i have a dayton shaded pole single phase motor with 1/150HP, 3000
RPM, 230 V, 60 Hz frequency and Full Load Amps
0.24 . I want to control the torque of this motor through program.For
that i have input current to the motor as input. I
would like to know whether there is any equation connecting troque .
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.
If the motor is at stall, and yoiu oare using it as a torquer, then the
is essentially proportional to current or AC voltage applied. If you
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.
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?
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
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.
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
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
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.