Single Phase Motor Control

I would imagine that I get asked several dozen times a year about a VFC for
controlling a single-phase motor. Well, here it is in writing as far as what is
available at this time:

There is not one manufacturer building a single-phase input and single-phase output variable frequency controller, Not One. The only way to control the speed of a single-phase motor is via voltage control and this only works on certain motors. Voltage control as I am describing it in this document can be best identified as a “Dimmer Switch”. The only ones that work well are the Solid State type and are limited in use to just a couple of motor applications. They will not work on the following:

     - Capacitor Start type Motors

     - Dual Winding Motors (Start and Run) with speed engaged contacts

The above-mentioned are the most common type single-phase motors and if you try to control these with variable voltage, they will definitely burn up. These are the motors mostly found on Clothes Driers, Washing Machines, Drill Presses, Band saws, Table saws, Small Lathes, Air Compressors and so on.

Capacitor Start- Capacitor Run type motors have been used on variable voltage but I still don’t believe that these are reliable on variable voltage control as eventually, the capacitors overheat and wear out due to the lack of proper voltage applied to them.

Shaded Pole motors work well on variable voltage control but understand that these motors have very little starting torque to begin with; so using them with a variable voltage source will make them very, very weak when starting. These motors are commonly found in ceiling fans and will run little else. Next time you get the chance, pay close attention to a ceiling fan starting. You will notice that it takes it some time to get up to speed. That is because of its low torque, high slip characteristics.

I wish I had something to offer but I don’t think it will ever happen in my lifetime.


Scott

Merry Christmas and Happy New Year

Here it is, December 23rd and we are here hoping all is well with you and your families this Christmas.  Hoping that it has not been too hectic as this time of year can be for most of us.  It's mid-morning and I will probably turn everyone out about noon or so to start their Christmas holiday events.

I truly appreciate all of you and hope this coming year brings us all bigger and better things in our lives.  Well, at least more satisfaction than we expect and have enjoyed over this years trials, tribulations, travels and adventures.

Everyone, have a great holiday season and I will be in touch soon; next year!

Scott