A rheostat adjusts electrical resistance mechanically, usually via a wiper sliding across a coiled resistive wire. Unlike a potentiometer which acts as a voltage divider using three terminals, a rheostat uses only two terminals to directly restrict current. They are traditionally used for high-power applications like dimming lights or controlling motor speeds, though they have largely been replaced by solid-state switching components.
The motor speed is drifting because the wiper on the rheostat has oxidized and is losing contact.
You can wire a standard three-terminal potentiometer as a rheostat by tying the wiper to one of the end terminals.
Do not mix it up with
- Potentiometer: A potentiometer has three terminals and divides voltage; a rheostat uses two terminals to limit current.
Related terms
Potentiometer
A three-terminal variable resistor used to manually adjust voltage or resistance in a circuit.
Resistor
A passive two-terminal component used to limit current flow, divide voltages, or terminate transmission lines.
Trimpot
A small, adjustable resistor used for fine-tuning a circuit during manufacturing or calibration.