What Is a Rheostat?
1 min read
Quick answer
A rheostat is a two-terminal adjustable resistor used to adjust the current in a circuit. It's actually a potentiometer used with two of its terminals (the middle + one end).
How Does It Work?
As the wiper moves, the amount of resistance in the circuit changes; as resistance rises, the current falls by Ohm's law. So a rheostat adjusts the current directly.
Difference From a Potentiometer
| Property | Potentiometer | Rheostat |
|---|---|---|
| Terminals | 3 (voltage divider) | 2 (current adjustment) |
| What it adjusts | Voltage | Current |
| Power | Usually low | Usually high |
Where Is It Used?
In high-power adjustments such as motor speed control, lamp brightness (old style), heater control and current limiting.
Power and Cooling
Since the entire load current flows through the rheostat, it's usually built like a power resistor and heats up significantly. So it's made large with an open body and used, where possible, in environments with airflow.
Common Mistakes
- Exceeding the power rating: since the current through a rheostat is high, power-resistor properties are needed.
- Using it like a pot: where a three-terminal connection is required, a rheostat isn't enough.
- Forgetting cooling: it heats up significantly at high current.
Frequently Asked Questions
Rheostat or potentiometer?+
If you want to adjust current, a rheostat (2 terminals); if you want to divide voltage, a potentiometer (3 terminals).
Can I use a potentiometer as a rheostat?+
Yes; if you use the middle terminal and one end, a potentiometer behaves like a rheostat.
Search parts related to "What Is a Rheostat?"
Find the right part by comparing price, stock and distributors.