Circuit to vary speed of single phase syncronous motor

Thread Starter


Joined Oct 18, 2011
I want to make a chart recorder and want to have the paper feed run by a motor synchronised to the AC supply. I think that will result in good precision.

The speed of rotation of a single phase synchronous motor is a function of the drive frequency.

I'm wanting to vary the speed of a fractional single phase synchronous motor. That will require some sort of frequency converter.

Are there any circuits I can make? Thanks.


Joined Feb 12, 2009
It will require a frequency converter. Not an easy thing to make.

Have you thought of using a stepper motor? Easy to get, you can find them on old printers and disk drives. Not that expensive to buy new, either.

Fairly easy to build a circuit to step it very slowly. You can time it with a quartz crystal oscillator. A gearbox probably will not be needed because you can step the motor as slow as you want. For example, the motor might do 1 step a second, hour, day, etc. Good stepper motors have 200 steps per rev.

The electronics could use a small micro-controller (PIC) or could be built from logic ICs (CMOS, etc). The micro-controller method would be best because the motor speed could be adjusted with a simple code change or a switch could be added.

Thread Starter


Joined Oct 18, 2011
Well, I thought maybe somewhere someone might have concocted something. I was figuring that if I left the chart recorder going a week (say to take a weeks outside ambient temperature or barometric pressure) it might be best using a synchronous motor. But, even if it is best, not easy to make a circuit. Probably complex just to alter the frequency in multiples of the mains frequency, even more so to cater for variations in-between.


Joined Mar 14, 2008
A stepper motor is also a type synchronous motor and is much easier to drive than a standard sine-wave AC synchronous motor, especially at very low speeds. I also recommend you use a stepper.


Joined Nov 30, 2010
You could also buy a 7 day recorder. Grainger item number 5KE59 is the first in a whole page of 7 day recorders. Search for "seven day chart recorder".