A capacitor is an electronic component that stores energy in the form of an electric field. Without delving too deeply into the physics of electricity, capacitors achieve an electric field by accumulating charge on two conductive plates at different voltages (as in Fig. 1). These conductive plates are separated by a special type of insulator called a dielectric. Different factors, like the properties of the dielectric, area of the plate, and the distance between the plates, affect how much energy can be stored. The amount of energy that can be stored is measured in Farads. Capacitors typically hold somewhere between a few picofarads (pF; one picofarad is 10-12 of a Farad) to hundreds of microfarads (µF one microfarad is 10-6 of a Farad). Large capacitors that hold tens of farads or more are referred to as “super-capacitors” or “ultra-capacitors”. They are not very common due to their impractical size. Using one would be comparable to building a car with 1000 gallon gas tank.
It is difficult to understand how a capacitor reacts in a circuit based by trying to theorize it. It is simpler to describe its properties using a water analogy. Capacitors work very similar to an elastic wall sealed in the middle of a pipe. When this hydraulic capacitor is placed between a pressure drop, the elastic divider will stretch and store the energy. The hydraulic capacitor analogy illustrates a few important properties of capacitors.
There are many different kinds of capacitors. This is because a wide variety of different materials can be used for the dielectric. Both electrolytic capacitors and ceramic capacitors are fairly common, so we will focus on them.
Electrolytic capacitors are the most common type of capacitor. Generally, they are cylindrical in shape and are used when the circuit calls for a large capacitance. Electrolytic capacitors have a polarity, so they must be connected correctly to avoid damage. The negative side of the capacitor is denoted by a white stripe. The capacity and maximum voltage values are also printed directly on the capacitor, as shown in Fig. 4.
Ceramic capacitors are much smaller than electrolytic capacitors. Generally, they are shaped like small disks and have no polarity. Their capacitance is printed as a code on the component. The code will either be two or three digits and may have a tolerance letter on the end (see Fig. 5).
All ceramic capacitor codes indicate the capacitor value in picofarads (pF). Two digit codes do not need to be decoded, as they simply specify what the capacitance is in pF. Three digit codes work the same way (the first two digits represent a number not a code), except the third digit represents the power by which you should multiply (see Fig. 6). Finally, a letter on the end of a three digit code designates the tolerance (also shown in Fig. 6). Capacitor tolerance is how much accepted error there is in the capacitance value due to the manufacturing process. Below are some examples of converting capacitor codes to their values.