Question

What symbol would best represent an electric fan speed controller in an electric circuit?

Answer 1

There is no single universal schematic symbol specifically labeled “fan speed controller.” Which symbol to use depends on how the controller works and how detailed you want the diagram to be. Common choices:

- Simple/manual control (most common in simple schematics)
- Use a variable resistor (rheostat / potentiometer) symbol drawn in series with the motor. Label it POT or RV (e.g. RV1). This clearly indicates adjustable series resistance to change motor torque/speed.
- How to draw: a resistor symbol with an arrow touching it (or a resistor with a diagonal arrow).

- Solid‑state (phase‑angle) controller for AC fans
- Use a TRIAC symbol (or SCR pair) in series with the motor, optionally with a small control network shown or a knob symbol and label “phase controller.” Or draw a box labeled “triac speed controller” if you don’t want circuit details.

- PWM/DC controllers
- Use a transistor/MOSFET symbol in series with the motor (or a box labeled “PWM controller”) and annotate “PWM” or “DC speed control.”

- Block/functional diagrams
- Draw a simple rectangle labelled “Fan speed controller” with input/output wires and a small knob icon. This is best when you don’t need internal circuitry shown.

So: for most schematic purposes where you just want to show an adjustable control, use the variable resistor symbol in series with the fan; for more realistic/accurate representations use the appropriate semiconductor symbol (triac/MOSFET) or a labeled box.