I have a circuit where I am using triacs to switch home appliances like fan, tube light etc. This is the circuit I am using:
(TRIAC1, TRIAC2, TRIAC3 come from arduino GPIO pins)
First load is a fan with a capacitor based regulator. (Sorry for showing fan and tubelight as a resistor). Speed is controlled by rotating a knob which changes the series capacitance. Lower capacitance means lower fan speed.
As seen from the circuit, I didn't use a snubber because I thought using a snubberless triac will do the job, however the following incident made me rethink about the situation:
1) When Bulb and tubelight are off and fan is ON, and I try to regulate the fan speed by rotating the knob, sometimes there is a flicker in the tubelight and bulb. Flicker is very short lived but still visible. Flicker doesn't happen at higher speed. It usually happens at lower speed levels. For ex - There are these levels: OFF, 1, 2, 3, 4, 5 (5 means direct connection to Live). When I switch speed from 2 to 1 (or vice versa), I see a short lived flicker in the tubelight.
2) If the fan is running at low speeds - 1 and 2, and I try to turn the fan OFF by pulling the GPIO (TRIAC1) LOW, the fan won't turn OFF. Instead it produces humming sound and continues to rotate at a lower speed which indicates partial turn ON of triac.
Here is the fan regulator I am talking about:
Putting a RC snubber on triac 1 didn't solve the issue. Moreover I am using snubberless triac so I think it's not the inductive load that is giving me issues. The capacitor based regulator is the culprit here. Maybe LC circuit is going in resonance when regulator is set at low speeds and that resonance is giving me these issues.
If anyone could suggest something to get rid of this issue, I'll be very thankful.