AC single phase shaded pole induction motor

anilmanual@gmail.com wrote:

The torque-speed curve of an induction motor is a function of effective
rotor resistance, and also of slip. Your motor's no-load speed is very
close to 3600 rpm, so the rated speed represents 17% slip. (Some
high-performance induction motors would stall if loaded that much.)

Most shaded-pole induction motors that have speed controls drive window
fans and furnace blowers. The ones I'm familiar with achieve two or
three speed settings with a switched series inductor. Fan loads are easy
to control because a fan's torque goes approximately with the square of
its speed. You will find it hard to control your motor is the load's
torque is independent of speed. You will need an active servo to avoid
stalling below about 2000 rpm. With speed feedback, you don't need to
know the torque curve very well.

If you measure the torque-speed curve at full excitation, you will find
that is is small when the rotor is locked, rising as speed increases to
a maximum that depends on the effective rotor resistance, then falls to
zero at synchronous speed. The motor's steady state is always in the
falling region. If the torque is sufficient to drive the speed to the
peak of that region -- the peak available torque -- the motor stalls.
Obviously, the torque of your motor peaks comfortably below 3000 rpm.
maybe as low as half that.

If you use semiconductors to vary the speed, ensure that the circuit
delivers DC-free drive at all speeds and loads. DC in the stator will
drive it into saturation and overheat it.

Jerry
--
Engineering is the art of making what you want from things you can get.
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Think would be easier done with a VFD, DC or ECM control setup.

Jerry Avins wrote:

Dennis Mchenney wrote:

We don't yet know the application, speed range, stiffness requirement,
or much else. Note that without reverse torque available, some classical
servo schemes won't work very well.

jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Yes Yes, need more info for sure. But shaded poles not very good for
Torque control. Lots of low cost DC servo controls and motors in the
small size range and if he needs AC there are small single phase units.

He could also use the motor MAYBE and couple to his load with a shaft
mounted particle brake and use a strain gage arm to get torque feedback.

http://www.placidindustries.com/

Jerry Avins wrote:

Dennis Mchenney wrote:

Everything I can think of seems over elaborate for a 1/150th Hp motor.

Jerry
--
Engineering is the art of making what you want from things you can get.
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True enough. The big thing with the scenario as laid out by the OP, however,
is that a shaded pole motor has a very low efficiency, especially one that
small. You will probably find that there is almost no difference between
no-load current and locked rotor current.

If all he wants to do is reduce the (available) torque, all he needs to do
is reduce the voltage, and hence the air-gap flux, proportionally. The
inefficiency makes the rest of the details superfluous.

anilmanual@gmail.com wrote:


I can think of a lot of options other than shaded pole motors that would
be superior -- why this particular motor?  What's your application?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

If i use 3 phase ac induction motor .could suggest a method to control
the torque in closed loop.

Small VFD drive unit sized to your motor and torque requirements.

anilmanual@gmail.com wrote:

anilmanual@gmail.com wrote:

Two-phase induction motors with high enough rotor resistance to put the
peak of the torque-speed curve at standstill were standard servo motors
before transistors made DC drive practical. One winding has fixed
excitation, with the other driven in quadrature at variable amplitude.
Reversed phase provides reversed torque. There are more sophisticated
techniques available now, but they may not adapt well to such low power.

If you can choose the motor, why not consider a DC motor, PM or brushless?

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

anilmanual@gmail.com wrote:

I was really trying to lead you to Jerry's suggestion.

If you can monitor the motor speed you can control the torque by
controlling the motor current and slip speed per Dennis's suggestion --
but if you can monitor the motor speed then you can monitor the motor
position, and if you can monitor motor position then you can just use a
3-phase brushless with controlled current to much greater effect.

It would really help us help you if you could share the problem you're
trying to solve, rather than tossing up motor possibilities and asking
to do hard things with them.  If you're worried about
competition-sensitive information you don't even have to tell us that
you're making a left-handed frammelhultz glitzer.  You can just say
something like "I need to design a motor drive that must generate up to
20 N-m, with torque controllable to +/- 0.2 N-m and speeds between 0 and
2500 RPM".  Put down everything that's an issue -- price?  size?  is it
going into existing equipment?  etc.  If you give us _that_ sort of
information then we can help you with a solution.

And who knows, maybe your induction motor will be the right choice.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com