Paper capacitors are one of the basic types of capacitors. Typically, in capacitor formation, conductive materials are separated by dielectrics, and different types of capacitors are based on variations of the dielectric. The construction of this capacitor is similar to other capacitors, such as plastic capacitors. The only difference between other capacitors and this capacitor is that the dielectric chosen is paper. Paper capacitors are called fixed capacitors where paper is used as a dielectric and it stores energy in the form of support.
This type of capacitor is used in capacitance values of 1nF to 1uF at power line frequencies and it stores a fixed amount of capacitor. These capacitors tend to store a fixed number of capacitors, so these capacitors are listed as fixed types of capacitors. To compensate or protect dielectric workstations from environmental influences, immerse them in wax or oil.
Ⅰ.Paper capacitance value
The capacitance of paper capacitors is measured in farads. The capacitance of this capacitor ranges from 0.001 to 2.000 microfarads to the high voltage range of 2000V. In the beginning of this capacitor, paper was used as the dielectric between two aluminum sheets but now other materials like plastic are used instead of paper. This capacitor is readily available in the 300 picofarad to 4 microfarad range and operates at 600 volts.
Ⅱ. Working principle of paper capacitor
Paper capacitors consist of two metal plates with paper used as the dielectric material between them. There are positive and negative plates in it and when a charge is applied to the plate, the positive plate is attracted to one side and the negative charge is attracted to the other plate. This electrical energy is stored in the form of an electric field, and this collected electrical energy is used by discharging the capacitor. These range from 500pF to 50nF. This results in high leakage current.
Image: Working principle diagram of paper capacitor
Ⅲ.Structure of paper capacitor
There are two types of paper capacitors: paper capacitors and metallized paper capacitors.
3.1 Paper Capacitor
The construction of this capacitor requires two sheets of aluminum and a piece of paper, which is completely covered with wax to protect it from the elements in the open air. A paper capacitor is a fixed capacitor that stores a fixed amount of charge at a fixed value of charge capacitance, with aluminum plates placed between sheets of paper that act as dielectrics, while the aluminum acts as electrodes.
Image: Paper capacitor with paper pieces
Paper is a very poor conductor of electricity and does not allow electricity to pass between the aluminum sheets. Allows electric fields to pass through it, acting as a barrier to electrical current. The paper and aluminum sheets are rotated into a cylinder shape, and the entire cylinder is coated with wax or plastic resin to protect it from the humidity of the outside air, and two wires are led from the ends of the two aluminum sheets.
3.2 Metallized paper capacitors
In this paper capacitor, the paper is coated with a thin layer of zinc or aluminum and rotated in the form of a cylinder. The entire cylinder is completely coated with wax to protect it from dust and moisture in the external environment, with metal paper electrodes and paper acting as dielectrics.
Image: Metallized paper capacitor
Such zinc-coated capacitors are easily damaged due to chemical effects, which is why aluminum is widely used in the manufacture of such capacitors. Compared with paper capacitors and metal paper capacitors, metal paper capacitors are smaller in size. This is because it has a very thin layer of aluminum compared to the aluminum wrapped in a paper capacitor.
Ⅳ. Advantages and Disadvantages of Paper Capacitors
The main advantage of using paper capacitors is that it provides a fixed capacitance value. And the capacitance value during their production can be determined; the main disadvantage of paper capacitors is that they absorb moisture from the atmosphere and reduce the insulation resistance of the dielectric. The dielectric affects it because it absorbs moisture from the atmosphere.
Ⅴ. Application of paper capacitors
In electrical and electronic circuits
In high voltage and high current applications
Used as a sensor to measure air humidity, fuel level and mechanical stress
Car audio systems are used to add extra power to amplifiers as needed
Used in electronic noise filtering, signal coupling and decoupling systems, remote sensing
Blocks DC signals in power conditioning systems and allows AC signals to pass through
Used in signal processing systems such as speakers, dynamic random access memory (DRAM), tuning circuits, radio receivers and analog equalizers
Ⅵ. Issues related to paper capacitors
6.1 Is paper the dielectric in capacitors?
Paper capacitors are also called fixed capacitors, where paper acts as a dielectric to store energy in the form of an electric field.
6.2 Is paper a good dielectric?
Yes, paper’s cellulose fiber matrix has excellent dielectric properties. Paper was a very popular dielectric medium during the last century. Before the advent of modern, defect-free polymer films, “paper capacitors” were widely used in early electrical, electronic and radio equipment.
6.3 What are paper capacitors used for?
Paper capacitors are used in electronic noise filtering, signal coupling and decoupling systems, and remote sensing systems. Used in signal processing systems such as tuners, speakers, dynamic random access memories (DRAM), radio receivers and analog equalizers, it is useful in screening applications.
6.4 Do paper capacitors have polarity?
Paper capacitors are not polarized. But the body of the capacitor is usually marked with a ribbon on one end. The strip indicates the terminal connected to the outermost plate of the capacitor.
6.5 How are paper capacitors made?
The construction of this paper capacitor requires two aluminum sheets and a piece of paper. The paper acts as a dielectric between the aluminum plates, the aluminum sheets act as electrodes, and the paper acts as a barrier to the electrical current between the aluminum plates.
The above is an introduction to paper capacitors. If you want to determine the quality of a capacitor, all you need is a wide range digital multimeter and any type of capacitor in your device. Connect the multimeter leads to both ends of the capacitor plate. Connect the red lead of the multimeter to the positive plate of the capacitor and the black lead to the negative plate.If the meter reading starts at zero and gradually increases to infinity, the capacitor is good. Therefore, a capacitor can be checked with a digital and analog multimeter to determine if it is good, bad, open, or short.