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How To Discharge A Capacitor Safely?

How To Discharge A Capacitor Safely?

December 13 , 2023 0

Why discharge the capacitor. In the installation of electronic components, if the charged capacitor is broken, it will burn the electronic components in the circuit, and there is a risk of electric shock and fire. The larger the capacitance and voltage of the capacitor, the greater the degree of damage in the case of short circuit. This article will explain how to discharge the capacitor

How Do Capacitors Work?

A capacitor is a system in which two electrodes are separated by a dielectric in which an equal amount of charge of opposite potential is gathered. There are many types of capacitors, which can be divided into several sub-types. The simplest type of these are made of two metal plates with a dielectric between them - such as air, ceramic material, or impregnated paper. These plates are capacitor plates used to store electrical energy.

Applying a voltage to the capacitor plate starts to generate an electric charge - this is similar to a battery cell. After the voltage source is disconnected, the charge remains on the capacitor plate due to electrostatic attraction. The accumulated charges are equal but the potentials are opposite.

The safe discharge of a capacitor is similar to its charging process. After a DC voltage U characterized by a specific capacitance is applied to the capacitor terminal, charge Q accumulates in the capacitor, which is the product of capacitance and voltage. The unit of capacitance of a capacitor is farad. In a 1-farad capacitor, 1 coulomb of charge produces 1 volt. Since 1 farad is a very large value, capacitors used for electronic power typically have capacities in the order of picofarad, nanofarad, microfa, and millifa.

Solid capacitors are divided into two basic categories: film capacitors and ceramic capacitors. The safe discharge of a capacitor depends largely on its design. Polystyrene capacitors are characterized by high stability and insulation resistivity, as well as a fairly low upper operating temperature limit.

Thin film capacitors are made of three thin films, respectively electrode - dielectric - electrode, which are then rolled up and placed in a suitable housing. They are often used in electrical and electronic systems for various household appliances and electronic products.

Capacitor Parameter

In order to know how to discharge a capacitor, it is necessary to know the parameters that characterize the electrical component. The basic parameters of capacitors are: rated capacitance, capacitance tolerance, rated voltage and dielectric loss.

In addition, the characteristics of the capacitor are: the allowable AC voltage, insulation resistance, capacitance temperature coefficient, climate class and size, as well as the allowable pulse load, rated power and limit frequency.

Capacitance is the most important parameter to consider when planning the safe discharge of a capacitor. This is the ability of the capacitor to accumulate charge, which is proportional to the product of the dielectric constant and the area of the electrode plate, and inversely proportional to the distance between the electrodes (dielectric thickness).

The capacitance of the capacitor given by the manufacturer is rated capacitance, which is practically impossible to achieve, and the capacitance value can be affected by many environmental factors. Therefore, the percentage tolerance of the capacitor capacitance given is the percentage deviation of the actual value of the capacitor from the nominal value.

Capacitor loss determines the unit energy loss associated with capacitor operation at AC voltage, which is characterized by the tangent of the loss Angle. These losses are usually greater than dielectric losses, which are related to the occurrence of losses on the electrodes and the frequency and temperature that affect the capacitor system.

How To Discharge A Capacitor?

The discharge of a capacitor depends on its type and capacity. Capacitors with larger capacitors should be discharged more carefully, because a short circuit may not only damage the capacitor, but also cause an explosion and electric shock.

The safe discharge of a capacitor consists in connecting any resistive load at its ends to its ends, which will be able to dissipate the electrical energy stored in the capacitor. For example: How to discharge a 100 V capacitor? For this purpose, an ordinary resistor or a lamp with a voltage of 110 V can be used, the capacitor illuminates the lamp by providing electrical energy, and the light source can also indicate the charging state of the component. Of course, another resistive receiver may also be used for this purpose.

The discharge of capacitors should be carried out using a high resistance receiver. In this way, the release of the charge accumulated on the plate will take longer, but this will ensure that the charge is fully released.

It is also possible to discharge a capacitor with a smaller capacitance by preparing a special discharge circuit, which consists of a capacitor and a resistor connected in series. When preparing such a discharge system, note the discharge time of the capacitor and the amount of resistor power required.

The capacitor discharge time will be equal to the product of the resistance value and capacitance in series with the capacitor. After this time, the voltage of the element should drop to one-third of the initial voltage, and the charge should be fully released in five times the time of the product of resistance and capacitance.

The smaller the resistance we plug into the system, the faster the capacitor will discharge. For example, if a 10 uF capacitor is discharged with a 1kΩ resistor, the discharge time will be 0.01 s. If such resistance is used to discharge a capacitor of 1 mF, the discharge time of 1/3 of the initial charge value is extended to 1 s.

It should be remembered that the safe discharge of capacitors must be carried out with the appropriate resistance. Resistors with too little power will be damaged. Therefore, when selecting a resistor, the power consumption of the resistor should be considered, which is equal to the square of its voltage divided by the resistance. Standard resistors can carry up to 0.25W of power. Using this resistor with a large capacitor with a large charge and voltage will cause it to burn out. Therefore, in the case of smaller components, it is worthwhile to use resistors of 5W and, for example, 1 kω, of which the SR PASSIVES MOF5WS-1K model is an example.

Larger capacitors should be equipped with discharge resistors that discharge the element within a few minutes after disconnecting the supply voltage. A YDY 4mm2 cable should be used for safe discharge of the three-phase power capacitor, including shorting the phases of the component with a PE conductor.