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TRIAC compatibility
3

TRIAC compatibility

TRIAC compatibility

(OP)
I have been looking into controlling single phase 115v motors with a triac but have been finding issues like compatibilty, what i would like to know is what types of motors are compatible with a triac for speed control, any information is greatly appreciated

RE: TRIAC compatibility

Your triac will essentially vary voltage, but does not modify frequency. A universal motor is certainly controllable by a triac, and some special-purpose motors such as the external rotor types used on many fans can be crudely controlled by a triac, although the control is largely due to the behaviour of the fan load as speed drops being loosely compatible with a reduced voltage control. The motors are lossy and inefficient at low speed, but at the power levels involved it's not really a big problem (unless you have an awful lot of them!)
  

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If we learn from our mistakes I'm getting a great education!
 

RE: TRIAC compatibility

(OP)
thanks for the input, so then my next question is can i run, a capacitor start motor, split phase motor, capacitor start/capacitor run. Ive been told i can use a permanent splic cap. motor but i cannot seem to find one for what i need.

RE: TRIAC compatibility

No.
Not very well.
No.

What exactly are you trying to do?  What will the motor drive?

Keith Cress
kcress - http://www.flaminsystems.com

RE: TRIAC compatibility

(OP)
the motor im looking for is for and exhaust fan

RE: TRIAC compatibility

Universal motor as Scotty UK said, and in an exhaust fan, probably a Shaded Pole motor will work. No other choices if you stick with simple triac control.

If you look hard enough you can get a single phase (output) VFD, and with that you can use PSC motors. That's probably what you were hearing and whomever said that was misinterpreting your speed control method.

But for the price they will want for a single phase VFD and a PSC motor, it may be easier and cheaper to switch your motor to 3 phase and get an off-the-shelf common VFD that will convert 1 phase to 3 phase. It's inherent in the design and most small HP VFDs will not require any special sizing or modification to be fed with 1 phase power. If you are in North America, you can even get them that will take 115V 1 phase input and give you 230V 3 phase output (up to 1HP).

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RE: TRIAC compatibility

There are single phase motors with auxiliary capacitor that can be run off a triac controlled voltage. Very common in ventilation. Ziehl-Abegg produce such motors and controllers to go with them.

The rotors have high resistance and slip varies with voltage. Low efficiency? Yes. But, since torque is also low, it doesn't matter much. Actually, with auxiliary power suppply needed for a VFD, it is often more efficient to use a triac and voltage control with FHP motors.

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

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