FAN (220V AC) Speed control

you guys are not getting me again..

AC dimming or AC speed control is totally different from the DC concept of PWM.

in AC, the speed is proportional to amount of energy given to fan/bulb. which is again proportional to the area under the curve of AC voltage. e.g. here i shows a figure where three AC channels are switched at different times. you can see the AC wave delivered to the device is lesser than the original AC (Yellow curve). so the area under the AC curve is different in all cases and hence your o/p voltage varies... there is no PWM remember..

Ajay thank you for your help.

I guess i understand the concept of speed control of Fan better now.

Is it possible to generate 3 independent PWMs to control three separate fans each having different speeds using a single 8051 controller?

Also how would i be detecting zero crossing of triac (In case my approach is correct).

Ajay i have seen your Home Automation software and how you use "lwidth" for generating PWM. I want to do similar thing but i need to generate 3 PWM as mentioned in my post above.

Also is it necessary to detect zero crossing of triac or can i go around controlling fan speed even without it?

Sorry i am not good with electronics

For a small device like a fan, zero crossing is not really needed.
That is assuming that on/off times are much longer than a single mains cycle.

>Is it possible to generate 3 independent PWMs to control three separate fans each
>having different speeds using a single 8051 controller?
As your on/off periods are fairly long, an 8051 you should be able to create
at least three PWMs using built in timers and software counters.

Thank you sir

Can you please let me know how to generate PWM signals (Calculations) for generating a PWM with 100%, 50%,25% powers.

I believe that the image posted by Ajay has these all three PWMs init already. Seems like red graph shows 50%, blue 30% and yellow for 100%

Actually the image shows power control over a single mains cycle.
The PWM method I would use would be on for several cycles and off
for several cycles.

Please refer following two circuits

Here i have a sample that i found. Its kinda like what i want to build.

http://hobbykits4u.net/remote-dimmermotor-controller-p-45.html

Ajay can you please let me know how you generated the result in oscilloscope, i have tried but my results dont come out to be like yours

well, you need to code that way. follow this thread.

http://www.8051projects.net/forum-t28530-last.html