Hi folks,
I'm working on an invention that requires a 120v ac fan speed control regulated with a micro controller. I am a electronics hobbyist and certified electrician. I have found a circuit that might work for what I need, just need a little guidance with a couple things. Here's what I have so far.

-First of all, before I build this thing, can anyone tell me if it would work? Why not?

-What is the function of the capacitor? Is it necessary?

-Is there a better way to achieve my goal?

-Is there a more appropriate source for this information?

Any tips are much appreciated, thank you.

(just learning Fritzing in case my formatting is strange)

 

R2 & C1 is a RC Snubber used to reduce harmonics or switching noise created when the Triac switching.
Max.

 

Thanks Max, it's an honor.

So the snubber allows this circuit to be used with an inductive load correct? So theoretically if everything is rated correctly this should work?

 

Pretty typical tried and true circuit.
Max.

 

I'm new to a couple of these components, what kind of power rating would I need for R1, R2, & C1 if my Fan is 100w? I wouldn't need to match the fan power if they are in parallel with the triac do I?

 

R1 1/4w R2 1/2 w for the resistors, 200v cap AC rated.
Max.

 

-First of all, before I build this thing, can anyone tell me if it would work? Why not?

Might be wrong about this so someone may set me straight. @MaxHeadRoom

The circuit will work for a fan using a universal motor, one with brushes. But if it is an induction motor I don't think it will work. You didn't state the type of motor in the fan so just brought this up.

 

They do work with the shaded pole type ceiling fan motors, I have a couple in my place, they just use the normal 'dimmer' switches.
Max.

 

Thanks for coming in Max. Just didn't want him to try it with an induction motor.

 

Also see Fairchild AN-3003 AN-3006.
Max.

 

Thanks for coming in Max. Just didn't want him to try it with an induction motor.

Actually a Shaded pole is a form of induction motor.
Just uses a shorted turn/coil instead of a cap.
Max.

 

Thanks guys, I'm not too sure excatly which motor I'm going to use yet, so this helps a lot.

What would be the specs for the coil if i were to be using a shaded pole motor?

 

A shaded pole motor already has the shorted turn/coil on the stator, it just consists of a single turn of ~12g copper wire etc.
Also Triac controllers for inductive loads often have a Ferrite choke in series with the motor, it often consists of a 1" length of ferrite rod with a single layer of 14g enameled wire wound on.
Max.

 

Thanks again for the tips. It's really motivating to find the help I need for my prototyping, and encourages me to give back to the open source community when I've finally developed my project.

 

Thanks for coming in Max. Just didn't want him to try it with an induction motor.

How can I get this to work with induction motors?

If I use zero cross pulse detection to program when to fire the triac, should that solve it?

 

How can I get this to work with induction motors?

If I use zero cross pulse detection to program when to fire the triac, should that solve it?

Not with a standard induction motor, like in a washing machine or a dryer. Or for that matter a standard window fan. Now the shaded pole motor Max talked about, yes like a desk fan. A regular induction single phase motor the speed is set by the AC frequency and the number of coils in the stator of the motor. To get an induction motor that can be speed regulated, it takes 3 phase and VFD. The VFD changes the frequency going into the motor. VFD's don't work with single phase. Well that isn't quite true, because there is a company doing it now I understand but they are expensive.

 

How can I get this to work with induction motors?

If I use zero cross pulse detection to program when to fire the triac, should that solve it?

If using zero cross and burst firing i.e. period on-period off, you may get some results, but a little clumsy and I have not tried it with a motor, just element/heating.
You also may get some heating of the motor.
You can get away with it with shaded pole induction motor as the rotor is relatively small and possesses low inertia.
Max.