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Industrial electricians must understand the series - capacitors

First, electrolytic capacitors why large capacity and small volume

The positive electrode of the electrolytic capacitor is corroded by the electrolyte, and its surface is very rough, but this greatly increases the effective area and capacitance, and the oxide film as a medium is very thin, which also increases the capacitance, so its capacity is large and its volume is small.

What are the indicators to measure the performance and standard of the capacitor

There are two main indicators:

(1) Nominal capacitance, simply speaking, is the capacitance on the capacitor shell, this capacitance refers to the standardized capacitance value, provided by the standard series. It has a certain allowable error with the actual capacitance. The allowable error is divided into five levels: ±1% (level 00), ±2% (level 0), ±5% (level I), ±10% (level II), ±20% (level III). The permissible error range for electrolytic capacitors is large, ranging from -20% to +100%

The actual capacitance of the capacitor can be measured with a multimeter.

Voltage resistance (rated voltage). Voltage resistance refers to the capacitor long-term work, electrode voltage is not allowed to exceed the specified value, in case of capacitor breakdown or not allowed heating. The voltage resistance is generally marked on the shell with DC voltage. For special AC capacitors, the EFFECTIVE value of AC is also marked, and the AC is indicated.

In addition, there are insulation resistance, dielectric loss and stability indicators. When selecting capacitors, capacitance and voltage resistance must meet the requirements, and then consider the requirements of other characteristics according to different needs. Such as cable system and high frequency circuit should be used in low dielectric loss capacitors, resonance circuit use mica capacitors and ceramic capacitors, isolation can choose paper, mica, polyester, electrolytic capacitors, used as a filter can choose electrolytic capacitors.

Three, how to check and judge the quality of the capacitor

Measuring starting capacitance:

1, judge the polarity, first the multimeter to 100 or 1K ohm, assume a very positive, let the black pen and it is connected, red pen and the other pole connection, write down the resistance, and then the capacitor discharge, that is, let the poles contact, and then change the pen resistance, resistance is a large black pen connected with the positive electrode of the capacitor.

2. Adjust the multimeter to the appropriate ohm gear. The principle of gear selection is: the capacitor of 1μF is 20K, the capacitor of 1-100μF is 2K, and the capacitor of greater than 100 is 200.

3, and then use the red pen of the multimeter to connect the positive pole of the capacitor, the black pen to connect the negative pole of the capacitor, if the display slowly increases from 0, and finally shows the overflow symbol 1, the capacitor is normal, if always displayed as 0, the capacitor internal short circuit, if always displayed 1, the capacitor internal disconnect.

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