## AC Motors Speed

Discuss AC Induction motors, Reversible motors, Synchronous motors, Low-Speed Synchronous motors, Torque motors, Gearheads, Brake Packs and related Accessories here.
essenceindia
Posts: 34
Joined: Thu Nov 16, 2017 7:46 am

### AC Motors Speed

HI !!
One of our customer is looking for exactly 1400 / 1500 rpm with round shaft AC Motor, going through all our datasheet round shaft motors are mentioned 1250 rpm only. Please describe how to go ahead and convence the customer.

Whenever we calculated geared motor, the rotation speed is calculated by dividing by the reduction ratio based on the synchronous rotation speed of the motor (50 Hz: 1500 r / min, 60 Hz: 1800 r / min).

But direct motor, how to be calculate exactly working speed on the motor shaft for Round Shaft Motors ??

Thanking you & Best Regards,

om_tech_support_JS
Posts: 192
Joined: Tue May 10, 2016 4:48 pm

### Re: AC Motors Speed

Hi essenceindia,

In regards to your post, the synchronous speed of an AC Induction motor is calculated by the following equation:
Synchronous Speed Calculation.png (78.7 KiB) Viewed 3082 times
This means that a 60 Hz input would yield a synchronous speed of 1800 PRM and a 50 Hz input would yield a synchronous speed of 1500 RPM (As you have already described). Going further, the picture below is of the speed-torque characteristics of an AC Induction motor.
Speed-Torque Characteristics.png (100.53 KiB) Viewed 3082 times
From this graph, you can see that it is not possible for the motor to ever reach the synchronous speed, instead, the motor can only reach a maximum speed at point 5, which is the no load speed.

Since the speed of the motor will be dependent on the torque that the motor needs to operate at, we provide the synchronous speed and state that the actual running speed will be 2 ~ 20% less than this speed depending on the load. It is possible to run the AC Induction motor around the speed that they require as long as the load is held constant, however, any changes in the load could lead to the speed fluctuating.

For these reasons, if the 1400 / 1500 RPM is a key factor, then I would recommend looking at either an AC Speed control option, or Brushless DC speed control packages.

essenceindia
Posts: 34
Joined: Thu Nov 16, 2017 7:46 am

Hi,