Engines have existed in one form or another since ancient times, but the means of powering them has changed significantly from century to century. From the late 19th century on, electrically powered motors played an important role in industry, and the direct current (DC) motor was the first kind of electric motor to be built.
Though DC motors have existed for a long time, picking the right one for your end-use application can prove challenging. This guide will describe the components of a DC motor, the most popular DC motor types, and how you should go about selecting one.
Components of DC Motors
At their heart, DC motors are simple to conceptualize. These rotary motors run off direct-current electricity, which they transform into mechanical energy by using magnetism. DC motors have two main parts. The first is the stator, a stationary part of the motor which contains a number of magnets. The second is the rotor, which turns and has field windings (i.e., insulated wiring) inside it. (These windings are sometimes called an armature.) The magnetic force generated in the stator reacts with the magnetic force in the rotor to create turning power, which causes the motor to function in its expected way.
While the stator and the rotor are the most important parts of a DC motor, virtually all DC motors contain the following additional elements. We have already alluded to the windings that help generate magnetic force, and a commutator is a rotary switch with copper segments. Bearings provide structural support for the rotor, and the entirety of the device is contained by a case that has insulation.
Popular Types of DC Motors
Despite the fact that DC motors are fairly simple, you will find a great variety of these devices available to purchase. Following are some of the more common types of DC motors, which include:
Brushed DC Motors
This common kind of DC motor uses brushes of carbon or graphite to conduct magnetic force from the stator to the rotor. They’re relatively inexpensive and appear in a wide variety of end-use applications, including everything from children’s toys to health-care equipment to automobiles. The downside of brushed motors lies in the fact that the brushes wear down, necessitating more frequent servicing.
Brushless DC Motors
These motors do away with brushes and include permanent magnets in the rotor, which does away with much of the maintenance brushed motors require. They also feature a constant RPM and tend to be quieter. However, they need special technology to control their speed and cannot handle high loads upon starting. They also require a controller that converts direct current to alternating current.
Permanent Magnet DC Motors
While these motors are somewhat similar to brushless DC motors, they also have significant differences. They don’t require a controller and can operate in harsher environments. They also tend to only work best in lower horsepower uses.
Series DC Motors
The distinctive aspect of these motors is how the field windings and the armature share the same power source. They feature low resistance and start with very high torque, but they cannot regulate their speed, which may lead to damage if the motor is started without a load.
Shunt DC Motors
By connecting the motor’s field parallel to the windings of its armature, you’ll end up with a shunt motor, which can regulate its speed well. However, it has a lower starting torque than other options.
Compound DC Motors
A hybrid of series and shunt motors, compound motors struggle with variable speed, but excel when it comes to high starting torque and constant speed operation.
Other popular kinds of DC motors include stepper motors (which can function for a particular period of time, called a step) and washdown motors (which can function in damp environments).
DC Motors vs AC Motors
The differences between AC motors and DC motors begin with the types of power supplied to them, a fact that’s evident in their very names. Indeed, motors that use alternating current have become popular due to lower maintenance requirements and their generally constant speeds. However, direct-current motors excel in certain specific applications. If you need a motor that will function well under the following variables, then you’ll want to select a DC motor:
- You want to control the motor’s speed by changing the supply voltage.
- You need a mobile motor that will function off of battery power.
- You need a high-speed motor.
- You need to start or stop or reverse the motor quickly.
- You need a motor with a high starting torque.
- You need a motor that’s easy to control.
- You need an inexpensive motor that functions reliably (e.g., a brushed DC motor).
How to Properly Size a DC Motor
Motor sizing is a complex task that depends heavily on a number of end-use factors, such as how an employed actuator mechanism (e.g., pulley, rack and pinion) affects torque, the inertia generated by a specifically shaped load (e.g., solid cylinder, hollow cylinder, solid rectangle), the maximum allowed load inertia permitted by the motor’s gearhead, and more. Dr. Alaa Khamis of General Motors has published a useful guide on motor-sizing calculations, but in general, you can start by calculating the following as related to your end-use application:
- Load torque
- Load inertia
Once you have these in hand, you should also have a general idea of what kind of motor will work well in your specific scenario.
What to Look for When Buying a DC Motor
While factors such a motor’s voltage requirements, speed, RPMs, and torque are important, purchasers need to consider more than merely a device’s raw technical specifications, though. They should think about other practical issues, such as:
Cost of Operation
While the IEC 60034-2-1:2014 standard for energy efficiency in motors may constrain certain buying decisions, such environmental regulations only apply to AC motors. However, that doesn’t mean you want to ignore a DC motor’s efficiency. Selecting an inefficient device may greatly increase your costs in the long run.
The actual space into which you want to install a motor has multiple implications when selecting a device. For instance, will the DC motor physically fit into the area designated for it? Is there enough ventilation for the motor? Will the motor meet local ordinances relating to sound restrictions? What will the temperature be? Will the operating context be particularly dirty or wet? Will the motor come into contact with contaminants?
In some cases, performing regular maintenance on a DC motor poses little downside. However, in other scenarios, such a requirement might prove burdensome.
Applications and Industries
DC motors are a mature, established technology, and as such, they find uses in many different industries. You will find them in fields such as heavy industry, manufacturing, and consumer-goods production. Other types of businesses that use them include:
- Automobile Manufacturing
- Paper Production
- Steel Production
- Electrical Utilities
- Mass Transit
In these professional contexts, DC motors have multiple end-use applications, some of which include:
- Household Appliances
- Centrifugal Pumps
- Air Compressors
- Maritime Engines
- Disc Drives
- Conveyor Belts
- Rolling Mills
- Boring Mills
- Medical Equipment (e.g., electric wheelchairs)
- Weaving and Sewing Machines
- Automotive Starters
- Trolley Cars
- Computer Equipment
DC motors don’t typically require many accessories to function properly. Selecting the proper motor type usually solves any potential issues. However, there are some common accessories that may help guarantee proper function, such as:
- Replacement Brushes
- Stabilizing Bases
- Electronic Motor Controllers
- Motor Mounts
- Power Boards
- Cushioning Rubber End Caps
Tips for Finding and Buying a DC Motor
When you’re looking for a DC motor, you want to use an established source. Surplus Record has decades of experience in placing interested buyers with trusted sellers. Additionally, searching our website is easy! Simply visit our Electric Motor Search page and narrow down your search by power type, horsepower range, RPM range, voltage range, frame type, manufacturer, and motor condition.
Surplus Record provides more than just classified listings, too. We work with specialty dealers who can help you find the perfect DC motor for your applications. Search for area dealers near you or search dealers by name.