Are Servo Motors AC or DC? | The Edge Cutter

Servo motor is a kind of electromechanical equipment that produces high speed to any machinery by creating faster spin with the help of supplied power as well as voltage. It helps the particular part of any machine to rotate in higher velocity and work as closed loop order. In some machineries servo motors work as speed controllers. Servo motors are also used in CNC machines, computers, radar systems,  tracking systems, robotics, automated industrialized systems and so many more machines.

There is a common query if servo motors are AC or DC! Servo motors can be of both types; like AC  and DC. Though both the servo motors work in the same way, they are different from each other because of their source of power supply. In this article we will discuss how AC and DC servo motors are used in different machines along with a few basic differences between the duo. So, keep moving forward to explore them elaborately. 

Types of servo motors

There are two types of Servo motors: AC servo motor and DC servo motor. Servo motors can be evaluated according to three basic considerations. Firstly, power source for their workability, that means if they are powered by AC or DC current. Secondly, methods of communication like if they are brushed or brushless. Lastly, servo motors’ revolving fields, whether the impellers’ twirling is synchronized or not. 

Here is a comparative brief cum quick overview table of both AC and DC servo motors:

FactorsAC servo motors DC servo motors 
Stability Efficiently utilising and less stability issue Frequent malfunctions and stability problems 
Sound Pollution Produce no radio frequency noise Produce loud radio frequency noise
Application Smooth and stable operating system Sound polluting operation 
Dimension and weight Condensed size and lightweight, portable Larger dimension with heavily loaded
Velocity and rotation Flexible and strongly adaptive to working in high velocity and torque conditions Capable to work in limited torque and velocity 
Power production Lesser power output Produce high energy 
Servicing and maintenance Less renovation required Demands regular maintenance 

Now let’s focus deeper into each of the above mentioned servo motor types. 

AC Servo Motors 

AC servo motors are run by the prevalence of the voltage of the power applied and the count of magnetic poles on the motor. AC servo  motors have two different varieties. Such as Synchronous and Asynchronous. They are divided as per their speed to the rotation field. A synchronous AC servo motor’s rotor revolves at the same frequency which is equal to the static part’s magnetic field’s velocity. This type of speed frequency is known as synchronous speed. Synchronous AC servo motors have dynamic performance capacity and are often used in various servo systems.

Asynchronous AC servo motors as well as the induction motors provide slower rotating speed than the static part of the magnetic field of any machine. Induction motors are supported by different frequency control variables to achieve speed controlling capacity. But they are not responsive to the procedure. So they are not really considered as servo motors.

Most of the industrial companies use AC servo motors in their machines because of their excellent speed controller capacities, closed-loop control system, encoding accuracy, creating more torque according to weight, elimination of radio frequency noise due to rotation etc. Notably, Synchronous AC motors are more applicable servo motors than Asynchronous AC motors. 

DC Servo Motors 

A DC motor’s torque is equal to the dispension of the voltage. That means if the voltage is high the speed frequency will be high too. DC servo motors are also divided by two subsections; Brushed DC motors and Brushless DC motors. This subdivision has been made whether the DC motors are commutated mechanically l, like with a brush and a communicator, or if their method of commutation is electronical. 

Though both the DC motors are used in servomechanism systems, brushed DC motors are not that much applicable for using as servo motors. Because they provide slower spinning speed with only one magnetic field and there are chances of frequent wear and tear of the same. Moreover they are required to be maintained periodically and their brushes need to be replaced regularly. 

Brushless DC motors are perfectly made for any kind of servo application. They are highly efficient and dynamic as well as reliable in their service. As BLDCs have no brush to be collided with anything during rotation. So there is zero possibility of loss of energy due to collision.  They need not to be maintained so frequently and they have the capacity of running 50 percent longer on batteries than BDCs.


DC servo motors are mainly used in computers as prime movers, machines with numeric controlling systems. They are also used in those machines that require to be started and stopped quickly. DC servo motors include appliances like cranes, vacuum cleaners, hair dryers, lifts, winching systems etc.And, that’s all folks! Hope the above mentioned discussion will be helpful for you. 

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