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single-phase motor speed control

Andrewxxd1

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Hi all. I hope you can answer my concerns and that the possible answers are helpful to other people

I am considering the possibility of controlling the speed of a single-phase motor, my question is, can all single-phase motors have speed control? Of course, there is a wide variety of single-phase motors, such as the auxiliary starting coil, capacitor starting, permanent capacitor, permanent capacitor with starting capacitor, and surplus turns.

What would be the best option to control the speed of any of those motors?

I know that three-phase motors can be controlled by a frequency inverter (I have).
The issue is that I have never worked with single-phase motors and I don't know if there is any frequency inverter that works for this type of motors.

I have seen an infinity of videos that use a dimmer "angle trigger controller with TRIAC", to control the speed of some motors, the doubt that also arises, how effective is that type of control ?, considering that it varies the input voltage but not the frequency, I tend to think that this could cause engine torque problems at low revs.

What is the difference between controlling the speed of a motor by varying the input voltage, or varying the speed?

In case there are frequency inverters for single-phase motors, which one do you recommend? (voltage 220v 50Hz).

The dimmers I have seen on AliExpress say they are from 5000W to just 11 dollars, that is why I have this doubt which would be better to apply for a small business job. for example a wood cutting bench
 

schmitt trigger

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There are many single phase induction motor architectures.

Some of them use auxiliary windings and/or start capacitors, which are connected at standstill during startup and disconnected by a centrifugal switch as the motor gains speed.
These devices are only rated to operate for a few seconds and then disconnect. If you operate them continuously, they will be damaged.

If you lower the motor speed to much, the centrifugal switch may re-connect the auxillary winding and start capacitor. Damage will result if the motor is left running in that connection.
 

FvM

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See https://www.invertekdrives.com/variable-frequency-drives/optidrive-e3-single-phase/
See this previous thread https://www.edaboard.com/threads/2-phase-vfd-design-for-conventional-split-air-conditioner.344273

Basic disadvantage of single-phase (actually two-phase) motors is pulsating torque which restricts the operation at lower speed.

Variable voltage/current control of single phase induction motors by dimmer, variac or variable resistor is only useful for drives that are stabilized by a speed dependentload torque e.g. fans or centrifugal water pumps.
 

Easy peasy

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Yes you can speed control a single phase motor - you need a LARGE TRIAC - ( or back to back SCR's ) with snubbing and careful consideration of starting ....
 

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