How2Day: Different Kinds of Resistors

Resistors are used to restrict current flow. Maria Toutoudaki/Photodisc/Getty Images
Resistors are a component responsible for controlling the elements that flow through an electrical circuit. The amount of resistance used is determined by the desired results. A circuit for high current flow uses a low resistance value. Depending on the circuit design, resistors can be added to increase the resistance value or decrease resistance value.

Resistors divide into two major categories, fixed resistors and variable resistors. In electronic circuits, the are chosen according to their value. The value and the tolerance level of the resistor are indicated by a color code printed on the resistor. The value of the resistor is not adjustable. A resistor with a brown, black, red and gold band has a value of 102 ohms and a 5 percent tolerance. The tolerance level indicate the highest and lowest amount of resistance the resistor will have. At the highest level of resistance, the resistor will have 107 ohms of resistance. The lowest resistance level is 97 ohms of resistance.

A variable resistor varies with the need of the electrical circuit. Carbon composition, carbon film, metal oxide, and wire wound are the different types of variable resistors.

Carbon resistors are cheap, general purpose resistors. The resistor is manufactured from finely ground carbon dust or graphite. The material is held together by non-conducting ceramic powder. The resistive value is determined by the carbon-to-ceramic ratio. A higher ratio mean a lower resistance. The carbon and ceramic mixture is coated in an insulator. Metal wires are attached to both sides so that the resistor can be connected to an electric connection. The value of the resistor is marked by color coded bands.

Wire wound resistors are used in high power applications such as circuits with power over 300 watts. Ranging from 10 ohms to 100,000 ohms, they are best used in circuits with high current needs. Wire wound resistors are made by wrapping a resistance wire around a ceramic core.

To increase the surface area performance and decrease heat loss, the resistors are molded with an aluminum heat sink body.

Metal film, carbon film, and metal oxide are film resistor types. The resistors are made with either pure metals such as nickel or an oxide film like tin-oxide. The substance is deposited onto an insulating ceramic rod. The thickness of the film determines the resistance value. The tolerance of the resistance varies by 1 percent or less.

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