Electrolytic capacitor: the main parameters of the device, how it works and what determines the large capacity

An electrolytic capacitor is present in the designs of the vast majority of electrical appliances. Televisions, radio, audio equipment, washing machines, air conditioners, computers, printers - this is not a complete list of devices equipped with such a capacitor. The device is widely used not only in household devices used in everyday life, but also in the industrial, military and construction sectors.

Design features

The wide range of applications for electrolytic capacitors is due to their high functional properties and simplicity of design. With a relatively small size, they have a fairly large capacity. The aluminum standard condenser system consists of:

1. Two paper tapes. For their manufacture, a special capacitor paper is used, impregnated with a compound that conducts an electric current.
2. Two aluminum strips. Foil for their production is processed in a special way.

All strips are rolled into a single roll. The role of the active element is played by the leads connected to the electrodes and equipped with a seal. The entire structure is enclosed in a cylinder-shaped aluminum body.

Several types of models are produced on the basis of this system:

• with leads located in one direction;
• with increased mechanical strength of fastening;
• for surface mounting.

Production stages

All high-capacity electrolytic capacitors are manufactured using proven technology. The production process consists of several important stages:

1. Foil etching. This term is usually used to denote the procedure for increasing the effective surface area. The increase in area becomes possible due to electrochemical corrosion or chemical erosion. The pulsating current, together with a certain temperature and composition of the electrolyte, changes the shape, size of the foil and the number of microscopic channels on its surface.
2. Oxide layer formation. Anode foil that has undergone the etching procedure undergoes oxidation, i.e. it is exposed to a solution of ammonium salts, phosphoric or boric acid (in the case of high-voltage capacitors). In some cases, a layer of aluminum oxide Al2O3 is also grown on the cathode foil.
3. Slicing. Strips of a given length and width are cut from paper and foil that has undergone the necessary processing.
4. Connection of leads. They are connected to the electrodes using cold or spot welding.
5. Impregnation. It is produced in order to fill the pores of capacitor paper with electrolyte. Before this, the electrolytic capacitor is dehumidified under pressure. The pores must contain a certain volume of electrolyte. Its excess is removed by placing the elements in a centrifuge. To avoid the loss of electrolyte, rubber seals are installed inside the device.

The final stage of production is the assembly of all parts into a single device, covered with a protective aluminum housing and an insulating shell. Another mandatory step is to check for damage to the oxide layer and restore it.

Main characteristics

The capacitor design is most easily presented in a simplified description. On it you can see the main parameters of electrolytic capacitors:

1. Capacity. This indicator is in direct proportion to the temperature. A drop in temperature (to zero and below) leads to the fact that the viscosity of the electrolyte composition (as well as the resistance in the microscopic pores of the foil) increases, leading to a decrease in volume. An increase in temperature above 20 degrees, on the contrary, leads to the expansion of parts and the total capacity of the device. Also, the value of this indicator depends on the frequency. The frequency and amplitude of the alternating voltage applied to the device help determine its capacity.
2. Equivalent Series Resistance (ESR). Its size and relationship with other quantities is determined by the formula ESR = (tan δ) / (2 * π * f * ESС). The angle δ is formed between the voltage vector of a particular capacitor and the voltage vector at the ideal capacitance. Tan δ is the quotient of active power divided by reactive power (when the voltage is sinusoidal).
3. Total resistance (impedance) is obtained as a result of the total action of the capacitance of the oxide layer, active resistance paper separator and electrolyte, capacity of the separator impregnated with electrolyte, inductance of windings and terminals capacitor.

Another important characteristic is the rate of current passed through the dielectric oxide layer on the positive electrode. If the capacitor has not received voltage for a long time, the leakage current will be high. This indicates the destruction of the aluminum oxide layer.

Varieties of capacitors

An integral part of the device and the key to its effective operation is the presence of electrolyte between the plates. Depending on which composition performs this function, capacitors are:

• dry;
• liquid;
• oxide metal;
• oxide semiconductor.

A distinctive feature of oxide-semiconductor devices is that the role of the cathode in them is played by a semiconductor deposited directly on aluminum oxide. The anode can be made from aluminum, tantalum, niobium or sintered powder.

The presence of a cathode and anode indicates that the electrolytic capacitor belongs to the category of polar devices. Its operation is possible with the passage of current only in one direction. Non-polar electrolytes have been developed to work in electrical circuits with sinusoidal currents. During their production, additional elements are used that significantly increase the size and price of finished devices.

A separate type of device that ensures the flow of electrochemical processes is an ionistor. Its principle of operation is based on the contact of the electrolyte with the plate, as a result of which a double electric layer is formed. This design allows the supercapacitor to be used not only for its intended purpose, but also as a chemical source of electricity.

The capacitance of the supercapacitor collected in a short time can be maintained for a long time. At a voltage of about ten volts, the capacitance can reach several farads. With an optimally selected combination of voltage and temperature, its working life can reach 40 thousand hours. However, the fluctuation of the initially set characteristics will provoke a decrease in the service life by several tens of times (up to 500 hours).

The area of ​​application of supercapacitors is wide. They are used to back up different power supplies. They are successfully used in solar panels, car radio equipment and smart homes.