What's special about fan speed controllers?

Inductive load maybe.

I used S&P units - not cheap but they are fan manufacturers.

Cheers

Dave R

Are they VFDs, phase controllers or ???? (Google hasn't been helpful)

Motor laminations avoid turning a bunch of 50Hz power into heat. When you greatly raise the frequency by chopping the waveform, that no longer holds true. Also motors depend on magnetic phase shift, which with some types is frequency dependant. When it is, messing with the frequency messes with the phase shift thus efficiency plummets, or it doesn't work at all.

NT

The circuit uses a snubber, when an (inductive) motor is connected.

One of the commenters asks a question about the motor noise.

They address VFD here a bit.

Compatible Incompatible

Permanent Split Capacitor (PSC) Split Case Shaded Pole Induction Motor Capacitor Start AC Synchronous Repulsion Induction Series Universal (AC/DC) Any motor with starting switch (centrifugal or relay) Any motor with separate starting winding "

They talk of derating, which means the temperature increases as you abuse the motor.

There are permanent split capacitor motors with taps for speeds. They're used as blower motors for air handlers. You select the tap for the speed you want and apply power there.

There are smaller versions of those, but probably not small enough for your application (1/10th to 1/20th HP).

There are some motors that run insanely hot. Exactly how the wire insulation holds up (enamel) is really hard to guess. You cannot use an alternate insulation (say asbestos) without adversely affecting turns count. The motors run hot enough, to burn up the lubricating oil.

Another kind of solution would be a DC motor. And with a governor, depending on motor type and how load sensitive it is. Preferably brushless, for a long life.

Paul

If its synchronous you need a variable frequency drive.

People talk about "electric motors" like as if they're all essentially the same basic design. They're NOT. There are so many variations and unless you know exactly what type your dealing with, it's impossible to say which type of speed controller - if any - will work with that specific motor.

well in a sense they are all; the same in basis. They are a;l synchronous, but those with commutators use the commutator to generate the synchronicity..

And all follow the basic rule that they cant go faster than the applied voltage will let them, unless they have variable magnetic fields.Series would field coils being an interesting example.