Hi there. I’ve built a power control circuit to control the speed of a fan (schematic attached). I’m a newbe at this so please forgive the simplistic questions. I have two fans. One of them, rated at .42 amps works perfectly. The other, rated at 1.1 amps starts to falter once the triac starts delivering about 74% of each phase of the sine wave. On advice from another I looked at the zero cross timings. This is North American current, so zero cross should happen ever 8333 microseconds. While things are well behaved, I’m seeing a variance of +/- 30 microseconds on the zero cross events. Once we reach about 74% power, the variance goes up to roughly +/- 100 microseconds. I’m not entirely sure if that explains the behaviour I’m seeing or not.
Thoughts? Could it be noise from the inductive load messing things up? Do I need a snubber circuit in front of the H11AA1? Unfortunately I don’t have a scope to dig deeper.