Are all ceiling fans AC induction motors?
Since any ceiling fan can accept any off-the-shelf fan dimmer switch and any wireless remote unit that fits in the base, that means they've all got something in common and the way to control the motor speed is similar among all fans.
What is the mechanism used to control the fan speed for a fan dimmer switch vs a 3-speed wireless remote? Do they use the same mechanism? Are the electronics and method of control universal?
They are generally controlled by switching between 3 different in-series capacitances. Full power is shorted/0F. The other two appear to add reactance to the circuit in series which is an a/c resistance at 60Hz thereby lowering the power reaching the fan.
I've seen mention that another way would be to select between the number of coils on the fan motor itself, but I'm not sure how prevalent it would be.
Also review the top answer here for some more background.
Induction motors? all the one's I've seen are.
friction controls the fan speed. Seriously, take the blades off and see what effect the "speed control" has.
The "speed control" is actually a torque control it limits the current that can flow into the motor, the motor is thus weaker and cannot drive the fan blades at full speed.
Switched capacitors, or dimmer-like active electronic circuits are used to effect the current limit.
Different speeds via capacitor changes is for multi fixed speed fans, not variable speed via dimmer.
Friction control? In a very indirect way, I suppose. The witnessed phenomenon of the fan rotor speed increasing if the fan blades are removed is explained below.
Torque control? Nothing that sophisticated, but that is the net effect yes.
The dimmer works to reduce the net average VOLTAGE going to the motor. That in turn reduces the torque that the motor can produce by the square of the voltage reduction. So at 50% voltage, the motor produces a maximum of 25% of rated torque. Then because the fan blade pitch is fixed and the air density doesn't really change, there is an EFFECTIVE change in the speed of the fan, because the reduction in torque capacity in the motor means it increases the "slip" of the motor. Slip is the difference between the speed of the magnetic field rotation (determined by the line frequency) and the actual speed of the rotor; higher slip means a greater difference, ergo slower rotor (blade) speed. Slower blade speed = less air movement, air movement = load, load x time = energy, so lower energy use.
If you remove the fan blades, the rotor speed increases because there is no no load on that motor other than it's own mass, so it is not doing any useful work.
