The two primary ways to control the speed of a single-phase AC motor is to either change the frequency of the line voltage the motor sees or by changing the voltage seen by the motor, thereby changing the rotational speed of the motor.

Current flows from the negative terminal of the battery, through the circuit, and to the positive terminal of the battery.

AC motors are constant speed devices but their speed can vary if you change the input voltage or frequency or the windings that make the motor rotate. The most common and efficient way of changing the speed is to vary the frequency by using an inverter as the power supply.

No you can’t use a dimmer switch to control a DC motor. A dimmer uses diac and triac and only works with AC which commutates the triac OFF at the end of every half cycle. Also keep in mind universal motors don’t speed control very well anyway and need to have a viscous load to enable speed controlling to happen.

No. Some motors cannot change their speed at all – steppers, induction motors and synchronous motors. Some motors require different speed control techniques – brushless DC, and many others. DC motors can vary speed by changing the armature or field voltage.

If you mean that you want to control the speed of an AC fan with a potentiometer, it is probably not possible. Whether an AC “mains” fan can be speed controlled with a pot depends on the technology used. Single phase induction motor – capacitor start usually.

Slowing down a single phase AC motor can be complicated and expensive. They are usually built to be run at a certain speed and anything else would be tricking it to do something it wasn’t meant to. Simply slowing it down may cause it to overheat with reduced mechanical self-cooling.

The firing angle of a thyristor like TRIAC – that gives supply to motor, is delayed to decrease the motor speed or it is fired earlier to increase motor speed. As firing angle is changed, the part of AC waveform applied to motor is chopped more or less.

AC Fan Speed Control using Arduino and TRIAC

1. Components Required.
2. Working of AC fan control using Arduino.
3. Zero-Crossing Detector.
4. Phase Angle controlling Circuit.
5. Potentiometer to control the Fan Speed.
6. PWM Signal Generation Unit.
7. Circuit Diagram.
8. Programming the Arduino for AC fan speed control.

You can use arduino UNO with a solid state relay SSR. Use pwm pulses to control the SSR. This will automatically control the on and off switching and speed of the AC motor.

The project controls the AC voltage by sending pulses to the Gate pin of BT136 TRIAC. When the circuit is powered ON, the Arduino sketch initializes the circuit and start reading analog voltage supplied through variable resistance at A0 pin. The zero voltage crossing is detected by the 4N25 circuit.

Arduino Motor Control Setup

1. Connect 5V and ground of the IC to 5V and ground of Arduino.
2. Connect the motor to pins 2 and 3 of the IC.
3. Connect IN1 of the IC to pin 8 of Arduino.
4. Connect IN2 of the IC to pin 9 of Arduino.
5. Connect EN1 of IC to pin 2 of Arduino.
6. Connect SENS A pin of IC to the ground.

Plug the second motor into the terminal labelled OUT3 and OUT4: 2.) The row of pins on the bottom right of the L298N control the speed and direction of the motors. IN1 and IN2 control the direction of the motor connected to OUT1 and OUT2.