# Control Circuit for a single phase induction motor

1. ## Control Circuit for a single phase induction motor

Hello guys,

I am trying to build a control circuit for a single phase induction motor. How do I go about doing this?
This motor will be powered by battery. So I would need an inverter as well. The circuit needs to be able to control the speed of the motor using VFD.

thanks

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2. ## Re: Control Circuit for a single phase induction motor

Search on "H bridge" and "PWM" within this forum. Single phase motors are not designed for variable frequency use.
Frank

3. ## Re: Control Circuit for a single phase induction motor

Hello guys,

I am trying to build a control circuit for a single phase induction motor. How do I go about doing this?
This motor will be powered by battery. So I would need an inverter as well. The circuit needs to be able to control the speed of the motor using VFD.

thanks
You can have a bit search around the forum about it . but for now :
you have two way . first one an analog way and 2nd one is a digital way .

Which one you're interested in ?
i.e : for more help please mention your exact required specifications .
Best Wishes
Goldsmith

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4. ## Re: Control Circuit for a single phase induction motor

To change the RPM in an induction motor, you have to change both frequency AND voltage. This is what a VFD does.

1) Motor power
2) Motor nameplate voltage and frequency
3) Battery's DC voltage and capacity
4) Is the motor capacitor-satrted? Does it have an additiona "run" capacitor?

5. ## Re: Control Circuit for a single phase induction motor

To change the RPM in an induction motor, you have to change both frequency AND voltage.
Hi schmitt trigger

Not at all of the induction motors ! just squirrel cage motors !

Best Lucks
Goldsmith

6. ## Re: Control Circuit for a single phase induction motor

We are talking about single-phase motors.

For single phase AC, there are only two types of motors:
Squirrel cage induction,
and series wound universal, where both the rotor and stator have windings.

For polyphase motors, there are other variants like wound rotor induction (not to be confused with a series wound universal) or synchronous.

Regardless whether it is wound rotor or squirrel cage, all induction motors should be operated at a constant volt/hertz ratio to prevent magnetic saturation. Therefore, if a motor nameplate lists 240V/50Hz, to reduce its speed in half, one would apply 25 Hz, but the voltage would have to be reduced to 120 volts.

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7. ## Re: Control Circuit for a single phase induction motor

We are talking about single-phase motors.

For single phase AC, there are only two types of motors:
Squirrel cage induction,
and series wound universal, where both the rotor and stator have windings.

For polyphase motors, there are other variants like wound rotor induction (not to be confused with a series wound universal) or synchronous.

Regardless whether it is wound rotor or squirrel cage, all induction motors should be operated at a constant volt/hertz ratio to prevent magnetic saturation. Therefore, if a motor nameplate lists 240V/50Hz, to reduce its speed in half, one would apply 25 Hz, but the voltage would have to be reduced to 120 volts.
Schmitt trigger , of course i'm familiar with concept of motors as well . universal motors would be fine with only voltage controlling method . do you know why squirrel cage motors are requiring both V and F control ? i'm talking about technical reason behind that . if no refer tot he electrical machinery books which are dealing with these simple things !

By the way do you know why those motors have been called squirrel cage motors ? it would be fun if you investigate about it ! ( i know it but if you don't know i can explain it for you ! )

Best Wishes
Goldsmith

8. ## Re: Control Circuit for a single phase induction motor

When a motor its windings produce back EMF which is almost the same as the applied voltage, the difference is what is producing the current flow to overcome resistive losses. The back EMF is proportional to the change of magnetic field times the current flowing. So Vapp = Dmag//Dt X L + I X r . So halving the frequency will produce half the back EMF and will therefore almost double the current through the windings which will saturate the magnetic core, leading to much larger losses, not to mention over heating the conductors. Doubling the frequency has the opposite effect, there is much more back EMF, so to get the correct current you need more applied voltage.
A squirrel cage motor, is called this because its rotor's active part is a lot of parallel conductors with a short circuit put across their ends, so it is like two thick copper discs, spaced by lots of copper bars running between them close to the discs edges, so if you stood this thing up on one disc, you could put your pet squirrel in the centre of the cage.
Frank

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