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DC Motors Vs. AC Motors: What's the Difference?

Mike Jeffries | May 17, 2021

The DC vs. AC motors debate has been going on for years. However, most people don't know a lot about this topic apart from the obvious fact that DC and AC motors differ in terms of how they are powered. Below is everything you need to know about these types of motors, what makes them unique compared to each other, and how you decide which one is the right choice for you.

What is a DC Motor?

DC motors primarily convert direct current electrical energy into mechanical rotational energy. You can also use the device in reverse by rotating a motor shaft to create DC electrical power (making the device function as a generator). 

However, note that DC motors include several types such as Brushless DC motors, Permanent magnet DC motors, and so much more.

What is an AC Motors?

These electromagnetic devices produce mechanical energy by converting alternating voltage and current. AC motors can be categorized as either Synchronous or Induction Motors. With induction motors, you either have a polyphase or a single phase. Synchronous motors are categorized as either Hysteresis or Reluctance motors.

What's the Difference Between AC and DC Motors?

The Magnetic Field

With AC motors, an alternating current is supplied to the stator coils forcing them to produce a rotating magnetic field (RMF). 

Consequently, the RMF generates an electromagnetic field (EMF) through Faraday's induction law. However, note that induction motors have a higher synchronous speed than the speed of the rotor.

With DC motors, a set of coils or a permanent magnet produce a non-rotating magnetic field. All the current gets supplied to the armature coils, thus leading to its rotation.

Speed Control

The speed of Dc motors is controlled by the current and voltage applied to the windings or armature coils. Adjusting the current flowing into the field coils will also dictate the speed of the device. Therefore, DC motors feature a proportional speed-current relationship.

The speed of AC motors is controlled by the alternating current frequency applied to their stator coils. Therefore, speed will increase when frequency increases and vice versa. The relationship between speed and current is directly proportional.


DC motors are crucial when you need speed control while AC motors are excellent when you need variable torque and high speed. However, note that the DC motors produce a stable and constant torque over different speed ranges compared to AC motors.

Ac motors experience the slip and induction current loss, thus suffer from efficiency problems. DC motors, on the other hand, are 30% more efficient because they use permanent magnets. Equally, note that DC motors don't need to create an electromagnet by consuming power.

Startup Mechanism

The Polyphase AC motors are self-starting and do not require any additional electronics to work effectively. DC motors, and Single-phase Ac motors, require some type of start-up mechanism that controls the conditions. For example, you have to control the initial ramp-up input voltage when stating a large DC motor to avoid burnout.

Input Power

A DC power source will supply a unidirectional current (no change in direction over time) to power a DC motor. AC motors, however, are powered with alternating voltage and current that changes in direction and amplitude once a wavelength is complete. The AC motors, therefore, can operate with a polyphase source or a single-phase source.

Let Professionals Handle Your Industrial Motor Needs

Learning the difference between DC and AC motors will help you pick out the best motor type for your company. However, hiring a professional ensures you keep your production ability optimized. At Mader Electric, we have a team of professionals with years of experience to keep your motor and control systems running effectively. 

Ensure you contact us today to learn more about how we can help you optimize production.

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