Then I remembered a few threads about people wanting to control the speed of their aquarium tank pump. Is it possible that these pumps use a shaded pole motor and can therefore be controlled using a lamp dimmer?
Obviously it's a bit late but I'd like to know in case someone asks the question in future.
These motors have only one winding, no capacitor nor starting switch, making them economical and reliable. Because their starting torque is low they are best suited to driving fans or other loads that are easily started. Moreover, they are compatible with TRIAC-based variable-speed controls, which often are used with fans. They are built in power sizes up to about 1/6 hp or 125 watts output. For larger motors, other designs offer better characteristics.
The basic shaded pole motors can be phase angle speed controlled but its more of a torque control effect that you are getting.
At no load they will tend to run at near their normal speed but when loaded down that where the limited torque gives it lower speed.
It basically just dropping the voltage so that the motor is limited to how much power it can produce. With a properly sized power factor control capacitor in parallel to the motor they will usually work rather well on a standard issue light dimmer.
Well since he wasn't around I thought I would try and answer your question any way.
The capacitor in parallel is bringing the power factor of the motor closer to neutral so that the triac can do its switching at the correct points on the sine wave. Without it most lamp dimmers are not able to handle the highly inductive load of a motor and burn out being they are designed to work only with a resistive load that has very little inductance or capacitance.
Then I remembered a few threads about people wanting to control the speed of their aquarium tank pump. Is it possible that these pumps use a shaded pole motor and can therefore be controlled using a lamp dimmer?
Obviously it's a bit late but I'd like to know in case someone asks the question in future.
The aquarium water pumps I have seen use synchronous motors. The armature is just a magnet and spins with the angular change of the incoming AC voltage on the field winding. Note: They do not like to operate off-frequency. ie: If designed for 60 Hz, do not work well at other frequencies. They are also finicky about voltage. Keep both Freq and Voltage within 10%. If you change either frequency or voltage, or drive with a square wave, they have trouble starting, and tend to make rattling noises as the impeller is not hard-fixed to the armature.
Fountain pumps for gardens are similar, just large aquarium pumps.