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Single phase AC motor speed control

J

Joe Legris

Jan 1, 1970
0
Richard said:
Hi

I intend to construct use a PIC to control the speed of a single phase <100W
AC motor but have not much idea how they are controled? Could it be
controled by Phase Control just like some light dimmers?

Any ideas?

Thanks

Regards,
Richard

What kind of motor is it?

In some appliances, such as hair driers, there are permanent-magnet DC
motors with a full-wave rectifier. You can easily control them with PWM.

Induction motors (synchronous or otherwise), require variable frequency
AC power for speed control.
 
R

Roger Hamlett

Jan 1, 1970
0
Richard said:
Hi

I intend to construct use a PIC to control the speed of a single phase <100W
AC motor but have not much idea how they are controled? Could it be
controled by Phase Control just like some light dimmers?

Any ideas?

Thanks

Regards,
Richard
You need to find out a _lot_ more about your motor.
There are many different types of single-phase AC motor (capacitor start,
shaded pole, split phase, and synchronous), are 'common' designs. Many of
these will not speed control easily at all, and all will lose torque very
quickly, if you attempt to speed control them. Some will need the actual AC
frequency to be changed to give speed control (the synchronous design).
Many motors used on things like vacuum cleaners, are a design known as the
'universal' motor, effectively being a series stator/commutator design,
which will work on both DC and AC. These can be power controlled, by
reducing the peak voltage, and speed will reduce (depending on the load), as
the power is reduced.
You can't even 'start' to think about speed control, till you know what sort
of motor is involved.

Best Wishes
 
R

Richard

Jan 1, 1970
0
Hi

I intend to construct use a PIC to control the speed of a single phase <100W
AC motor but have not much idea how they are controled? Could it be
controled by Phase Control just like some light dimmers?

Any ideas?

Thanks

Regards,
Richard
 
T

Tim Jackson

Jan 1, 1970
0
Richard said:
Hi

I intend to construct use a PIC to control the speed of a single phase <100W
AC motor but have not much idea how they are controled? Could it be
controled by Phase Control just like some light dimmers?

Any ideas?

Thanks

Regards,
Richard
You -can- get a certain amount of control this way for things like fans and
pumps which have a nice progressive load, as long as you don't want to go
too slow. You are controlling torque rather than speed. I designed a fan
controller for a filtered laminar flow 'fume cupboard' (for toxic preps)
this way which worked fine, but I knew the fan would never be called upon to
deliver less than half power.

If you go lower several things go wrong. The motor becomes very
inefficient, and so gets hot. If is cooled by an on-shaft fan (or -is- a
fan) then its cooling will also reduce, just as its heating is increasing.
Also there is increased vibration which shortens the bearing life. I had
one fan manufacturer revoke their guarantee if their fan was driven in this
manner.


Tim Jackson
 
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