What is a DC motor? - features and mechanisms

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30 Mar. 2020

This page focuses on DC motors, which are electric motors driven by direct current (DC). Two features that distinguish DC motors from AC motors and stepper motors are their high starting torque and ability to run at high speed.

Generally, an electric motor is a machine that converts electrical energy into mechanical energy, and uses the electricity generated to produce rotational motion and thereby to do work. DC motors are used in a wide variety of different devices and appliances that play a part in our lives.

Behavior of a brushed DC motor

What are DC motors used for?

It is no exaggeration to say that DC motors are being used all around us in our daily lives. They are used in many different ways and take on many different forms. Examples from your home might include air conditioners, refrigerators, and water heaters. At work, DC motors will likely be used in your office's audiovisual projectors or inside the ATMs used by banks. Use of the motors extends well beyond these examples, encompassing home appliances, especially air ventilation systems, and also cars and medical devices.

DC motors are produced in huge volumes and, as a source of noise and a means of achieving energy efficiency, they play a very important role both in determining living conditions and in the global environment.

What distinguishes a DC motor from other types of electric motors?

Types of electric motors

The many different types of electronic motors can be broadly grouped into the following three categories based on their internal design and how they work.

  • DC motors (powered by direct current)
  • AC motors (powered by alternating current)
  • Stepping motors (motors that rotate one step at a time in response to electrical pulses)

Two features that distinguish DC motors from the other two types are their high starting torque and ability to run at high speed.

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DC motor with brush Brushless DC motor AC motor Stepper motor
Efficiency Superior Inferior
starting torque Superior Inferior Inferior
Rotational speed Higher depending on setting 3,600rpm or less
(bipolar, 60Hz)

2,000rpm or less
(depending on control method)

Possibility of Missing steps or slipperiness No slipperiness Missing steps
Long lifetime Depending on lifetime of brush Yes Yes Yes
Need driver circuit No Yes No Yes
Control algorithm applied Normally closed loop Normally open loop
Positioning control Possible on servo motor Possible on servo motor Possible
Constant speed control Superior Best Inferior Superior

DC motors can be divided into brushed and brushless DC motors

DC motors are divided into two categories depending upon whether or not they use brushes and commutators.

Brushed DC motors work by direct connection to a source of DC electric power. Brushless DC motors, in contrast, require a drive circuit and work by supplying the appropriate current through static windings based on the detected orientation of the magnetic poles of the rotor.

Cutaway schematic diagram of brushed DC motor

Cutaway schematic diagram of brushless DC motor

Respective features of brushed and brushless DC motors

Brushed DC motors

Brushed DC motors can be broadly divided into the following two types depending on whether they use permanent or electro-magnets.

Permanent magnet brushed DC motor
This is the most common form of electric motor used worldwide and includes the motors used in models and in the auxiliary motors of automobiles. They are further divided into slotted, slotless, and coreless motors depending on the configuration of the armature.
Electromagnet brushed DC motor
These types of motors use electromagnets to generate magnetic flux. They are further divided into distributed-winding, series-wound, and separately-excited motors depending on how the electrical connection between the field winding and armature winding is configured. This configuration is used for motors with medium to high output.

Brushless DC motors

Because their windings remain static, brushless DC motors do not require brushes and a commutator. They are divided into the following types based on how the permanent magnets are attached to the rotor.

Surface permanent magnet (SPM)
The permanent magnets are attached to the outer circumference of the rotor.
Interior permanent magnet (IPM)
The permanent magnets are embedded in the interior of the rotor.

Advantages and disadvantages of DC motors

Brushed DC motors are currently the most commonly used because they are easy to miniaturize and provide good control of rotation together with high efficiency.
Brushless DC motors, on the other hand, benefit from long life, ease of maintenance, and low noise because they do not have the brushes and commutators, which are the downsides of brushed DC motors.

Features of brushed DC motors

  • No need for a drive circuit when running at constant speed
  • High-efficiency design
  • Able to operate at high speeds
  • High startup torque
  • Responsive and easy to use as speed and torque can be controlled by voltage
  • Motor life is shortened by the need for brushes and a commutator, which are subject to wear.
  • The brushes generate both electrical and acoustic noise

Features of brushless DC motors

  • Lack of brushes means long motor life
  • High-efficiency design
  • Stability of speed control
  • Able to operate at high speeds
  • High startup torque
  • A drive circuit is required

Overcoming your problems with brushless DC motors

Of DC motors, ASPINA suppplies brushless DC motors. We do not only develop standalone brushless DC motors, but also system products that incorporate drive and control systems as well as mechanical design. These are backed by comprehensive support that extends from prototyping to commercial production and after-sales service.
ASPINA can offer solutions that are tailored to suit the functions and performance demanded by a diverse range of industries, applications, and customer products, as well as your particular production arrangements.

ASPINA supports not only customers who already know their requirements or specifications, but also those who are facing problems at early stages of development.Do you struggle with the following concerns?

Motor selection
  • Don't have detailed specifications or design drawings yet, but need advice on motors?
  • Don't have anyone in-house with expertise in motors and can't identify what sort of motor will work best for your new product?
Motor and associated component development
  • Want to focus your resources on core technology, and outsource drive systems and motor development?
  • Want to save the time and effort of redesigning existing mechanical components when replacing your motor?
Unique requirement
  • Need a custom motor for your product, but been declined from your usual vendor?
  • Can't find a motor that gives you the control you require, and about to give up hope?

Seeking answers to these problems? Contact ASPINA, we’re here to help.

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