# Single phase universal motor, variable frequency (controller)

#### Cosmin1337

Joined Mar 22, 2021
4
Hello there!

I need some help regarding my final project for the university. I have a universal motor, supplied by a single phase, 220V source. I need to make this motor work at the same voltage, but to change the frequency between 20Hz and 60Hz.

If you have any idea how I can do this, I would be honored to hear your thoughts.

Thank you and have a nice day!

Joined Jul 18, 2013
22,855
What are you trying to achieve? Speed change?
The frequency is not going to make an big difference with a Universal motor, it is a series field motor and can run on AC or DC.

#### Cosmin1337

Joined Mar 22, 2021
4
I am trying to keep the same voltage and to control the speed regarding by frequency.

I need some books/pdf/articles regarding my project. Anything that can help me is very useful.

Joined Jul 18, 2013
22,855
You need to confirm the technology of the motor, i.e. is it actually a Universal motor or a AC induction motor?
If this is a 1ph Induction motor, they do not control at all well by change of frequency, they have a tendency to drop out of run under-load at low rpm.

#### Cosmin1337

Joined Mar 22, 2021
4
You need to confirm the technology of the motor, i.e. is it actually a Universal motor or a AC induction motor?
If this is a 1ph Induction motor, they do not control at all well by change of frequency, they have a tendency to drop out of run under-load at low rpm.
It's a A.C. supplied, universal motor. My professor gave me this project and I have 3 months to make this project true.

Joined Jul 18, 2013
22,855
I am still suspicious of it being a Universal motor, Does it have brushes?
If it is the case, then changing the frequency is not going to achieve anything!
What is the desired outcome??

#### crutschow

Joined Mar 14, 2008
27,004
As Max said, you cannot change the speed of a universal motor by changing its frequency.
It can run or AC or DC so ignores any change in frequency.

#### Delta prime

Joined Nov 15, 2019
843
Hello there If you're lucky the specification plate is on the motor it's self. If you can take a couple photos of the motor so we can guide you in the proper direction.

#### cmartinez

Joined Jan 17, 2007
7,313
The only way I can imagine frequency (assuming also a constant voltage, either AC or DC) would be involved in the control of a universal motor is if it were to be PWM'd ... in that case, frequency would indeed be relevant, although the most important factor would be the duty cycle, of course.

#### Danko

Joined Nov 22, 2017
1,070
How universal motor works:
Youth today believe in youtube only...

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#### crutschow

Joined Mar 14, 2008
27,004
The only way I can imagine frequency (assuming also a constant voltage, either AC or DC) would be involved in the control of a universal motor is if it were to be PWM'd ... in that case, frequency would indeed be relevant, although the most important factor would be the duty cycle, of course.
Don't understand the comment about frequency.
The primary factor is the PWM duty-cycle, with the frequency having only a slight effect over a large frequency range.

#### cmartinez

Joined Jan 17, 2007
7,313
The primary factor is the PWM duty-cycle
100% agree
with the frequency having only a slight effect over a large frequency range.
It does have a slight effect. But I've pwm'd 90VDC motors in the past, and frequency significantly affects their performance. They behave a little jerky if it's too low (below about 7kHz) and run smoother but start losing torque when too high (above 14kHz)... that at least has been my experience.

Joined Jul 18, 2013
22,855
The OP states it is a universal motor supplied with 220v AC. to be controlled between 20Hz & 60Hz.
With PWM, the frequency does not vary.

It's a A.C. supplied, universal motor. My professor gave me this project and I have 3 months to make this project true.
Was the term 'universal' used to actually describe a brushed AC motor?
He's needs to question his professor on this!

#### Cosmin1337

Joined Mar 22, 2021
4
The motor is a brushed series motor that works in DC and AC.
I want this motor to work in AC, at 220V.

The motor has max. current Imax=5A
Maximum output speed n=2200 RPM
The stator+rotor resistance R=5 ohms

I also searched on some books and on internet that i need a single-phase rectifier, and a power inverter. Then I need to PWM my transistors from the inverter to modify the duty cicle to make this possible.

I will attach a scheme I made. But I need more help from you guys! I don't know what rectifier and what inverter to use and how to pwm my transistors. Thank you.

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Joined Jul 18, 2013
22,855
You could also do it simply, how it is commonly done to work on 220vAC is with a simple Triac controller, being a series motor it is very hard to control accurate RPM control, it has been done with a Triac and a revolution sensor for feedback to the controller.

Joined Jul 18, 2013
22,855
I will attach a scheme I made. But I need more help from you guys! I don't know what rectifier and what inverter to use and how to pwm my transistors. Thank you.
You have a full wave bridge, but that will not provide reverse of a series motor, you need to reverse the field WRT the armature.

#### MisterBill2

Joined Jan 23, 2018
8,459
A cheating trick to vary the speed of the universal motor would be to put a capacitor in series with the power feed. As the frequency changes the impedance will change and thus the voltage on the coils and so the speed will vary.
Note that this is not an efficient way to controlspeed and probably not practical. But it would be simple and if there are no hidden additional requirements it may be adequate.