I am using traic based dimmer circuit for regulating my ceiling fan. when the fan is regulated to low speed the other loads(incandescent,tube light,LED) in the room are flickering. when i increase the fan speed to certain level the flickering stops. i've tried using same circuit in my friend's home. Everything works fine(No flickering observed). I am observing this flickering at low speed let say value of 40% power

Used components: Traic : BT137/BTA24 opto coupler : MOC3023enter image description here

can any one please suggest me the solution . thank you.

  • \$\begingroup\$ What generates the PWM signal? \$\endgroup\$
    – bobflux
    Dec 31 '19 at 12:50
  • \$\begingroup\$ esp32 generates the pwm signal and ULN2803 controls the MOC gnd. i.e pin 2 shown in above circuit as "signal". \$\endgroup\$ Dec 31 '19 at 12:56
  • \$\begingroup\$ What frequency is the PWM signal? \$\endgroup\$
    – rdtsc
    Dec 31 '19 at 13:06
  • 1
    \$\begingroup\$ If PWM signal is not synchronized to mains, you'll have a beat frequency which is probably the cause of your flicker... Motor could also make weird noises. \$\endgroup\$
    – bobflux
    Dec 31 '19 at 13:07
  • \$\begingroup\$ What wonders me is that the same circuit board works even at low power levels i.e high fequency pwm signal in my friends house.I am facing this problem only at my place \$\endgroup\$ Dec 31 '19 at 13:45

Triacs cause harmonic distortion of the current used by the fan. If that current is a high proportion of the current used in the circuit and the circuit is near capacity, the current distortion can cause voltage distortion. The voltage distortion can cause flickering of the lighting. The difference in the two location is likely that the flickering location has lower current capacity and/or longer wiring distances compared to locations where there is no flickering.


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