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The Constant Speed Motor The complete Guide

There are several different types of constant speed motors. When choosing from a large selection of products, keep in mind the application, required functions, output, and so on. The process of selecting a motor and gearhead should begin with a thorough examination of the motor’s specifications to ensure that the motor you choose meets the application’s requirements.  What you need to begin your selection is some factual and useful information the motors. The constant speed electric motor combines an induction motor with a power on activated type clutch and brake. It’s perfect for frequent start-and-stop operations. Suitable for situations where the motor is run at synchronous speed independent of load torque and the motor is started, stopped, and reversed frequently.

Different Types of Industrial Motors

There are over three dozen different types of motors utilized in industrial applications, despite the fact that there are only two basic motor classifications: ac and dc.

While there are many different motor types, there is a lot of overlap in industrial applications, thus the market has pushed for motor selection to be simplified. In most applications, this has reduced the motor options. Brushless and brush dc motors, ac squirrel cage and wound rotor motors, servo and stepper motors are the six most popular motor types that meet the great majority of applications. The other types of motors are only utilized in specialized applications, but these motors are suitable for the great majority of applications.

Constant Speed Electric Motor Diagram
Constant Speed Electric Motor Diagram

What are Constant Speed Motors?

Constant Speed Motors refer to standard electric motors which have normal operating speed that is theoretically or practically constant. An example is synchronous motors; low slip induction motors or conventional parallel winding DC motors.

In this case, you can call an induction motor, which is defined as a constant speed motor. The rotor flux rate lags slightly behind the stator flux and there is a relative velocity between the stator and the rotor. The difference in engine speed changes slightly with increasing engine load. In a vacuum, this is called sliding speed. There is very little slip at idle and the torque generated by the engine matches idle and friction losses. Consequently, at idle speed, the motor rotates at almost synchronous speed (Ns = 120f / P).

📌When the load increases, the motor tries to transfer the load to the mechanical load, and in this process the motor speed decreases. Decreasing the motor speed causes slip to increase and the motor draws a large current from the rotor to transmit torque, which tends to return the motor speed to its original speed.

The slip of the induction motor ranges from 3% to 5% of the synchronous speed. As the inductive load increases, the slip decreases within the specified slip range. Therefore, an induction motor can be called a constant speed motor.

Constant Speed Electric Motor Image
Constant Speed Electric Motor

Constant-Speed Application, a Constant-Speed Motor

In a constant-speed application, a motor typically runs at a constant speed, with little or no regard for acceleration and deceleration ramps. Across-the-line on/off control is commonly used in this sort of application. A branch circuit fusing with a contactor, an overload industrial motor starter, and a manual motor controller or soft starter are common components of control circuits.

📌 For constant speed applications, both ac and dc motors are acceptable. DC motors have a large installed base and offer full torque at zero speed. AC motors are also a suitable alternative due of their high-power factor and low maintenance requirements.

What Is the Difference Between Constant Speed and Double Speed Tools?

  • One main difference is the gearbox design. Constant speed tools provide maximum speed and power, but dual speed tools can be configured for two modes: fast and slow.
  • Working with a two-speed tool is more efficient. On the contrary, a tool with a constant speed provides a lot of power and is very convenient for projects that require a lot of effort.
  • A double-speed tool can be used for various types of work, but a constant-speed device has been designed for a special purpose. For example, a double-speed drill is used for drilling, impact drilling and wrapping. But an ordinary drill is only suitable for drilling operations.
  • The versatility of single-speed tools is much less than that of two-speed tools, even if the power is the same.


What do you call a constant-speed motor if you don’t know what it’s called?
A shunt motor is a direct current motor having two parallel windings that have the same voltage across them. Induced voltage is proportional to speed in a shunt motor, and torque is proportional to armature current.

Which DC motor has a constant rotational speed?
DC shunt motor always maintains a constant speed.

Conclusion 📜

Standard electric motors with a theoretically or practically constant typical operating speed are known as constant speed motors. Synchronous motors, low slip induction motors, and ordinary parallel winding DC motors are examples.


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Anton Abramov

I am a 29-year-old Russian boy living in Tajikistan. I studied IT at university of Moscow. I have been working with my father's tools since I was a teenager. I fix tools, repair them and I always try to find out how they work. So, I would call myself a geek in power tools. On my journey to becoming a pro, I will try to share the knowledge I've gained through years of experience with you.

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