How to test a capacitor with a multimeter for functionality

What is a capacitor

A capacitor is an electrical element that is capable of storing a certain electrical charge. The main parameter of the element is the capacitance, which is calculated in farads. 1 farad is quite a large value. Modern capacitors have the following capacitance designations:

• picofarad is denoted pF or pF;
• nanofarad is denoted nF or nF;
• microfarad is denoted mF or mF.

The principle of operation of the device is quite simple. The operation and delivery of a pulse differs only from the current in the circuit to which it is connected.

Characteristics

As an element of an electrical circuit, a capacitor has the following parameters:

• Electric capacitance, which is characterized by the property of accumulating electric charge.
• Rated voltage. The voltage value on the plates at which the element retains its parameters during its service life.

When working with electrical circuits, it is necessary to take into account parasitic parameters that are undesirable:

• Leakage current, which appears due to the imperfection of the dielectric and the quality of the insulation of the plates.
• Series equivalent resistance, which consists of the resistance of the leads, the resistance of the lead-plate contact, and the internal properties of the dielectric.
• Equivalent inductance, which includes the inductance of the leads and plates.
• Dielectric loss tangent, characterizing electrical losses in a capacitor at high frequencies.
• The temperature coefficient of a capacitance, showing how it changes with temperature.
• Parasitic piezoelectric effect, manifested as the generation of voltage during physical impact on the dielectric (shaking, vibration).

Equivalent circuit

It's better to check first

First, this element needs to be de-energized. It is clear that there is no need to deprive it of its power source. It is enough to turn off the electrical appliance and disconnect the plug from the socket. If you approach this issue radically, then for safety you can turn off all the circuit breakers at the switchboard that are responsible for supplying electricity to the room.

Now we need a special device - a multimeter - to find out whether the capacitor is charged.

1. Select the mode for measuring DC voltage (direct current).
2. We set the device knob to the maximum voltage measurement level.
3. We connect the multimeter probes to the contacts of the electronic component. As a rule, two rods protrude from it. It is to them that you need to connect both probes of the detector. You need to press firmly enough so that digital readings appear on the device display. It makes no difference which probe goes to which contact. The resulting value will be the same in both cases.

We need to understand what voltage is at the terminals of the element. Depending on the indications, the discharge method is selected:

1. If the reading is less than 10 volts, there is no need to discharge.
2. If the display shows measurements between 10–99 volts, you can discharge it with a screwdriver.
3. If values ​​are 100 volts or higher, it is recommended to use a discharge device.

Capacitor device

The simplest capacitor consists of two metal plates (plates) separated by a dielectric layer. Capacitance (the ability to accumulate electrical charge) increases with increasing plate area and decreasing thickness of the insulating layer.

The parameters of the simplest design are too small. There are two ways to increase it:

• An increase in the area of ​​the plates, which leads to an increase in dimensions.
• Reducing the thickness of the dielectric, leading to a decrease in the rated operating voltage due to electrical breakdown.

In order to avoid these problems, special designs have been developed. For example, if you make plates of small width and long length, they can be rolled together with a flexible dielectric into a dense cylinder, resulting in a cylindrical capacitor. By placing the dielectric plates alternately, in the form of a layer cake, and alternating connections to the terminals, a rectangular component with a large effective plate area is obtained.

Different types of construction

Another way is to use a thin oxide layer on the surface of a metal foil as a dielectric and a conducting electrolyte solution as a second plate. This produces an electrolytic capacitor whose design has the largest capacity.

Important! Such devices have the disadvantage of maintaining the polarity of the connection, which limits their use: it is only possible in DC circuits as smoothing filters.

AC circuit

In an AC circuit, a capacitor is a resistance. It quickly accumulates a certain charge and gradually releases it. Accumulation and full release occurs during a change in the electric wave.

DC circuit

In a DC circuit, charge accumulates on the plates, increasing the potential difference across the plates. The potential difference increases to the voltage value. As soon as it becomes equal to the voltage, the common circuit is broken.

Types of capacitors

To start powerful compressor engines, oil-filled non-polar capacitors are used.

The housing is filled with oil inside for good heat transfer to the surface of the housing. The body is usually metal or aluminum. The most affordable capacitors of this type are CBB65.

To start less powerful loads, such as fan motors, dry capacitors are used, the housing of which is usually plastic.

The most common capacitors of this type are CBB60, CBB61.

The terminals are double or quadruple for ease of connection.

Capacitor charge. Current

In terms of its purpose, a capacitor resembles a battery, but it is still very different in its operating principle, maximum capacity, and charging/discharging speed.

Let's consider the principle of operation of a flat-plate capacitor. If you connect a power source to it, negatively charged particles in the form of electrons will begin to collect on one plate of the conductor, and positively charged particles in the form of ions will begin to collect on the other. Since there is a dielectric between the plates, charged particles cannot “jump” to the opposite side of the capacitor. However, electrons move from the power source to the capacitor plate. Therefore, electric current flows in the circuit.

At the very beginning of connecting the capacitor into the circuit, there is the most free space on its plates. Consequently, the initial current at this moment encounters the least resistance and is maximum. As the capacitor fills with charged particles, the current gradually drops until the free space on the plates runs out and the current stops completely.

The time between the states of an “empty” capacitor with a maximum current value, and a “full” capacitor with a minimum current value (i.e., its absence), is called the transition period of the capacitor charge.

What is capacity

If you remove a single electrical conductor infinitely far, eliminating the influence of charged bodies on each other, then the potential of the remote conductor will become proportional to the charge. But conductors of different sizes do not have the same potential.

The SI unit of capacitance for a capacitor is the farad. The proportionality coefficient is denoted by the letter C - this is the capacitance, which is affected by the size and external structure of the conductor. The material and phase state of the electrode substance do not play a role - the charges are distributed on the surface. Therefore, in the international GHS rules, capacity is measured not in farads, but in centimeters.

A solitary sphere with a radius of 9 million km (1400 Earth radii) contains 1 farad. A separate conductive element holds charges in quantities insufficient for technical use. According to technologies of the 21st century. a capacitance of capacitors with units of measurement higher than 1 farad is created.

A structure of at least 2 electrodes and a separating dielectric is capable of accumulating the amount of electricity required for the operation of electronic circuits. In this design, positive and negative particles are mutually attracted and support themselves. The dielectric between the electron-positron pair does not allow annihilation. This state of charge is called bound.

Previously, bulky equipment that was not very accurate was used to measure electrical quantities. Now even a novice radio amateur knows how to measure capacitance with a tester.

Syntax

For XMPP client users, use the command

fiz keys

where the keys are known parameters, parameters=value, separated by semicolons

The key key=razryad is required when calculating the capacitor discharge

and zaryad when calculating the charge

Since with other key parameters completely different formulas will be calculated. For example, ballistic motion or pressure above sea level.

Notice how this calculator differs from others:

Firstly: data can be entered without converting from nanoFarads to Farads, and kiloOhms to Ohms. If the parameters are set in units of measurement, then write that way. If you do not write it, it is considered that the data is given in basic SI units (i.e. meter, Farad, Ohm)

Secondly: The calculation is carried out according to those parameters that can be calculated knowing the original ones. This is very convenient when you need to calculate any of the parameters in the formula when all the others are known. Other well-known calculators can only calculate using a certain algorithm and only in one direction.

Markings on capacitors

Knowledge of the characteristics of electronic devices is required for accurate and safe operation.

Determining the capacitance of a capacitor involves measuring the value with instruments and reading the markings on the case. The indicated values ​​and those obtained during measurements differ. This is caused by imperfect production technologies and operational variations in parameters (wear, temperature influence).

The body indicates the nominal capacity and parameters of permissible deviations. In household devices, devices with a deviation of up to 20% are used. In the space industry, military equipment and automation of dangerous objects, a spread of characteristics of 5-10% is allowed. Work plans do not contain tolerance values.

The rated capacity is coded according to IEC standards - the International Electrotechnical Commission, which unites national standards organizations in 60 countries.

The IEC standard uses the notation:

1. 3 digit encoding. 2 signs at the beginning - the number of pF, the third - the number of zeros, 9 at the end - the value is less than 10 pF, 0 at the front - no more than 1 pF. Code 689 - 6.8 pF, 152 - 1500 pF, 333 - 33000 pF or 33 nF, or 0.033 µF. To make it easier to read, the decimal point in the code is replaced by the letter "R". R8=0.8 pF, 2R5 - 2.5 pF.
2. 4 digits in marking. The last one is the number of zeros. The first 3 are the value in pF. 3353 - 335000 pF, 335 nF or 0.335 µF.
3. Using letters in code. The letter µ is μF, n is nanofarad, p is pF. 34p5 - 34.5 pF, 1µ5 - 1.5 µF.
4. Planer ceramic products are coded with the letters AZ in 2 registers and a number indicating the power of 10. K3 - 2400 pF.
5. Electrolytic SMD devices are marked in 2 ways: numbers - the rated capacity in pF and next to it or in the 2nd line if there is space - the value of the rated voltage; a letter encoding the voltage and next to it there are 3 numbers, 2 determine the capacity, and the last one - the number of zeros. A205 means 10 V and 2 µF.
6. Surface mount products are marked with a code of letters and numbers: CA7 - 10 µF and 16 V.
7. Encodings - by body color.

Determining the capacitance of an unknown capacitor

Method: measuring capacitance with special devices

The easiest way is to measure the capacitance using a device that has a capacitance measurement function. This is already clear, and this was already discussed at the beginning of the article and there is nothing more to add.

If you're not very comfortable with instruments, you can try putting together a simple homemade tester. You can find good schemes on the Internet (more complex, simpler, very simple).

Well, or finally fork out for a universal tester that measures capacitance up to 100,000 µF, ESR, resistance, inductance, allows you to check diodes and measure the parameters of transistors. How many times has he helped me out!

Calculation using formulas

Calculation of the nominal capacity of an element is required in 2 cases:

1. Electronic equipment designers calculate the parameter when creating circuits.
2. In the absence of capacitors of suitable power and capacity, craftsmen use element calculations to select from available parts.

RC circuits are calculated using the value of impedance - complex resistance (Z). Ra - current losses due to heating of circuit participants. Ri and Re — take into account the influence of inductance and capacitance of the elements. At the resistor terminals in the RC circuit, the voltage Uр is inversely proportional to Z.

Thermal resistance increases the potential across the load, and reactive resistance decreases. Operating a capacitor at frequencies above resonant frequencies, when the reactive component of the complex resistance increases, leads to voltage losses. The resonance frequency is inversely proportional to the ability to accumulate charge. From the formula for determining Fр, they calculate what values ​​of C (capacitor capacitance) are required for the operation of the circuit.

To calculate pulse circuits, the circuit time constant is used, which determines the effect of RC on the pulse structure. If the circuit resistance and capacitor charging time are known, the capacitance is calculated using the time constant formula. The truth of the result is influenced by the human factor.

Craftsmen use parallel and series connections of capacitors. The calculation formulas are the reverse of the formulas for resistors. A series connection makes the capacitance smaller in the connection of elements; a parallel circuit adds up the values.

Electromechanical analogies

In the previous leaflet about self-induction, we noted the analogy between inductance and mass. Now we can establish several more correspondences between electrodynamic and mechanical quantities.

For a spring pendulum we have a relationship similar to (1):

(2)

Here, as you already understood, is the spring stiffness, is the mass of the pendulum, and is the current values ​​of the coordinates and speed of the pendulum, and is their greatest values.

Comparing equalities (1) and (2) with each other, we see the following correspondences:

(3)

(4)

(5)

(6)

Based on these electromechanical analogies, we can foresee a formula for the period of electromagnetic oscillations in an oscillatory circuit.

In fact, the period of oscillation of a spring pendulum, as we know, is equal to:

In accordance with analogies (5) and (6), here we replace mass with inductance, and stiffness with inverse capacitance. We get:

(7)

Electromechanical analogies do not fail: formula (7) gives the correct expression for the period of oscillations in the oscillatory circuit. It's called Thomson's formula

. We will present its more rigorous conclusion shortly.

Difficulties of verification

The process of determining the capacitance of a capacitor directly on the board is complicated by the presence of other circuit components - they distort the readings of the device.

First of all, this applies to elements with low resistance to direct current: fuses, inductors, transformer windings. Determining the capacitance of a capacitor without soldering is possible only in the absence of the mentioned components. Semiconductor devices - diodes and transistors - also have an effect.

When checking a capacitor for breakdown by measuring resistance, the multimeter will display the resistance of the Pn junction instead of infinity (on the display “1”). As a result, the state of the capacitor will remain unknown.

Capacitor field energy

All the energy of a charged capacitor is concentrated in the electric field between its plates. The energy stored in a capacitor can be determined as follows. Let's imagine that we do not charge the capacitor immediately, but gradually, transferring electrical charges from one plate to another.

When transferring the first charge, the work done by us will be small. We will spend more energy on transferring the second charge, since as a result of transferring the first charge between the plates of the capacitor there will already be a potential difference that we will have to overcome, the third, fourth and in general each subsequent charge will be more and more difficult to transfer, i.e. moving them will require more and more energy. Let us transfer in this way a certain amount of electricity, which we will denote by the letter Q.

• 
  Current through capacitor

All the energy we expended when charging the capacitor will be concentrated in the electric field between its plates. We denote the voltage between the plates of the capacitor at the end of the charge with the letter U.

As we have already noted, the potential difference during the charging process does not remain constant, but gradually increases from zero - at the beginning of the charge - to its final value U.

To simplify energy calculations, let’s assume that we transferred the entire electric charge Q from one capacitor plate to another, not in small portions, but all at once. But at the same time, we must assume that the voltage between the capacitor plates was not zero, as at the beginning of the charge, and not U, as at the end of the charge, but was equal to the average value between zero and U, i.e. half U. Thus, the energy , stored in the electric field of the capacitor, will be equal to half the voltage U multiplied by the total amount of electricity transferred Q.

We can write the result obtained in the form of the following mathematical formula:

W = UQ/2 (1)

If the voltage in this formula is expressed in volts, and the amount of electricity in coulombs, then the energy W will be obtained in joules. If we remember that the charge accumulated on the capacitor is equal to Q = CU, then formula (1) can be written finally in the following form:

W = CU2/2 (2)

Expression (2) tells us that the energy concentrated in the field of the capacitor is equal to half the product of the capacitance of the capacitor and the square of the voltage between its plates.

This conclusion is very important when studying the section of radio engineering on oscillatory circuits

Related materials:

• Electrical capacity
• Capacitor capacity
• Types of capacitors
• Capacitor designation
• Connection of capacitors

Check Features

The capacitor is checked for serviceability using various methods. The main method is by desoldering it from the circuit. Sometimes you can check the functionality without soldering. But the results of the study will not be accurate - it is influenced by other components. To check the circuit, testers with tiny voltages on the probes are used. Low voltage prevents damage to other components of the board.

Regardless of the features of the models, all electrolytic capacitors have high power. When the test is performed, they are recharged. Its duration is only a few seconds. During the charging process, an increase in the resistance level is observed, with the movement of the tester needle or a change in the digital indicators in the electronic multimeter.

Polar capacitors

These electrolytic conductors are polarized. When connecting to the network, it is necessary to check the correct connection. We connect pluses with pluses, and minuses with minuses. Ignoring this rule leads to an explosion of the electrolyte.

Electrolyte can be solid or liquid. The capacitance of the elements is 0.1–100000 μF. The purpose of the elements is signal alignment and filtering. Marks “-” and “+” are marked on the body. The positive lead is longer. When the polarity is reversed, a breakdown of the dielectric occurs, as a result of which the electrolyte instantly evaporates and the housing ruptures. The dielectric is paper impregnated with electrolyte. Modern buildings are pressed in at the top and cut with a cross.

During an explosion, not the whole thing disintegrates, but only the upper part. Taking into account the specially weakened elements, in the event of a malfunction, swelling of the upper part is visible.

Non-polar capacitors

It is easy to visually distinguish non-polar from polar - it will not have polarity markings on the body. Non-polar ones have a different dielectric material. Consists of ceramics or glass. The self-discharge current is much lower, given the higher dielectric resistance than paper. The higher the resistance of the dielectric partition, the lower the leakage current.

It is not at all necessary to observe polarity when connecting to the circuit. Sometimes such conductors are made very small and included in the circuit in large quantities.

The capacity of the parts is small - from microfarads to picofarads.

Polar and non-polar capacitors

It is very important to separate capacitors into polar and non-polar .

Oxide-based devices: electrolytic aluminum and tantalum are usually polar, which means that if their polarity is reversed, they will fail. Moreover, this failure will be accompanied by violent electrochemical reactions up to the explosion of the capacitor.

Polar capacitors are always marked. As a rule, on electrolytic capacitors, the negative terminal (cathode) is marked with a contrasting stripe on the case; for tantalum capacitors (in yellow rectangular cases), the positive terminal (anode) is marked with a stripe. If you have doubts about the marking, it is better to find the documentation for this capacitor and make sure.

Non-polar capacitors can be connected to the circuit in any direction. For example, multilayer ceramic capacitors are non-polar.

How to test a capacitor with a multimeter

The industry produces several types of testing equipment for measuring electrical parameters. Digital ones are more convenient for measurements and give accurate readings. Arrow people prefer the visual movement of arrows.

If the conder appears to be absolutely intact, it is impossible to check it without instruments. It is better to carry out the check by desoldering it from the circuit. This way the indicators are read more accurately. Simple parts rarely fail. Dielectrics are often damaged mechanically. The main characteristic during testing is the passage of only alternating current. The constant passes exclusively at the very beginning for a short period of time. The resistance of the part depends on the existing capacitance.

The prerequisite for testing a polar electrolytic capacitor with a multimeter for performance is a capacity of more than 0.25 μF. Step-by-step verification instructions:

1. Discharging the element. To do this, its legs are short-circuited with a metal object. A short circuit is characterized by the appearance of a spark and sound.
2. The multimeter switch is set to the resistance value.
3. Touch the legs of the capacitor with the probes, taking into account the polarity. Red to the positive leg, black to the negative leg. This is only necessary when working with a polarized device.

The capacitor begins to charge when the probes are connected. Resistance rises to its maximum. If the multimeter beeps when the probes are zero, it means a short circuit has occurred. If the value 1 is immediately displayed on the dial, then there is an internal break in the element. Such conductors are considered faulty - a short circuit and a break inside the element cannot be repaired.

If the value 1 appears after some time, the element is considered normal.

Testing a non-polar capacitor is even easier. On the multimeter we set the measurement to megaohms. After touching the probes, we look at the readings. If they turn out to be less than 2 MΩ, the part is faulty. More than that - serviceable. There is no need to observe polarity.

Electrolytic

As the name suggests, electrolytic conductors in an aluminum case are filled with electrolyte between the plates. The dimensions are very different - from millimeters to tens of decimeters. Technical characteristics can exceed those of non-polar ones by 3 orders of magnitude and reach large values ​​- units of mF.

In electrolytic models, an additional defect appears associated with ESR (equivalent series resistance). This indicator is also abbreviated ESR. Such capacitors in high-frequency circuits filter the carrier signal from parasitic signals. But it is possible to suppress EMI by greatly reducing the level and playing the role of a resistor. This leads to overheating of the part structure.

How to check without desoldering

It is possible to ring the capacitor with a multimeter without desoldering. For such a check, we select a working specimen with similar characteristics and solder it into the circuit parallel to the one being tested. The working device will indicate a problem in the first element. The method is not applicable to high voltage circuits.

You can check a powerful starting capacitor with a multimeter without desoldering for the presence of a spark. The charged conductor is closed with a screwdriver or other tool with an insulated handle. A characteristic sound with a spark will indicate the functionality of the device.

It is not advisable to take measurements without special instruments. It is easy to get an electric shock on high-voltage samples, and the exact values ​​cannot be determined.

First way

The first method is the simplest. The subject is checked by a tester and called with a multimeter. The device is put into resistance testing mode. It is also worth considering polarity. The multimeter probes are connected to the terminals of the capacitor and the resistance is measured. It is worth considering that the obtained value has no practical use, since it may be an indication of another element. In this way, you can check the capacitive part for a short circuit. If the values ​​on the display begin to increase gradually, then the printed part is being charged by the tester and is in good condition.

Second way

The second method requires soldering a capacitor with the same values ​​into the circuit next to the element under test. Soldering must be done in parallel. Both elements are measured on a de-energized board.

Important! Without soldering, you can only test parts that are part of low-voltage circuits. For high-voltage circuits, such testing is prohibited.

Third way

A situation often arises when there are several capacitors on the board, and it is very difficult to determine which one is faulty. Soldering each one is quite labor-intensive; they often fail when heated. In order to check without desoldering, it is necessary to measure the output voltage. It must be the same as indicated on the element body. If there is no voltage, then the part is broken or shorted. If the voltage is less than the optimal value, the element has lost part of its capacity.

Without desoldering, you can determine the faulty element visually. The capacitor may simply burst, have damage on the housing, carbon deposits or swelling.

Capacity test

A change in the capacitance of capacitors is easy to detect when measuring it with a multimeter that has this measurement mode.

The measurement occurs as follows:

1. Measuring probes are connected to the connectors for measuring capacitance (symbol Cx) observing their (probes) polarity. It is mandatory to completely discharge the capacitor before measuring this parameter.
2. Then , the working surfaces of the probes are connected to the terminals of the element being measured, also observing polarity in the case of taking readings from the polar type of the element being measured.
3. If the multimeter reading is equal to 0 or significantly different in value from those indicated on the capacitor, the latter is considered not working and requires replacement.

Visual inspection

Sometimes one glance is enough to identify a faulty capacitor on the board. In such cases, there is no point in checking it with any instruments. The capacitor must be replaced if a visual inspection shows the presence of:

• even slight swelling, traces of leaks;
• mechanical damage, dents;
• cracks, chips (relevant for ceramics).

Capacitors that have any of the above characteristics CANNOT be used.

Device with capacitance measurement function

In the settings panel of such models there is a “CX” sector. The measuring range is smaller than that of an LC meter (up to 200 µF), but it is sufficient for the most common elements.

The check is simple:

• the multimeter switch is set in the “CX” sector to the position with a numerical value that is closest to the expected capacitance;
• the capacitor leads are brought to the contact pads in the “CX” sector or they are touched with probes inserted into sockets with the same mark (depending on the model);
• The display will show the capacity.

Test results

Electrolytic capacitors are polarity sensitive. "CX" sockets and pads are marked with "+" and "-" symbols. The negative terminal of the capacitor is indicated by a tick.

Devices without capacitance measurement function

Such models are used in ohmmeter mode.

Procedure:

• the black probe is plugged into the “COM” socket (negative potential), the red one into the “V/Ω” socket (positive potential);
• the switch is set in the “Ω” sector to the 2 MOhm position;
• Observing polarity, touch the terminals with the probes.

In ohmmeter mode, the multimeter supplies voltage to the probes. It charges the capacitor and the resistance of the latter, gradually increasing from minuscule to a value of over 2 MOhm or infinity (indicated by one on the display).

The increase in resistance is most objectively reflected by an analog (arrow) tester. A malfunction is indicated by the behavior of the device when the resistance:

• immediately became infinite: the conclusion was cut off;
• stopped at below 2 MOhm: the capacitor is broken.

Based on the time during which the resistance increases from minimum to maximum, by comparison with known-good capacitors, you can approximately determine the capacitance of the test item.

This method is not suitable for testing capacitors with low capacitance - 20 µF and below. They charge quickly and even with a working element, the resistance almost immediately becomes infinite.

To test for reversible breakdown, the capacitor is connected to a laboratory DC source with a voltage regulator, and a multimeter in ammeter mode is connected in series with it. The voltage is gradually increased to the maximum permissible. If during this process the tester displays a non-zero current strength, then a reversible breakdown has occurred.

Practical measurements

The capacitance value of the capacitor is indicated on the case in fractional farads or using a color code. But over time, components can lose their qualities, so for some critical cases the consequences may be unacceptable. There are other circumstances that require measurements. For example, the need to know the total capacity of a circuit or piece of electrical equipment. There are no devices that directly read the capacitance, but the value can be calculated manually or by processors integrated into the measuring devices.

To detect the actual capacitance, an oscilloscope is often used as a means of measuring the time constant (t). This value indicates the time in seconds during which the capacitor is charged by 63%, and is equal to the product of the circuit resistance in ohms and the circuit capacitance in farads: t = RC. An oscilloscope makes it easy to determine the time constant and makes it possible to use calculations to find the required capacitance.

There are also many models of amateur and professional electronic measuring equipment equipped with functions for testing capacitors. Many digital multimeters have the ability to determine capacitance. These devices are capable of charging and discharging a capacitor in a controlled manner with a known current and, by analyzing the increase in the resulting voltage, produce a fairly accurate result. The only drawback of most of these devices is the relatively narrow range of measured values.

You might be interested in this: Digital multimeter and multitester measurement

Capacitor capacity

Determination of capacitor operating voltage

Strictly speaking, if there is no marking on the capacitor and the circuit in which it was installed is not known, then it is IMPOSSIBLE to find out its operating voltage using non-destructive methods.

However, having some experience, you can very roughly estimate the operating voltage based on the dimensions of the capacitor. Naturally, the larger the size of the capacitor and the smaller its capacity, the higher the voltage it is designed for.

Method No. 1: determining operating voltage through breakdown voltage

If there are several identical capacitors and you don’t mind sacrificing one of them, then you can determine the breakdown voltage, which is usually 2-3 times higher than the operating voltage.

The breakdown voltage of a capacitor is measured as follows. The capacitor is connected through a current-limiting resistor to an adjustable voltage source capable of delivering obviously more than the breakdown voltage. The voltage across the capacitor is controlled by a voltmeter.

Then the voltage is gradually increased until breakdown occurs (the moment when the voltage across the capacitor suddenly drops to zero). The operating voltage can be taken to be 2-3 times less than the breakdown voltage. But this is... You can have your own opinion on this matter.

Attention! Be sure to follow all safety precautions! When checking a capacitor for breakdown, it is necessary to use a protected stand, as well as personal eye protection.

The energy of a charged capacitor is enough to cause a small nuclear explosion right on your desktop. And some types of ceramic capacitors, during an electrical breakdown, can shatter into very small but hard fragments that can easily pierce the skin (not to mention the eyes).

Method No. 2: finding the operating voltage of the capacitor through the leakage current

This method of finding out the operating voltage of a capacitor is suitable for aluminum electrolytic capacitors (polar and non-polar). And the majority of such capacitors.

The point is to catch the moment at which its leakage current begins to increase nonlinearly. To do this, we assemble a simple circuit and measure the leakage current at various values ​​of the applied voltage (from 5 volts onwards). The voltage should be increased gradually, in equal portions, recording the readings of the voltmeter and microammeter in the table.

I ended up with a sign like this (my instincts told me that this was a fairly high-voltage capacitor, so I immediately started adding 10V at a time):

As soon as it becomes noticeable that the same increase in voltage each time leads to a disproportionately larger increase in the leakage current, the experiment should be stopped, since we are not faced with the task of bringing the capacitor to an electrical breakdown.

If you build a graph from the obtained values, it will look like this: It can be seen that starting from 50-60 volts, the graph of the leakage current versus voltage acquires a pronounced nonlinearity. And if we take into account the standard range of voltages:

Standard range of rated operating voltages of capacitors, V

We can assume that for a given capacitor the operating voltage is either 50 or 63 V. I agree, the method is quite labor-intensive, but not mentioning it would be a mistake.

The principle of operation of a capacitor: its charge and discharge

Capacitor charge.

When connected to a DC source, a charging current begins to flow through the capacitor. It decreases as the capacitor charges and eventually drops to the value of the self-discharge current, which is determined by the conductivity of the dielectric material.

The voltage across the capacitor smoothly increases from zero to the voltage of the power source.

When charging a capacitor, the current and voltage change exponentially. The charging time can be determined by the formula:

If we substitute resistance in the formula in Ohms, and in capacitance in Farads, we get the time in seconds during which the voltage on the capacitor changes e ≈ 2.72 times. A capacitor with a larger capacity will take longer to discharge, and will discharge faster to a lower resistance value.

Capacitor discharge.

If you connect a load resistance to a charged capacitor, the current through it will initially be maximum, then gradually drop to zero. The voltage on its plates will also change exponentially.

• 
  Why do you need a capacitor?

How to measure capacitor leakage current?

The method for measuring leakage current has already been described a little higher. I would just like to add that Iut is measured either at the maximum operating voltage of the capacitor or at the voltage at which the capacitor is planned to be used.

You can also calculate the leakage current of a capacitor by an indirect method - through the voltage drop across a previously known resistance. When checking polarized capacitors for leakage, it is necessary to observe the polarity of their connection. Otherwise, incorrect results will be obtained.

When measuring the leakage current of electrolytic capacitors after applying voltage, it is very important to wait some time (5-10 minutes) so that all electrochemical processes are completed. This is especially true for capacitors that have been out of service for a long time.

Electrolytic capacitors are tested for leakage using the trickle charging method as follows:

Prepare an ampere-volt-ohmmeter (for example, a combined device of type Ts435) to measure resistance on the “ R x X 100 ” scale. Then connect the ohmmeter conductors to the capacitor and wait until the instrument needle is positioned above one of the extreme marks on the left side of the scale. After this, disconnect one of the device’s conductors from the capacitor for a few seconds and, reconnecting it to the capacitor, notice the arrow jumping to the right. The greater the angle by which the needle deviates when recharging the capacitor, the greater the leakage current.

Inspection Precautions

Discharging the capacitor is mandatory. This is especially true for high-voltage parts - they can damage the multimeter or shock a person. Discharge by touching the legs with a metal object or connecting a lamp. The second method makes the discharge process smoother.

During measurement, do not touch the open parts of the probe with your hands - the human body has low resistance and a high leakage rate. In this case, the measurement will be incorrect. The current will follow the path of least resistance and the readings will show a value that has nothing to do with the capacitor.

Measurements on high-voltage capacitors are carried out using rubber gloves and insulated instruments.

A properly functioning electronic component is capable of storing and releasing a certain amount of electricity. Breakdowns during operation are determined not only visually, but also using a multimeter. Testing with a measuring device can clarify the suitability of an element for further use.

Potential energy of a charge in a uniform field

Since the field of a charged capacitor is uniform, it is easy to find the work done by moving charges in this field. A test charge $q$ placed in a field of intensity $E$ is acted upon by the force:

$$\overrightarrow F=q\overrightarrow E$$

This means that work will be done on the path $S$ lying along the field line:

$$A=qES$$

Since electric forces are conservative, it is important that the starting and ending points of charge movement lie on the same line of force; the trajectory of the path does not play a role. All work done is equal to the difference in potential energies at the starting and ending points

Rice. 2. Conservative forces in physics.

Taking the potential energy at the initial point to be zero, we find that the potential energy is equal to the perfect work of moving a charge along a line of force of a uniform electric field:

$$W=qES$$

Basic capacitor malfunctions

Capacitive elements play a large role in the circuit diagram of any device. Their main function is to charge a certain amount of current and pulse discharge into the circuit. The main malfunctions of capacitors include:

1. Normal breakdown. A breakdown can be caused by an increase in operating voltage. Repair requires not only replacing the element, but also determining the cause of the high voltage.
2. Internal break. If a radio component breaks, it loses its capacity, since both of its outputs become isolated. A break can occur when the device is dropped or the element itself is poorly assembled.
3. A leak. This problem is due to the loss of some capacity. The smaller the permissible and optimal capacity, the smaller the charge size.

What does capacity depend on?

Capacitance is the property of accumulating and retaining electrical charge. The larger it is, the greater the charge, which increases the capacity of the vessel with the gas cylinder. It depends on the shape and size of the electrodes. It also depends on the location and property of the dielectric separating the electrode. There are flat capacitor source with parallel and cylindrical plate.

It has not only a specially designed device, but also several conductors that are separated by a dielectric. Capacitance has a significant impact on AC electrical installations. For example, a source with a certain capacitance has an electrical wire with a live electrical cable, a conductor and a metal cable sheath.

What does capacity depend on?