# Motor "Speed" ratings, what does it mean?



## major (Apr 4, 2008)

> I copied this from a website selling an average industrial motor, as an example of what I'm asking:
> 
> Power Output: 75kW (100HP) at 50Hz
> Speed: 1480RPM at 50Hz
> ...


When what says that? Your example says "Speed: 1480RPM at 50Hz". That's likely an induction motor and that is the speed you'll realize when the motor is connected to the 50 Hz mains. 

If you used that motor motor in an auto-drivetrain with a 50 Hz supply you would be able to run only at that speed (1480 RPM) give or take a percent or two. That would indeed suck. So that's why you need a motor speed controller.


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## mbman88 (Feb 17, 2013)

major said:


> When what says that? Your example says "Speed: 1480RPM at 50Hz". That's likely an induction motor and that is the speed you'll realize when the motor is connected to the 50 Hz mains.


I will change this phrasing to make it more understandable. 




major said:


> If you used that motor motor in an auto-drivetrain with a 50 Hz supply you would be able to run only at that speed (1480 RPM) give or take a percent or two. That would indeed suck. So that's why you need a motor speed controller.


thank you, I think this answers my question. Just to confirm, would a Variable frequency drive be the proper way to control this motor for variable motor speeds?


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## major (Apr 4, 2008)

mbman88 said:


> I will change this phrasing to make it more understandable.


A good motor rating will mean what it says. If it is specifying a maximum RPM, it will say that. If it has a stated RPM next to a power rating, that is what it applies to. That is the rated power at that RPM. I don't know what you mean by "Speed" rating 




mbman88 said:


> thank you, I think this answers my question. Just to confirm, would a Variable frequency drive be the proper way to control this motor for variable motor speeds?


Actually, for vehicle propulsion motors, the operator needs to command motor torque via the motor controller. Such motor controllers are often called speed controllers. And for AC motors, motor speed is always related to frequency, so variable frequency drives are used (called inverters).

As far as getting stuck with horrible motor speeds for the auto-drivetrain, you've selected the wrong motor. There is application engineering which needs to be considered when designing the EV drive train. Get the proper motor for the job.


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