Capacitors

A capacitor is a component that stores an electrical charge. It consists of two plates separated by an insulator. The amount of capacitance is measured in Farads but as this is too large a unit for everyday electronics we use smaller units such as microfarads and smaller. Capacitors come in many types including electrolytic, polyster, polypropylene, ceramic, paper and mica.

Measurement and Testing

The best check of a capacitor is to use a meter designed to perform the necessary tests. However, an ohmmeter can identify those in which the dielectric has deteriorated (especially in paper and electrolytic capacitors). As the dielectric breaks down, the insulating qualities decrease to a point where the resistance between the plates drops to a relatively low level. After ensuring that the capacitor is fully discharged, place an ohmmeter across the capacitor, as shown in figure. In a polarized capacitor, the polarities of the meter should match those of the capacitor. A low-resistance reading (zero ohms to a few hundred ohms) normally indicates a defective capacitor.