# Single phase induction motor Torque under increased frequency and Same/Constant current.

#### Stoyan.Nikolov.2Induction

Joined Nov 26, 2023
14
Consider Single phase induction motor.

What will be torque of induction motor, if we increase supply frequency 10 times, if the motor uses same supply current.

Let's say Torque (Supply frequency 50 Hz, Supply current 10 Amperes ) = N

What is Torque (Supply frequency 500 Hz, Supply current 10 Amps) = ?

Will it be 10*N ?
------------------------------------------
Also what will be the Output Power?

Let's say Power (Supply frequency 50 Hz, Supply current 10 Amperes ) = N

What is Power(Supply frequency 500 Hz, Supply current 10 Amps) = ?
Thank you.

#### crutschow

Joined Mar 14, 2008
34,392
Consider the power.
Assuming the motor operates normally at 10X frequency, giving 10 times the output RPM, the output torque will be 1/10th for the same current, since torque times RPM determines the power output, and the input power hasn't changed.

#### Stoyan.Nikolov.2Induction

Joined Nov 26, 2023
14
Consider the power.
Assuming the motor operates normally at 10X frequency, giving 10 times the output RPM, the output torque will be 1/10th for the same current, since torque times RPM determines the power output, and the input power hasn't changed.
The motor uses same current for both frequencies.

Joined Jul 18, 2013
28,669
The motor uses same current for both frequencies.
Not with the same load, surely?

#### Stoyan.Nikolov.2Induction

Joined Nov 26, 2023
14
Not with the same load, surely?
What will be the resultant torque. Same current from source, 10 Times greater frequency.

Joined Jul 18, 2013
28,669
It would be expected that the resultant Torque will decrease with increase in frequency.
How do you maintain the same current for both ?

#### Stoyan.Nikolov.2Induction

Joined Nov 26, 2023
14
It would be expected that the resultant Torque will decrease with increase in frequency.
How do you maintain the same current for both ?

#### LowQCab

Joined Nov 6, 2012
4,053
Smoke will be the result.
.
.
.

#### crutschow

Joined Mar 14, 2008
34,392
That's now how it works.
The motor current is determined by the load for a given frequency.

#### Stoyan.Nikolov.2Induction

Joined Nov 26, 2023
14
And I cant regulate it by adjusting voltage ?

#### crutschow

Joined Mar 14, 2008
34,392
And I cant regulate it by adjusting voltage ?
In a way.
For a given load (power) the current will go up as the voltage goes down to maintain a constant input power.

Last edited:

#### Stoyan.Nikolov.2Induction

Joined Nov 26, 2023
14
So if I increase input voltage I increase Input current and Torque too.

If I increase input Frequency and manage to supply same current I Increase Torque too.

Last edited:

#### LowQCab

Joined Nov 6, 2012
4,053
Watts of Electricity can be converted directly to Horsepower or Kilowatts, and vice-versa.

Torque (Pounds/Feet) X RPM / 5252 = Horsepower

735.5 Watts = 1-Horsepower = 735.5 Watts.

If You put more Watts of Electrical-Power into the Motor,
the Motor will have to dissipate MORE-HEAT !!!!
At some point the Motor will fail because of excessive HEAT.

The Motor is rated at a Horsepower-Level, or Wattage-Level,
( either of which are effectively the same thing ),
that will not exceed the amount of Heat that the Motor can reliably withstand.

If You need high-RPM capability,
use a DC-Motor, or a "Universal-Motor",
NOT a Synchronous-Motor.
.
.
.

#### schmitt trigger

Joined Jul 12, 2010
889
Take this from someone who actually designed and built electrical motors as a real job:

AC INDUCTION motors (not the AC SYNCHRONOUS) are constant V/f ratio devices. If you increase the frequency without increasing the voltage, the rotor slip will increase and the torque will drop like a rock.
You would have to increase the input voltage 10 times, meaning that the applied voltage would be 2.3 kilovolts. The rotor speed would increase roughly 10X
Thus, in addition to the steel core overheating, the bearings overheating, the 10X centrifugal forces pulling the rotor apart, you would also have to deal with the insulation arcing all over the place.

I don’t think your interest is purely academic, as you have stated somewhere else. What exactly are you planning to do?