Factors to Consider When Choosing an Electric Motor for Your Facility
Maintaining industrial and commercial machinery requires many tasks. One of the most significant responsibilities is inspecting, maintaining and repairing electrical motors. You need to ensure facility tools meet safety standards and efficiency requirements, and choosing a suitable electric motor is a key part of that job.
How to Choose an Electric Motor
Electric motors power numerous industrial and commercial applications and support many functions, like powering machine compressors, pumps and tools.
However, not all electric motors are equal, and some suit specific applications better than others. Considering factors like speed, torque, duty cycle, load compatibility and maintenance requirements can help you select a compatible electric motor for your industrial facility.
Torque
Suitable torque is necessary for driving electric motor startup and acceleration speeds. Applications require varying amounts of force to start up and accelerate load to a specific rate in a set time. You’ll need to consider a piece of equipment’s torque requirements when choosing an electric motor to ensure it can operate without excessive strain.
Speed
Your electric motor’s output speed must be compatible with your needs. Some electric motors suit high-speed applications, while others are better for moderate- to low-speed processes. Your application might also require adjustable controls that accommodate specific increments. Understanding different motor designs and output capabilities is vital for selecting a suitable range for your applications:
- Industrial AC horizontal electric motors: Horizontal AC motors are widely used in applications such as pumps, compressors, fans, conveyors and other machines that require continuous and reliable mechanical power. These motors offer high efficiency, durability and the ability to operate under demanding conditions.
- Industrial DC electric motors: DC electric motors are commonly used in applications that require precise control of speed and torque, such as robotics, CNC machines and conveyor systems. Advantages of these motors include ample starting torque, adjustable speed and relatively simple control mechanisms.
- Industrial AC vertical electric motors: AC vertical electric motors are designed to handle the challenges of vertical applications, such as the weight of the rotating parts and the thrust load from the pump or compressor. They are built with robust construction and specialized features to ensure reliable and efficient operation in these demanding environments.
Power Source
Do you need an AC or DC motor? Selecting a suitable power source is vital for running your equipment effectively. DC motors allow for fine speed control since their rpm output is directly affected by the amount of voltage supplied. AC motors require a variable frequency drive for speed variation but offer greater efficiency. An AC motor tends to excel in low- to medium-speed operations, while DC performs better when higher speeds are needed.
Speed Settings
Does the motor offer different speed ranges and control settings? Some applications require a definite operating speed, while others need adjustable rates. You can add a controller or drive to your DC or AC electric motor to manage torque and rotation. A controller can also regulate different application speeds, weights and loads.
Operating Lifetime
The motor’s operating lifetime determines the life span of a product or tool. Consider how long you’ll need the motor to last and how much time and money you plan to put into maintaining it. Brushless DC and stepper motors have fewer wear components and tend to last longer, while brushed DC motors deteriorate more quickly.
Duty Cycle
The duty cycle determines how long the motor can run over production cycles. You might run applications continuously or over short periods. A longer run time will require a motor with a higher duty cycle to ensure you don’t lose power. You can use a smaller motor if you only need it intermittently and it will have enough rest time to return to ambient temperature.
The environmental temperature will affect a motor’s duty cycle, as the objective behind limiting run time is preventing overheating and any resulting damage.
Enclosure Ranking
The enclosure ranking depends on the conditions a motor must operate under. Consider the environment surrounding the installation — will the motor be exposed to moisture, dirt, debris or extreme heat? Neglecting to provide proper protection during installation is one of the most common causes of motor failure.
You’ll need suitable protection for your motor depending on your working conditions. For example, food and beverage industries might need stainless steel castings to protect machinery motors from spills, corrosion and wear.
Voltage
Some electric motors can run on batteries or a power outlet. Depending on the facility, you’ll need to decide if you’ll connect a motor to the power grid, inverter or batteries. The voltage must be compatible with your motor if you use a wall socket or outlet. Smaller tools and lower power applications can use standard voltage, but you will likely need to draw more power for industrial motors.
Performance Temperatures
Depending on your working conditions, a motor can require climate protection. Consider the temperature of the facility. Is it a hot or cold environment? Understanding the climate will help you select a motor with suitable materials or coverings.
Control
Some applications require both backward and forward rotation. Some motors do not have multiple reverse or rotation capabilities, so be sure to choose a motor that can do everything your tasks require.
Capacity and Size
Electric motor capacity and size will impact operational efficiency. An electric motor must offer sufficient torque for your application’s load without generating more heat than the insulation present can handle.
A key factor in selecting motor size is whether you will be installing it permanently or in a system you plan to move often. You can get a bigger motor for equipment that will remain in one place, like a large lathe in an industrial building. Anything you need to transport often will call for careful consideration.
Noise levels
Whether noise is a concern will depend on where you’re using the motor. You might select a model geared for noise reduction if the installation will be in a public area like a hospital.
Maintenance
Motors have different maintenance requirements. Consider the motor type and if you can maintain and repair it yourself or need professional services. DC motors tend to be more challenging to maintain and require expert knowledge.
Feedback Components
Having a way to collect data on motor performance can enhance your applications. With encoders or sensors, you can get feedback on how well the motor works and adjust speed and other settings for better performance. Data components offer diagnostic capabilities to indicate wear or damage so you can schedule maintenance, preventing breakdowns and downtime.
Operating Costs
A motor’s operating costs depend on its life span, maintenance requirements and initial price. You’ll need to decide which model will offer the best value for your money or return on investment. Weighing potential costs is necessary before selecting an electric motor for your commercial facility.
Rely on Industrial Electrical Company for Comprehensive Electric Motor Services
Deciding on an electric motor for your industrial or commercial facility requires you to look at many complex factors. If you want to ensure you select the best model based on your unique circumstances, it’s best to consult a professional. Industrial Electrical Company specializes in various electric motor services, including installations, preventive maintenance and repairs.
Our certified technicians are experts in their craft. We’re also committed to delivering exceptional customer service, and we’ll answer your calls 24 hours a day. Whether you want us to evaluate trouble signs with an existing motor or assess your requirements and help you choose a new model, our team will make sure you have everything you need.
Contact us to learn more about our electric motor services.
Which type of electric motor do you size for your conveyor, XYZ table, or robot? Before you select one, you must understand the characteristics of each type of motor in the market.
Types of Electric Motors
There are two obvious types of electric motors as determined by input voltage: AC (Alternating Current) or DC (Direct Current).
While AC motors use alternating current to power a series of wound coils, DC motors use direct current to power either carbon brushes or electrical commutation. DC motors are generally more efficient and compact than AC motors.
It's not only important to understand the differences between the characteristics of AC and DC motors but also the specific types within these categories.
Remember that certain manufacturers have the ability to offer both motors and drivers. Even if the motor is DC, its driver can house an internal power supply, so AC input drivers can easily run DC motors with an AC power supply.
Now let's dig deeper into AC and DC motors.
Ideal for Constant Speed: AC Motors
AC motors can be separated into four main categories: shaded-pole, split-phase, capacitor-start, capacitor-start/capacitor-run, and permanent split capacitor. Since Oriental Motor only manufactures permanent split capacitor type AC motors from 1/2 HP down to 1/750 HP, we will generally cover this segment in more detail.
Each type of PSC motor is similar in structure. There are wound coils in the stator and a squirrel cage rotor is used for rotation. Capacitors are required for single-phase motors to generate a polyphase power supply. These motors are very easy to control and require no driver or controller to operate. Minor differences change the characteristics of the basic AC induction motor to suit different performance needs, such as various types of brakes.
Induction Motors / Asynchronous Motors
Induction motors are the most common and are rated for continuous duty operation for a wide range of output power from a fraction to thousands of horsepower. They're considered "asynchronous" motors due to the existence of a lag, or slip, between the rotating magnetic field produced by the stator and its rotor. The reason why they're called "induction" motors is that they operate by inducing a current onto the rotor. Since there's no friction besides the ball bearings, they offer an overrun of approximately 30 revolutions after power is removed (before gearing).
The below image describes the design and construction of an induction motor.
① Flange Bracket
Die-cast aluminum bracket with a machined finish, press-fitted into the motor case
② Stator
Comprised of a stator core made from electromagnetic steel plates, a polyester-coated copper coil and insulation film
③ Motor case
Die-cast aluminum with a machined finish inside
④ Rotor
Electromagnetic steel plates with die-cast aluminum
⑤ Output shaft
Available in round shaft type and pinion shaft type. The metal used in the shaft is S45C. Round shaft type has a shaft flat (output power of 25 W 1/30 HP or more), while pinion shaft type undergoes precision gear finishing.
⑥ Ball bearing
Oriental Motor only uses ball bearings.
⑦ Lead wires
Lead wires with heat-resistant polyethylene coating
⑧ Painting
Baked finish of acrylic resin or melamine resin
How Do They Work?
When the motor is powered, it generates a rotating magnetic field in the wound stator. By Faraday's Law of electromagnetic induction, current is induced onto the rotor, and the magnetic field created by the induced current interacts with the rotating magnetic field to produce rotation. Its characteristics can be further understood by Lenz's Law and Fleming's Left Hand and Right Hand Rules. However, overrun, depending on load inertia, can be up to 30 revs. For anyone who wants to know more, here's a blog post for more background and technical information on AC induction motors.
Speed-torque curve depicts expected motor performance
A motor's performance is plotted on a speed-torque curve. An AC induction motor will start from zero speed at torque "Ts", then gradually accelerate its speed past the unstable region, and settle on "P" in the stable region where the load and torque are balanced. Any changes to its load will cause the position of "P" to move along the curve, and the motor will stall if it operates in the unstable region. Each motor has its own speed torque curve and a "rated torque" specification.
Induction motors are robust and can be used for a variety of general-purpose applications where continuous duty is necessary, and stop accuracy isn't critical. Single-phase motors are offered for fixed speed requirements. Variable speed requirements can be met by combining a three-phase induction motor with a VFD (variable frequency drive) or a single-phase motor with a TRIAC controller. Some manufacturers also offer wateright, dust-proof motors by enclosing an induction motor in a sealed case.
Reversible Motors
Reversible motors, by definition, can reverse on the fly and are ideal for start/stop operation. A reversible motor is similar to an induction motor but with a friction brake and more balanced windings. Due to a friction brake mechanism, its overrun is significantly reduced after power is removed. The motor winding is also more balanced to increase its starting torque for start/stop operation.
Due to the additional heat generated from reversible motors, their recommended duty cycle is only 30 minutes or 50%. An example of a reversible motor application is an indexing conveyor that isn't too demanding on throughput or stop accuracy.
How Do They Work?
A friction brake mechanism is installed at the rear of a reversible motor. The coil spring applies constant pressure to allow the brake shoe to slide toward the brake plate.
When the motor stops, the friction from the brake reduces the motor overrun from ~30 revs to ~6 revs.
The brake force produced by the brake mechanism of an Oriental Motor's reversible motor is approximately 10% of the motor's output torque.
The graph shows the difference between speed-torque curves of an induction motor vs a reversible motor. A reversible motor has highter starting torque characteristics than an induction motor.
Electromagnetic Brake Motors
Electromagnetic brake motors combine either a three-phase induction motor or a single-phase reversible motor with a built-in power-off-activated electromagnetic brake. Compared to reversible motors, these motors offer an overrun of just 2~3 revolutions (before gearing) and can be used up to 50 times a minute. These motors are designed to hold their rated load during a vertical operation, or just to lock the motor in place when power is removed.
The brake mechanism inside an electromagnetic brake motor is more advanced than the reversible motor. Instead of a brake shoe and a coil spring that constantly applies pressure, the electromagnetic brake is engaged and disengaged by an electromagnet and spring mechanism.
How Do They Work?
This is a power-off-activated type of brake, which means the brake engages and stops the motor when power is removed from its lead wires. When voltage is applied to the magnet coil during normal operation, it becomes an electromagnet and attracts the armature, with the brake lining, against the force of the spring and away from the brake hub, thereby releasing the brake and allowing the motor shaft to run freely. When no voltage is applied, the spring presses the armature onto the brake hub and holds the motor's shaft in place, thereby actuating the brake.
Electromagnetic brake motors are used in vertical applications where the load must be held, or in applications where the load must be locked into position when the power is removed.
Torque Motors
Torque motors are designed to provide high starting torque and sloping characteristics (torque is highest at zero speed and decreases steadily with increasing speed), along with operating over a wide speed range. Due to their ability to alter torque output based on input voltage, they provide stable operation under a locked rotor or stall condition, such as a winding/tensioning application.
How Do They Work?
A torque motor can vary its torque and speed according to the load torque.
Easy torque adjustment for tensioning
A voltage controller, such as the TMP-1, can be used to vary voltage to a torque motor to control its torque. Just like a speed controller, a voltage can be set using a potentiometer or external DC voltage.
Synchronous Motors
Synchronous motors are called "synchronous" because they use a special rotor to synchronize their speed with the input power frequency. For a 4-pole synchronous motor running at 60 Hz power, it will rotate at 1800 RPM (AKA "synchronous speed"). My earliest memory of a synchronous motor application was someone using it to drive the clock hands of a tower clock.
How Do They Work?
This type of motor offers a bit more responsiveness and precision on the speed. Its synchronous speed is determined by how many poles the motor has and the frequency of input voltage.
Another type of synchronous motor called the low-speed synchronous motor provides highly precise speed regulation, low-speed rotation, and quick bi-directional rotation. These motors actually use the rotor and stator laminations from a stepper motor design but are driven by AC power supply. Therefore, they're more responsive, but the higher number of poles also decreases the synchronous speed to 72 RPM at 60 Hz. Low-speed synchronous motors can stop within 0.025 seconds at 60 Hz if operated within the permissible load inertia.
The basic construction of low-speed synchronous motors is the same as that of stepper motors. Since they can be driven by an AC power supply and offer superb starting and stopping characteristics, they are sometimes called "AC stepper motors".
Ideal for Speed Control: DC Brushed and Brushless Motors
DC motors are generally much smaller than AC motors and use direct current to power the carbon brushes and commutator, or electrically commutate the windings with a driver. DC motors are about 30% more efficient than AC motors since they do not have to induce current to create magnetic fields. Instead, they use permanent magnets in the rotor. Oriental Motor's DC motors are generally fractional horsepower; up to 400 watts (1/2 HP).
Within DC motors, there are two main types: brushed and brushless. While brushed motors are designed for general-purpose variable speed applications, brushless motors are designed for more advanced requirements.
Different Types of DC motors
Brushed Motors
The brushes and commutator inside a brushed motor mechanically commutate the motor windings as it runs, and it continues rotation as long as its power supply is connected. Brushed motors are easy to control (by varying the voltage for speed and torque), but the brushes require periodic maintenance and replacement and therefore have an estimated lifespan of 1,000~1,500 hours (more or less due to operating conditions). While they're considered more efficient than AC motors, they suffer losses in efficiency compared to brushless motors due to resistance in the winding, brush friction, and eddy-current losses.
Brushed motors are offered in multiple types: permanent magnet brush type, shunt-wound type, series-wound type, and compound-wound type. A typical application for a brushed motor includes RC cars and windshield wipers.
Since Oriental Motor doesn't manufacture brushed motors, we offer limited information on brushed motors.
Brushless Motors
Brushless motor systems offer better speed control and performance than brushed motors due to electrical commutation and closed-loop feedback but require drivers to work. This raises the overall cost per axis, but it may be a necessary cost for applications requiring more advanced speed control features or closed-loop functions, such as continuous duty conveyors requiring multiple speeds or status monitoring.
Brushless motor and driver systems are often compared with AC motor and VFD systems for their advantages in size, weight, and efficiency especially for applications such as conveyors or mobile robotics.
Here's a comparison between a 200 W AC motor and VFD vs a BLE2 Series brushless motor and driver.
We also show a speed torque curve of a brushless motor system compared to an AC motor and VFD system of equivalent frame size.
Brushless Motor + Driver
AC Motor + VFD
How Do They Work?
Compared to a brushed motor, a brushless motor simply requires a driver to understand its feedback signals and commutate the motor windings in the right sequence and timing.
For Oriental Motor's brushless motors, a three-phase winding in a "star" connection is used on a radially segmented permanent magnet rotor. A built-in Hall effect sensor IC or optical encoder sends signals to the drive circuit to determine rotor position for the purpose of phase excitation timing.
On brushless motors with Hall effect IC, three Hall effect sensors are placed within the stator at 120 degrees apart and send digital signals as they sense the north and south poles go by as the rotor rotates. These signals tell the driver what speed the motor is running at and when to energize the next set of winding coils at exactly the right time.
Want to know more? Learn about the differences between brushed vs brushless motors.
Oriental Motor's brushless motor systems are paired with their own dedicated drivers for guaranteed specifications and quick setup. Various gearing options are offered for flexibility. Closed-loop feedback is done by either encoder or hall-effect sensors, and each driver offers different features and functions to suit various applications.
The Brushless Motor Advantage
Advantages vs Brushed Motors
Advantages vs AC Motors
- Longer life
- Lower electrical noise (EMI)
- Lower audible noise
- No arcing or sparks
- More available torque
- Lower temperature
- Cleaner
- Smaller size
- More efficient
- Smaller size
- Lower temperature
- Constant torque
Ideal for Positioning: Stepper Motors
Stepper Motors
Technically, brushless motors also include stepper motors, which are designed for positioning applications due to their high pole count, holding torque, and superior stop accuracy. Compared to 10 or 12 poles on a brushles motor rotor, a stepper motor rotor has at least 50 poles or even 100 poles. Similar to a brushless motor, a stepper motor requires a driver to operate. Unlike a brushless motor, a stepper motor can operate without feedback.
Also, duty cycles for open-loop stepper motor systems must be limited since they generate high heat. Generally, stepper motors use full current at all times, while brushless motors only use what it needs according to the load, speed, or acceleration/deceleration parameters. Oriental Motor provides 2-phase (1.8°) and 5-phase (0.72°) motors as well as unipolar and bipolar constant current chopper drivers.
A stepper motor's precise stopping ability comes from a toothed and magnetized rotor and a toothed electromagnetic stator.
A standard 1.8° stepper motor has 50 poles from 50 teeth in the rotor and 8 poles in the stator.
How Do They Work?
Like a brushless motor, a stepper motor also requires a driver to electrically commutate its windings. With higher pole count, comes better control. Using a two-phase excitation method for maximum torque, a driver excites two motor phases at a time and operates by pulses and steps. This means that each command pulse received by the driver will make the motor take a small "step", and the frequency of these command pulses determines the motor speed. Also, a stepper motor driver can energize specific poles in the motor, generate holding torque at standstill, and hold the rotor at specific positions.
Imagine stopping at position "1" in the simplified 4-step rotation diagram below. If the driver can provide a steady amount of current and energize phases "A" and "B" continuously, the motor will hold at position "1". If the driver excites the next two phases, then the motor will move to the next step. If the driver follows the step sequence and switches faster, the stepper motor will seem like it's rotating continuously.
In the real world, a 2-phase standard 1.8° stepper motor moves a quarter of a tooth pitch on a 50 tooth rotor for every command pulse its driver receives and therefore needs 200 steps to rotate one full revolution. The ability to generate holding torque at standstill helps to maintain stop position accuracy.
Open-loop stepper motors may suffice for general repeated positioning applications. However, closed-loop stepper motors are available for advanced positioning applications requiring higher reliability and efficiency.
A stepper motor's speed torque curve is typically downward sloping; with the highest torque occurring during low speed, which means that it can be used for acceleration and deceleration. Unlike a brushless motor system, a stepper motor does not have a limited-duty region.
If you'd like to learn more, I have written separate notes about stepper motors. Please enjoy.
Learn about the differences between hybrid, PM, and VR stepper motors
Learn more about the differences between servo motors and stepper motors
Motor Selection Tip: Rule of Thumb
- Use AC motors for constant speed, DC brushed and brushless motors for speed control, and stepper motors for positioning applications.
- Calculate the required torque, load inertia, and speed by using our motor sizing tool.
- Select a motor that can satisfy the application's torque, load inertia, and speed requirements.
- Select a motor or a motor and driver series that uses your available power supply. Stepper motor systems with AC input drivers output more torque in the high-speed region than DC input drivers.
- Select a motor or a motor and driver combination that satisfies other application requirements, such as stop accuracy, speed range, electromagnetic brake control, or networking capabilities.
This blog post provides a general understanding of the many types of AC/DC motors in the market. In addition to performance differences, quality, cost, product breadth, lead times, and support can also be deciding factors. Finding a quality motor supplier that can guarantee performance, provide expert support for a wide range of products, and ship reliably can also be important.
Ready for a little practice? Which type of motor would you use for these applications?
Click the application GIFs below to see the recommended motors for these applications.
Washdown Conveyor
XYZ Table
Need immediate answers? Contact our team!