I have a fan which has asynchronous motor. It's features are that 230V AC, 50 Hz, 50W. I want to control it's speed using AC dimmer. I can control the brightness of light bulb with my dimmer circuit. It works totally fine.

I tried the same thing with that fan. However, the problem is that I can't run that fan in every delay time. It's understandable that fan does not work when I implement a long delay. Before every delay, I start fan with full speed for 10 seconds.

I can run the fan between 3.5-7 ms. I just don't understand why it does not work when I implement small delays like 1-1.5 ms.

Imagine I implement 1 ms delay. I run it with full speed for 10 seconds. After 10 seconds, it does not work properly. It makes noise and coil winding gets pretty hot.

Why am I facing this problem? Also how can I solve that problem ?

  • \$\begingroup\$ What kind of dimmer are you using? Your question suggests you're using a PWM-based dimmer, which would be ideal on something like a DC motor, however I think it will introduce additional problems here. A potentiometer-style dimmer might solve your problem? \$\endgroup\$
    – MrMeowMeow
    Nov 10, 2022 at 9:46
  • \$\begingroup\$ @MrMeowMeow I use potentiometer-style dimmer. \$\endgroup\$
    – Bowman
    Nov 10, 2022 at 9:49
  • \$\begingroup\$ Then what are your comments about delay? \$\endgroup\$
    – MrMeowMeow
    Nov 10, 2022 at 9:51
  • \$\begingroup\$ @MrMeowMeow It is about how much mains I let go through. \$\endgroup\$
    – Bowman
    Nov 10, 2022 at 9:56
  • 3
    \$\begingroup\$ Is the fan motor a universal style motor with brushes or an induction motor. Induction motors don’t like being phase controlled. \$\endgroup\$
    – Kartman
    Nov 10, 2022 at 10:39

1 Answer 1


Mains light dimmers intended for incandescent bulbs use phase control. The dimmer output is not turned on until later in each mains cycle, with the turn-on point set by the adjustment potentiometer. This delivers a chopped mains waveform to the bulb at the same mains frequency.

An induction motor's rotational speed and torque is set by the frequency and amplitude of the voltage across its two windings. The second winding uses a capacitor to add a phase shift to the applied voltage frequency. The motor speed cannot be adjusted by phase control. If you try, then it will run badly as the phase chopping is increased then stop when phase chopping reaches a small fairly amount.

Instead, induction motor speed would be controlled using an inverter to adjust the applied voltage frequency and amplitude.

  • 1
    \$\begingroup\$ You forgot to mention about rotor sliding in asynchronous motor. Motor speed is depends on load too. It can be controlled by changing effective voltage. But start current is 4-7 times higher then working current and OP probably tried to start motor with too low voltage and not enough current to start. \$\endgroup\$
    – user263983
    Nov 10, 2022 at 13:20

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