Rheostat on single phase induction motor

[Brad1979]

Can you use a rheostat to control the speed on a single phase(PSC), fractional horsepower motor? If so, how does it control speed without changing the frequency?

 

[Skogsgurra]

You can do it on motors with a high rotor resistance. You simply increase slip when you change voltage. A triac or a transformer with taps (or Variac) is more often used than a resistor. Suitable for fans and ventilators where power is speed^3

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[OperaHouse]

If you lower voltage you will increase slip. You are not controlling speed. Not practical at all.

 

[Skogsgurra]

It is being done all the time.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Compositepro]

As Gunnar said, it is a pretty common method to control fans (like ceiling fans). The torque required to turn a fan increases very rapidly with speed so a rheostat (or capacitor) which limits torque will reduce speed. The high rotor resistance keeps the motor from overheating at high slip.

 

[electricpete]

Stator side resistor works for NEMA Design D motor which has a curve of torque vs slip which is monotonically increasing.
Would not work nearly as well with typical NEMA Design B motor with a breakdown torque peak a few percent below sync speed.

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(2B)+(2B)' ?

 

[itsmoked]

Brad even though it's done on fans that doesn't mean it will work in any other application - it won't. However you haven't said what your application is.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Brad1979]

Thanks everybody. This is for a fan application.