Rheostats and Their Types

A rheostat is a type of variable resistor that is used to control current and vary the resistance in a circuit with no interruptions. They are built similarly to potentiometers, but rheostats use two connections, regardless of whether there are more than two terminals present or not, unlike a potentiometer. The first connection is at the end of the resistive element and the second connection is attached to the wiper which is a sliding contact. Rheostats always carry a substantial current; therefore, they are built to be wirewound resistors which consist of resistive wires wrapped around an insulating ceramic center and a wiper that slides over the windings.

Of the two connection points of a rheostat, one is moving, and the other is stationary. Sometimes, a rheostat may even have three connection points. These wirewound resistors, which are able to bear large currents, are typically built from nichrome wire that is surrounding a ceramic core. This core insulates heat energy and does not allow energy to flow through the rheostat.

Oftentimes in the past, rheostats were used as power control devices that directed features such as light intensity, motor speed, heating, and oven functionality. They are not used in this fashion anymore because of their inefficiency, relative to other devices now available like electrical switches. Rheostats are still used for tuning and calibration in circuits, and they will only be adjusted during fabrication and circuit tuning.

There exists many different types of rheostats, including rotary types which are often used in power control applications. The majority of rheostats are openly constructed, but enclosed varieties are also available. Multi-gang types are available to help control numerous applications or to create more power in a system. Moreover, rheostats feature a mechanical stop in order to reduce minimum and maximum resistances. Printed circuit boards often feature trimmers which are used to supply variable resistance. The most common resistor is the 3-terminal potentiometer which can be wired as a rheostat.

In order to wire a 3-terminal potentiometer into a rheostat, it must be connected to one end of the resistive track and wiper. Ideally, the wiper is connected to the other end of the resistor track which prevents the circuit from being interrupted if the wiper was to lose connection with the resistive track. Additionally, this also lessens noise. An example of a common potentiometer is a resistor with two fixed terminals and a third terminal that is connected to a contact arm. These are found in volume control equipment.

Rheostats are used in instances when electricity needs to be transmitted with high voltages, and they perform as either a variable resistor or a potential divider. Dimmers are an example of rheostats acting as a variable resistor to control the speed and intensity of light or fan rotations.

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