Many people don’t know much about capacitors. Let’s share some relevant little knowledge today! Are you interested in the introduction of paper capacitors and electrolytic capacitors?
There are many kinds of paper capacitors, which are divided into the shape of the outer casing, such as vertical square, horizontal square, round and so on. According to the material of the outer casing, there are porcelain shells, iron shells, aluminum shells, and the like. From the sealing situation, there are sealed, semi-sealed and so on. From the pressure resistance, there are tens of volts to tens of thousands of volts. From the capacity, there are dozens of picofarads to 10 microfarads or more. From cold resistance, from minus 10 ° C to minus 60 ° C. From heat resistance, from 20 ° C to 100 ° C and so on. The commonly used paper capacitors for radios are unsealed, with voltages below 1000 volts, capacities below 0.5 microfarads, heat resistance from 40 ° C to 60 ° C, and errors from ± 10% to ± 20%. The structure of the paper capacitor is also relatively simple, mainly two layers of aluminum foil or tin foil, sandwiched between two or more layers (depending on the pressure) of capacitor paper, wound into a cylindrical capacitor core, with fire paint or asphalt Closed, labeled, ok.
There are two kinds of winding methods for paper capacitors. One is the non-inductive winding method, which has the advantage of reducing the distributed inductance. The other is the inductive winding method, which is also commonly used in radios due to the large distributed inductance. It is easy to cause interference, but it is simpler than non-inductive manufacturing. Therefore, inductive capacitors usually ground the leads of the outer aluminum foil to reduce interference. Only by selecting a good quality capacitor can the quality of the product be guaranteed. When choosing, first pay attention to the two lacquers or asphalt. There should be no pores, dents, softening, etc. Otherwise, it will easily absorb moisture and deteriorate or break open, short circuit, etc., causing the product to work abnormally or even silently. In addition, the capacitor leads should be free from scratches and shaking, otherwise they are easy to break, or loose because the leads are not firmly fixed, causing the radio to be intermittent. When selecting, you can use your hand to gently shake the lead, and there is no activity to use.
Let us introduce the electrolytic capacitor. There are many types of electrolytic capacitors, such as round aluminum shells, square iron shells, and paper shells. Sealed, semi-sealed and unsealed, etc. The characteristics of aluminum foil electrolytic capacitors are mainly large capacitance, generally from 1 to 20,000 microfarads or higher, but the voltage is low, the maximum is not more than 500 volts, and the lowest is about 6 volts. In addition, the error is large, generally more or less 20%, and the capacity is unstable, with a large change in temperature and time, large loss, and short life. In addition, not all electrolytic capacitors can be used in very cold and hot places, and some can only be used at minus 10 ° C or minus 20 ° C, positive 40 ° C, and some can be used at minus 40 ° C and minus 60 ° C. , to use at 60 ° C to 70 ° C, according to the different requirements of the machine, choose different electrolytic capacitors. The electrolytic capacitors used in general radios are 450 volts or 300 volts, 20 microfarads, 16 microfarads or 8 microfarads, unsealed aluminum or paper casings, and negative electrolytic capacitors from 20 ° C to plus 60 ° C.
The structure of the electrolytic capacitor for the radio is mainly to chemically treat the aluminum foil as an anode to obtain an oxide film as a medium, and to make an electric paste with a chemical material such as glycerin (or ethylene glycol), ammonia water or boric acid, and then apply it. On the burr paper, as a cathode. In order to make better contact, the outside of the cathode can be covered with a layer of aluminum foil of lower purity, rolled into a cylindrical shape, filled into a paper case, filled with lacquer or asphalt, and the trademark is a paper-shell electrolytic capacitor used in the radio. In the aluminum case, it is an aluminum shell semi-sealed electrolytic capacitor. The paper-shell electrolytic capacitors are generally marked with “+” and “-” on the label paper. When used, the “+” sign indicates that the positive electrode is connected, and the “-” sign indicates that the grounding or the negative electrode is connected, and the fault cannot be connected, otherwise it will break down.
If the negative electrode is to be eliminated, it is necessary to form an oxide film on the cathode aluminum foil and the anode aluminum foil to avoid it. But this is not only a complicated process, but also a small capacity. For example, in the radio, the paper-shell electrolytic capacitor is mainly used in a rectifying part and a resistor, and the pulsating DC current obtained after rectification is smoother. If the quality is not good, aging will cause the radio to make a “squeaky” hum. If the withstand voltage is not enough, it will be broken down or short-circuited, which will make the rectifier load too high, and generate high heat, burn out the coil of the rectifier or power transformer, and have no high-voltage output, making the radio silent. Therefore, the quality of electrolytic capacitors is very important and should be carefully selected. When using, it is best to measure the capacitance with an electric meter. The resistance of the electrolytic capacitor can be measured by the ohmmeter of the three-meter meter to judge the loss or short circuit to ensure the normal operation of the radio.
Do you know about the introduction of paper capacitors and electrolytic capacitors?
Post time: Dec-17-2018