeter, which actually reflects the change of charging voltage in discrete digital quantities. Assuming that the digital multimeter's measurement rate is n times/second, in the process of observing the charging of the capacitor, you can see n readings that are independent of each other and increase sequentially. According to this display characteristic of the digital multimeter, it is possible to detect the quality of the capacitor and estimate the size of the capacitance.

The following describes the method of detecting the capacitor using the resistance meter of a digital multimeter, which is of practical value for instruments without a capacitor. This method is suitable for measuring large-capacitance capacitors from 0.1 μF to several thousand microfarads.

5.2.1 Operation Method of Measurement

As shown in Figure 4, set the digital multimeter to the appropriate resistance level. The red and black test leads respectively to touch the two poles of the capacitor Cx under test. At this time, the displayed value will gradually increase from "000" until the display Overflow symbol "1."If"000" is consistently displayed, it means the capacitor is short-circuited internally; if it is constantly displayed, the internal poles of the capacitor may be open-circuited, or the selected resistance level may be inappropriate. When checking electrolytic capacitors, pay attention to the red test lead (positive charge) is connected to the positive electrode of the capacitor, and the black test lead is connected to the negative electrode of the capacitor. Figure4. Digital Multimeter

5.2.2 Measurement Principle

Figure5 shows the measurement principle of measuring capacitors with resistance files. During the measurement, the positive power source charges, the capacitor Cx to be measured through the standard resistor R0. At the moment when charging starts, Vc = 0, so “000” is displayed. As Vc gradually increases, the displayed value increases. When Vc = 2VR, the meter starts to display the overflow symbol "1." The charging time t is the time required for the displayed value to alter from "000" to overflow. This time interval can be measured with a quartz meter. Figure5. Principle of Measurement

5.2.3 Measured Data Using DT830 Digital Multimeter to Estimate Capacitance

The principle of selecting the resistance range is: when the capacitance is small, a high resistance should be selected, and when the capacitance is large, a low resistance should be selected. If you use a high-resistance range to estimate a large-capacity capacitor, the measurement time will last a long time because the charging process is very slow. If you use a low-resistance range to check a small-capacity capacitor, the meter will always show an overflow because the charging time is extremely short, and you cannot see the change.

### 5.3 Test with Voltage File

Detecting capacitors with the DC multimeter of a digital multimeter is actually an indirect measurement method. This method can measure small-capacitance capacitors from 220pF to 1μF, and can accurately measure the capacitor leakage current.

5.3.1 Measurement Methods and Principles

The measurement circuit is shown in Figure6. E is an external 1.5V dry battery. Set the digital multimeter to the DC 2V range, connect the red test lead to one electrode of the capacitor Cx under test, and the black test lead to the battery negative. The input resistance of the 2V range is RIN = 10MΩ. After the power is turned on, battery E charges Cx via RIN and starts to establish voltage Vc. The relationship between Vc and charging time t is Figure6. Wiring Diagram of Measuring Capacitor with Voltage Block

Here, because the voltage across RIN is the instrument input voltage VIN, so RIN actually has the function of a sampling resistor. obviously,

VIN (t) = E-Vc (t) = Eexp (-t / RINCx) (5-2)

Figure7 is the change curve of the input voltage VIN (t) and the charging voltage Vc (t) on the capacitor under test. It can be seen from the figure that the change process of VIN (t) and Vc (t) is just the opposite. The curve of VIN (t) decreases with time, while Vc (t) increases with time. Although the meter shows the change process of VIN- (t), it indirectly reflects the charging process of the capacitor Cx under test. During the test, if Cx is open (no capacity), the displayed value will always be “000”. If Cx is internally short-circuited, the displayed value will always be the battery voltage E and will not change with time. Figure7. Change Curve of VIN (t) and Vc (t)

Equation (5-2) shows that when the circuit is turned on, t = 0, VIN = E, the initial display value of the digital multimeter is the battery voltage, and then as Vc (t) increases, VIN (t) gradually decreases. Until VIN = 0V, the Cx charging process ends, at this time

Vcx (t) = E

Using digital multimeter voltage level detection capacitor, not only can check small-capacitance capacitors from 220pF to 1μF, but also measure the capacitor leakage current. Let the leakage current of the capacitor being measured be ID, and the stable value displayed by the meter at the end is VD (the unit is V), then Figure8. Equation (5-3)

5.3.2 Examples

Example 1:

The measured capacitance is a 1μF / 160V fixed capacitor, using the 2VDC range of the DT830 digital multimeter (RIN = 10MΩ). Connect the circuit according to Figure6. Initially, the meter displayed 1.543V, and then the displayed value gradually decreased. After about 2 minutes, the displayed value stabilized at 0.003V. Find the leakage current of the capacitor under test. Figure9. Equation

The leakage current of the capacitor under test is only 0.3nA, indicating good quality.

Example 2:

The capacitor under test is a 0.022μF / 63V polyester capacitor. The measurement method is the same as in Example 1. Due to the small capacity of this capacitor, VIN (t) decreases rapidly during measurement, and after about 3 seconds, the displayed value decreases to 0.002V. Substituting this value into equation (5-3), the leakage current was calculated to be 0.2nA.

5.3.3 Notes

(1) Before measurement, the two pins of the capacitor should be short-circuited and discharged, otherwise the change process of the reading may not be observed.

(2) Do not touch the capacitor electrode with both hands during the measurement to avoid meter jumping.

(3) During the measurement, the value of VIN (t) changes exponentially, and it decreases rapidly at the beginning. With the increase of time, the decline rate will become slower and slower. When the capacitance of the capacitor Cx under test is less than a few thousand picofarads, because VIN (t) initially drops too quickly, and the meter's measurement rate is too low to reflect the original voltage value, the initial display value of the meter is lower than the battery Voltage E.

(4) When the measured capacitor Cx is greater than 1 μF, in order to shorten the measurement time, a resistance file can be used for measurement. However, when the capacitance of the capacitor under test is less than 200pF, it is difficult to observe the charging process because the change in the reading is very short.

### 5.4 Test with Buzzer

Using the buzzer file of the digital multimeter, you can quickly check the quality of the electrolytic capacitor. The measurement method is shown in Figure10. Set the digital multimeter to the buzzer position, and use two test leads to contact the two pins of the capacitor Cx under test. A short beep sound should be heard, the sound will stop, and the overflow symbol "1" will be displayed. Then, measure the two test leads again, and the buzzer should sound again, and the overflow symbol “1” will be displayed at last, which indicates that the electrolytic capacitor under test is basically normal. At this time, you can dial to 20MΩ or 200MΩ high resistance to measure the leakage resistance of the capacitor to determine its quality. Figure10. Wiring Diagram For Testing Electrolytic Capacitor with Buzzer

The principle of the above measurement process is: At the beginning of the test, the charging current of the instrument to Cx is large, which is equivalent to the path, so the buzzer sounds. As the voltage across the capacitor continues to increase, the charging current rapidly decreases, and finally the buzzer stops sounding.

During the test, if the buzzer keeps sounding, it means that the internal of the electrolytic capacitor has been short-circuited. If the buzzer keeps sounding and the meter always shows "1" when the meter pen is repeatedly measured, it means that the capacitor under test is open or the capacity disappears.

### 5.5 Use a Digital Multimeter to Measure Capacitance Greater Than 20μF

For common digital multimeters, the maximum measurement value of the capacitance file is 20 μF, which sometimes cannot meet the measurement requirements. For this reason, the following simple method can be used to measure the capacitance of more than 20μF with the capacitance file of the digital multimeter, and the maximum capacitance of several thousand microfarads can be measured. When using this method to measure large-capacitance capacitors, there is no need to make any changes to the original digital multimeter circuit.

The measurement principle of this method is based on the formula C string = C1C2 / (C1 + C2) of two capacitors in series. Since two capacitors with different capacities are connected in series, the total capacity after the series connection is smaller than that of the capacitor with the smaller capacity. Therefore, if the capacity of the capacitor to be measured exceeds 20 μF, only one capacitor with a capacity of less than 20 μF is used. In series with it, you can measure directly on the digital multimeter.

According to the formula of two capacitors in series, it is easy to derive C1 = C2C string / (C2-C string). Using this formula, the capacitance value of the measured capacitor can be calculated. Here is a test example to illustrate the specific method of using this formula.

The component under test is an electrolytic capacitor with a nominal capacity of 220 μF, and is set to C1. Select an electrolytic capacitor with a nominal value of 10μF as C2, use a digital multimeter 20μF capacitor to measure the actual value of this capacitor as 9.5μF, and connect the two capacitors in series to measure the C string as 9.09μF. Substituting C2 = 9.5 μF and C string = 9.09 μF into the formula, then

C1 = C2C string / (C2-C string) = 9.5 9.09 / (9.5-9.09) ≈211 (μF) Figure11. Digital Multimeter

Note: No matter how much the capacity of C2 is selected, a capacitor with a larger capacity must be selected under the premise of less than 20μF, and C2 in the formula should be substituted into the actual measured value instead of the nominal value, which can reduce errors. The two capacitors are connected in series and measured with a digital multimeter. Due to the capacitance error and measurement error of the capacitor itself, as long as the actual measured value is close to the calculated value, the capacitor C1 to be measured is considered good. capacity.

In theory, this method can measure capacitance of any capacity, but if the capacity of the capacitor under test is too large, the error will increase. The error is proportional to the size of the capacitor to be measured.

## VI How to Test Aluminum Electrolytic Capacitors

### 6.1 Appearance Physical Inspection

(1) First check whether the capacitor under test has a formal "Product Specification", which includes the product name, specifications, installation dimensions, process requirements, technical parameters, and supplier name, address and contact information to ensure this. Batch products are provided by regular manufacturers. The logo on the capacitor should include the trademark, working voltage, standard capacitance, polarity, and operating temperature range.

(2) Refer to the process parameters in the “Product Specification” and observe whether the appearance, color, and material of the capacitor are consistent with the process indicators marked on it.

(3) Use a vernier caliper to confirm the installation size of the capacitor to ensure that the diameter, height, and diameter and spacing of the lead-out terminal are within the tolerance of the product process, and the external dimensions must meet the company's selection requirements.

(4) Check the appearance of the capacitor to ensure its appearance is neat, without obvious deformation, breakage, cracks, spots, dirt, rust, etc., and its marking is clear, firm, correct and complete.

(5) Check the lead-out terminals to ensure that their terminals are straight, free from oxidation, rust, and have no effect on their conductive properties, and that the lead-out terminals are free of distortion, deformation, and mechanical damage that affects insertion and removal.

(6) Check that the production date marked on the electrolytic capacitor should not exceed six months, and make a record. Figure12. Aluminum Electrolytic Capacitor

### 6.2 Capacity and Loss Test

(1) Use the electric bridge to test whether the actual capacity is consistent with the nominal capacity (the electrolytic capacitor generally has an error range of ± 20%). The loss tangent value tanθ (that is, the D value) is in compliance with the standard.

(2) How to use the Zen tech bridge tester: After connecting the power supply correctly, press the "POWER" key to turn on the tester's working voltage; press the "LCR" key to select the test type (L: Inductance, C: Capacitance, R: resistance).

(3) Press the "UP" and "DOWN" keys to select the test range (μF, nF, pF) and press the "FREQ" key to select the test frequency (100HZ,

(120HZ, 1KHZ) can choose the required test frequency according to the technical parameters provided by the manufacturer, the test in this article selects "100HZ".

(4) Press "SERIES" (parallel) and "PARALLEL" (parallel) to select the connection mode for the test, small capacitance (less than 10μF)

To use parallel mode, use large mode (10μF and above) in series mode.

(5) After the setting is completed, connect the bridge test ports ("LOW" and "HIGH") to the two ends of the capacitor, and use the label paper to record the capacity value and loss value on the display respectively. And attach the label paper to the corresponding capacitor for subsequent analysis.

### 6.3 Ripple Voltage Test

(1) Connect the circuit as shown below, and connect the capacitor to be tested to the adjustable DC power supply (note that the positive and negative poles are not connected reversely). Connect the positive electrode of the oscilloscope probe with a non-inductive capacitor (1μF 1200V.DC) in series to the positive electrode of the capacitor to be tested. Figure13. Circuit of Ripple Voltage Test

(2) For the setting of the oscilloscope, it must be set to the DC test position first, and the fine adjustment knob of the oscilloscope voltage must be locked.

(3) During the test, the DC voltage should be slowly increased to the rated voltage with a voltage regulator, and the changes displayed by the oscilloscope should be closely monitored. The correct range should be selected to ensure that the voltage can be accurately read from the oscilloscope waveform .

(4) Take the ripple waveform with the camera, and record the range and division of the oscilloscope with label paper (that is, calculate the ripple voltage and paste it on the corresponding capacitor for subsequent analysis and comparison.

(5) After the recording is completed, disconnect the DC power supply, discharge the capacitor under test and the non-inductive capacitor with the bulb load, and then remove the capacitor under test from the test bench.

### 6.4 Leakage Current Test

6.4.1 Indirect Measurement Method One

Connect as shown below. Connect a 1K resistor in series with the capacitor under test and connect it to a DC adjustable power supply. Use an oscilloscope probe to connect to both ends of the resistor. Indirectly calculate the leakage current of the capacitor to be measured by sampling the voltage signal across the resistor.

Operating essentials and precautions: After the circuit is connected, adjust the DC adjustable power supply to the rated voltage of the capacitor. After the circuit is equilibrated for two minutes, read the voltage value across the resistor. When reading the oscilloscope, the voltage trimming knob should be locked. Record the maximum value of the voltage waveform as the voltage value and divide it by the resistance value to obtain the value of the leakage current. The current is too large and the resistor is burned out. After the test, the capacitor should be discharged and then removed to avoid accidents. Figure14. Circuit

6.4.2 Indirect Measurement Method Two

Connect the wiring as shown in the figure, and add an air switch in series between the capacitor and the DC power supply. First close S1 and S2 respectively, and adjust the voltage regulator to the rated voltage to charge the capacitor for two minutes. Figure15. Circuit

After that, both S1 and S2 are disconnected. At this time, the adjustable power supply is at the rated value. Do not move. Add a milliamp meter between S1 and S2, as shown in the figure below: S1 and S2 are both closed, and the leakage current can be directly read through the milliamp meter after one minute of stabilization. Figure16. Circuit

6.4.3 Precautions

Remember not to connect the milliamp meter to the line directly when the capacitor is not charged, because the initial charging current is large, the milliamp meter will be burned out by accident. In the disassembly process, first discharge the capacitor with the bulb load. When discharging, remove the milliamp meter first, and ensure that the discharge current does not pass the test resistor to prevent damage to the test resistor and the millimeter meter.

6.4.4 Leakage Current at 1.2Un

Adjust the DC voltage to 1.2 times the rated voltage of the electrolytic capacitor, measure its leakage current again and compare different samples.

### 6.5 Explosion Test

6.5.1 DC Test

Apply reverse DC voltage to the capacitor under test, slowly adjust the adjustable DC voltage, and observe the current closely with a clamp meter.The DC power setting is generally not more than 30V. The current value is set according to the size of the capacitor as follows:

When the capacitor diameter is 6mm ≤ 22.4mm, the current cannot exceed 1A; when the capacitor diameter is> 22.4mm, the current cannot exceed 10A.

6.5.2 Observe The Surface Temperature of The Capacitor

During the experiment, use a thermometer to closely observe the surface temperature of the capacitor (the sensing contact of the thermometer can be wrapped around the capacitor with tape). Note that the initial current is very small and almost zero. When the temperature of the capacitor rises (about 35-40 ° C) The current is significantly increased. At this time, close observation should be made. When the current reaches or approaches 10A, the voltage should be lowered to ensure that the current is controlled within 10A.

6.5.3 Capacitor Safety Valve

Within 30 minutes after the start of the test, the capacitor safety valve should be opened. If the capacitor fuse is open, the power should be cut off immediately (the electrolytic capacitor of 350V 6800F will automatically open under the following conditions, the current is about 8A, the surface temperature is about 45-60 ° C.), If the current is close to 10A and the fuse is still 30 minutes later, If it is not turned on, this function is missing. Figure17. DC Digital Voltmeter

### 6.6 Temperature Test

The capacity of a capacitor will change due to different ambient temperatures. In general, the capacity will increase as the temperature rises. The temperature test is to test the change of capacitance after equilibration under the set temperature.

6.6.1 High Temperature Test

(1) Connect two small wires to the lead-out terminal of the capacitor to be tested respectively, and test the capacity of the two lead terminals at normal temperature, and label them for record.

(2) Put the capacitor into the high and low temperature alternating humidity and heat test box, and leave the leads outside the test box to test the capacitance.

(3) Turn on the test box switch button, click "Temperature Setting" on the screen, set the temperature to 100 ° C, and click "Run" to start the test box.

(4) Test the capacity again about 2 hours after the temperature reaches 100 ° C, and calculate the percentage change in capacity (the initial measurement of the difference).

6.6.2 Low Temperature Test

(1) Put the capacitor to be tested into the test box (be careful not to use capacitors that have been tested at high temperatures, except for special needs).

(2) Turn on the test box switch button, click "temperature setting" on the screen, set the temperature to -25 ° C, and click "run".

(3) Test the capacity again about 2 hours after the temperature reaches -25 ° C, and calculate the percentage change in capacity (the initial measurement of the difference).

6.6.3 Precautions

The test should pay close attention to whether there is any obvious change in the capacitor. If serious conditions such as cracking of the capacitor surface and opening of the safety valve occur, the test box should be stopped immediately. During the test, the operating procedures of the test box should be strictly followed, and the door of the test box should not be opened at will. At the end of the high temperature test, the capacitor can only be taken out after the temperature inside the test box has dropped to prevent accidents such as burns. Figure18. Capacitors

## VII Considerations for Capacitor Testing

(1) When measuring with a multimeter, select the gear according to the rated voltage of the capacitor. For example, the capacitor voltage commonly used in electronic equipment is low, only a few volts to dozens of volts. If the multimeter RX10k is used for measurement, the battery voltage in the meter is 12 ～ 22.5V, which is likely to cause capacitor breakdown. Therefore, the RXlk file should be used. measuring.

(2) For the capacitor just removed from the line, be sure to discharge the capacitor before measurement to prevent the residual charge in the capacitor from being discharged to the meter and damage the meter.

(3) For capacitors with high working voltage and large capacity, the capacitors should be sufficiently discharged, and the operator should have protective measures to prevent electric shocks during discharge.

### 8.1 Question

What should we do when checking a capacitor with an ohm meter？

To remove the capacitor from the circuit.

It's usually easy to remove a start or run capacitor – you simply unhook it from its harness and disconnect the wires. However, be careful to avoid touching the capacitor terminals. If the capacitor isn't dead, it might have a full charge, and if so, you could get a serious shock.

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#### 1 comment

• • Jagdish Patel on 2020/7/12 12:42:42

How can check 13000 μF 150 VDC Made in USA ?