AC shader pole induction motor

You have a very difficult problem. The reason is that the full load current might be only a 10 or 15% larger than the no load current and the locked rotor current could be nearly the same as the full load current. Speed, current, and torque are all interrelated. If there is some reasonable equation, you will have to derive it by testing. I suggest you use a DC motor, then you have a chance of success.

Randy

Right on, Randy! Besides all that, the very reason he broached the subject pretty well limits his chances of success, IMO.

If the motor is at stall, and yoiu oare using it as a torquer, then the torque is essentially proportional to current or AC voltage applied. If you let the motor get anywhere near synchronous speed, the torque becomes more challenging to predict. If you want to use this as a take-up motor for some kind of spooling application, it can work well, as long as the motor stays below, say, 1000 RPM.

Jon

anil---

I have a little paper back book titled Electrical Motors and Control Techniques, bu Irving M Gotlieb. It shows a nice graph of torque and RPM and current for a Shaded pole Motor. The text of this book says the shaded pole motor is well suited to speed control by variation of applied voltage. As *I* read the graph, the maximum RPM to be acheived thru voltage variation would be limited to about 4 percent of its max speed.

I dont understand what "connecting torque" refers to. Can you tell us more about what you are wanting to do?

Jerry

That's clever. I've never seen it done commercially, but it would be handy to maintain a constant tension on take ups of shrink wrap machines.It would be a lot more constant that the "bobbing arm" brake systems

Jerry,

I have to control the torque of the motor .For that i have the load current as feedback from motor.So for calculating the present torque and controlling the torque using the current i need a eqution .ie.Calculating torqe from the load current.

I posted induction motor equations a while back-I'll look around and see if I still have them...

hi, can u plz give me the equation for finding torque of a single phase ac inductiom motor.

You're going to have a very hard time controlling the torque of an induction motor by monitoring current--there's not going to be a simple relationship between current and torque. You might get some ideas by reading up on "torque motors" which are usually permanent split capacitor motors. Torque is controlled by voltage rather than current with these motors.

The Bodine Motor Handbook is a good place to start.

Induction motor equations involve parameters that you may not be able to readily measure. As others have pointed out, there is no simple solution as in DC motors. Depending on your mechanical system and response time you might be better off monitoring torque directly.

A shaded pole motor is a form of induction motor. Torque in such motors is a function of speed and rotor resistance as well as current. In a shaded pole motor it is also a fn of the shading pole resistance and phase shift.

Unless you are using the motor as a stalled torquer (zero speed), you will need to sense speed as well as current in order to control torque.

The relationship is quite nonlinear. If you are constrained to use a shaded pole motor, the best way to do this would be with direct torque feedback. Failing that, I'd suggest use of a lookup table with two-dimensional interpolation, using measured torque vs speed and current data from the motor at hand. It may be possible to infer torque from current and phase angle with no speed information, but again the relationship would depend on a number of parameters of the particular motor. Resistance-related parameters may vary significantly with motor temperature.

Things would be much simpler if you could use a DC permanent magnet motor, in which torque (including drag in the motor) is directly proportional to current regardless of speed or armature resistance.

If i use 3 phase ac induction motor ,could u suggest a method to control the torque with its current feedback.If it can't can u suggest a new method.

suggest

As numerous posters have suggested, use a DC motor...

See previous message.