Anybody know how a 2 speed commercial fan motor work. (Single phase, 1/2 hp, 7.1 Amp, 115v with 17.5 mF cap.)

Question

I sort of know how a single speed motor work, but how does a 2 speed motor work. I wired a motor at work today, and I was curious how the windings inside are wired. There's an orange wire for the high speed, a blue wire for the slow speed, and a white wire that connects to the neutral. Then there's a 3 position pull switch ( L1 is connected to common, orange and blue is connected to other 2 contacts) .Anyways, the first pull is for high speed, which will allow current to pass through the orange wire and through the windings, and out through the neutral. The second pull is low speed, which will disconnect the orange wire and allow current to pass through blue wire, and of course neutral. I had a class in school about motors, but forgot about multi speed motors. Lazy to go through my books.Someone please refresh. Thanks

Answer 1

your changing the amount of magnetic field by the amount of windings you use, so for instance your high speed wire has a lot more coils in the motor and your low does not

Answer 2

If it's just just for a fan, and it's switching to a completely different circuit like you say, then my first guess would be that the lower speed probably just taps into the main winding at another point, effectively reducing the loops in the motor... and that the cap might just optimize consumption for only one of the speeds. I expect that it is a cap-run motor for a fan application.

Edit:  There are of course better (and cooler) ways to make a multi-speed motor though, but it doesn't sound like your case uses one of them... especially if it's just a two speed thing.