Dimming Thermostat - general questions

[HenrikOlsson]

Hi,
I created the following picture to further illustrate the issue with running a "normal" PWM signal into a triac or a random firing or random turn-on SSR:



I choosed a random PWM frequency (which was easy to draw) relative to the 60Hz mains but it doesn't really matter.
The triac/SSR is ON during the purple sections which, as you can clearly see, is a lot more than the 12% dutycycle of the PWM signal.

I hope this helps illustrate my point.

/Henrik.

[amgen]

you have 120- half cycles per second that you can cycle....... you can break that down to 60/half second or 30 per quarter second....... if you consider controlling for 4 times a second, then you can go from 1 cycle on and 29 cycles off up to the opposite on/off ratio.......
that's 250 milliseconds each control loop.....so say 10 milliseconds on pulse and off 240 milliseconds for minimum......
that's just pin hi, pin low functioning with some kind of counting loop and changing the ratios accordingly....
That would use a zero-crossing SSR for ease of use.
There could be a I cycle error unless you use some kind of zero cross detector to sync up...... probably not necessary because the error would probably average out.

[Scampy]

Henrik, thanks for the detailed explanation...