Speed Control of single phase shaded pole motor

Thread Starter

daelinparmanand

Joined Mar 31, 2021
15
I have a group project where I have to control the speed of a single-phase shaded pole induction motor. My plan was to use a Triac-based circuit however, all Triac circuits I have seen use a potentiometer to control the speed of the motor. In this project, the motor's speed is dependent on an external analog signal received from another unit. The 3 signals can either be high, medium, or low. How can that external analog signal be received and used to drive the motor at the specific high, medium, or low?

NOTE: No microcontrollers may be used
 

SamR

Joined Mar 19, 2019
3,424
Start by diagraming it out, blocks at first which may then be expanded into circuits. Annotate all known variables and list unknowns.
 

SamR

Joined Mar 19, 2019
3,424
Baby steps, blocking out the problem helps to understand the big picture and then focus on the details.
 

Thread Starter

daelinparmanand

Joined Mar 31, 2021
15
Check out the Fairchild app notes, AN-3006 also AN-3003
Shaded pole motors are not the best candidate for speed control.
Hi max, I've seen the AN-3006. Since the speed is not manually controlled, is it possible to remove the 10k VR1 and use the LM555 timer to receive a reference voltage?
 

LowQCab

Joined Nov 6, 2012
588
Here's several important hints .......
You can only reliably control the speed of a Shaded-Pole-Motor by varying the
Frequency of the AC Voltage applied to it.

And, (Bonus Hint), a Shaded-Pole-Motor will run on a Square-Wave,
at reduced Voltage, with around ~50% reduced Torque output.
( too much Voltage with a Square-Wave will cause over-heating )

And, a Square-Wave can easily be smoothed into a fair approximation of a Sine-Wave.

And, a Bridge-Rectifier puts out a pulsating DC-Voltage
at exactly twice the Frequency of the input AC-Voltage.
A pulsating DC-Voltage can be run through a Capacitor,
which will change the output back into an AC-Voltage, (some smoothing will be needed).

As the AC-Frequency increases, the inductance of the Shaded-Pole-Motor increases,
this will automatically reduce the Current draw by the Motor's Winding,
allowing higher Voltages, without over-heating the Motor.

I suggest going for Half-Speed, Normal-Speed, and Double-Speed.
 

Thread Starter

daelinparmanand

Joined Mar 31, 2021
15
Here's several important hints .......
You can only reliably control the speed of a Shaded-Pole-Motor by varying the
Frequency of the AC Voltage applied to it.

And, (Bonus Hint), a Shaded-Pole-Motor will run on a Square-Wave,
at reduced Voltage, with around ~50% reduced Torque output.
( too much Voltage with a Square-Wave will cause over-heating )

And, a Square-Wave can easily be smoothed into a fair approximation of a Sine-Wave.

And, a Bridge-Rectifier puts out a pulsating DC-Voltage
at exactly twice the Frequency of the input AC-Voltage.
A pulsating DC-Voltage can be run through a Capacitor,
which will change the output back into an AC-Voltage, (some smoothing will be needed).

As the AC-Frequency increases, the inductance of the Shaded-Pole-Motor increases,
this will automatically reduce the Current draw by the Motor's Winding,
allowing higher Voltages, without over-heating the Motor.

I suggest going for Half-Speed, Normal-Speed, and Double-Speed.
.
.
.
Thank you! I will take into consideration these tips
 

MaxHeadRoom

Joined Jul 18, 2013
23,150
Hi max, I've seen the AN-3006. Since the speed is not manually controlled, is it possible to remove the 10k VR1 and use the LM555 timer to receive a reference voltage?
That should be possible, BTW, I have several shaded pole motors here, mostly fan applications, ceiling fans, air exchanger fans all ran with Triac control.
But they are the lowest efficiency motor of all AC motors.
 

LowQCab

Joined Nov 6, 2012
588
You can make a "Synchronous" Motor run "out-of-Sync" by applying enough
mechanical Load to the Shaft.
A large set of fan blades could supply that excessive load,
but if it is not designed to run continuously in that condition,
it could overheat rather quickly.

The "no-load", "free-running", "Synchronous" RPM of the Motor
can only be altered by the AC-Power-Frequency.

When driving the calculated load that the Motor was designed for,
reducing the Voltage to the Motor enough, will, of course,
cause the Motor to slow-down and run "out-of-Sync",
and the only reason the Motor does not burn-up,
is because the Voltage has been substantially reduced,
which equates to much less Wattage being consumed by the Windings.

The Motor may not be able to "self-start" with substantially reduced Voltage,
but it may continue to run if you spin the Motor by hand.

At a any RPM other than the "Synchronous" RPM, (which depends on the AC-Frequency),
the Motor will loose efficiency very quickly,
(and it didn't have very much efficiency to start with).
Less efficiency = less work done, and more waste-heat.

.
.
.
 

Thread Starter

daelinparmanand

Joined Mar 31, 2021
15
That should be possible, BTW, I have several shaded pole motors here, mostly fan applications, ceiling fans, air exchanger fans all ran with Triac control.
But they are the lowest efficiency motor of all AC motors.
Hi Max, do you have any idea what has to be done with the LM555 timer to receive a reference voltage instead of using the 10k VR1 potentiometer?
Note:
Vcc is 5V
The source of the reference voltage is another unit known as the Speed reference unit where an output voltage in the region of 0-5V (reference voltage) is produced.
 
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