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Rheostat on single phase induction motor

Rheostat on single phase induction motor

Rheostat on single phase induction motor

(OP)
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?

RE: Rheostat on single phase induction motor

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

RE: Rheostat on single phase induction motor

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

RE: Rheostat on single phase induction motor

It is being done all the time.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Rheostat on single phase induction motor

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.

RE: Rheostat on single phase induction motor

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.

=====================================
(2B)+(2B)' ?

RE: Rheostat on single phase induction motor

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

RE: Rheostat on single phase induction motor

(OP)
Thanks everybody. This is for a fan application.

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