Capacitors are components that store an electric charge. Conductors allow electricity to flow easily, while non-conductors do not. Capacitors are formed by placing a non-conductor, such as air, between two conductors, such as those made of copper. Capacitor strength is measured in units called farads. This is a large unit, and so typical devices are built using percentages, such as one-millionth of a farad.
Capacitors are categorised according to their materials, shapes and sizes. The materials include ceramics and plastic films. Electrolytic capacitors are made using oxide films placed onto metal. To read capacitor values printed on parts, learn to recognise the types and read the labels printed on them. These labels usually indicate the amount of capacitance and size of the voltage the device can handle safely.
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Things you need
- Electrolytic capacitor
- Disk capacitor
- Plastic film capacitor
- An introductory electronics textbook
Identify the units commonly used in capacitance. They are microfarads, nanofarads and picofarads. A microfarad is 10^(-6) farads, a nanofarad is 10^(-9) farads and a picofarad is 10^(-12) farads.
Examine the abbreviations for the most common units. Microfarads may be represented using the Greek letter mu. They also are abbreviated as u, M, MF, or MFD. Picofarads may be represented using p or pf. Sometimes p is capitalised. Nanofarads may be represented using n or nf, where sometimes the n is capitalised. Volts are represented using V or VDC, where DC is direct current.
Practice reading the labels on electrolytic and plastic film capacitors. An electrolytic that has the lettering 25V 2200 uF(M) means that it has a capacitance of 2200 microfarads, and can operate safely at 25 volts. A tubular plastic film capacitor that has a label 0.1 MFD +/- 10% 80 VDC means that it has a capacitance of 0.1 microfarads, where the value may be off by as much as 10 per cent, a variation known as tolerance. The component can operate safely at 80 volts.
Study the symbols used on the orange ceramic disk capacitors sometimes referred to as pancakes. They may have three digits and a letter. They are measured in picofarads, where the third digit is the number of multipliers or zeros, and the letter indicates the tolerance. The tolerance must be looked up with the use of a chart.
Practice reading the label on a disk capacitor. The label 103M means that 10 is followed by a multiplier of 3 zeros, which means that the device has a capacitance of 10,000 picofarads. This is the same as 0.01 microfarads. M means that the tolerance is 20 per cent.
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