What is a Brush DC Motor?
A Brush DC Motor provides precision control of speed, driven by a direct current. Noted for a particularly high ratio of torque to inertia, the Brush DC Motor has the potential to supply three to four times more torque than it's rated torque. If needed, it can even provide up to five times more, without stalling. The Brush DC Motor consists of six different components: the axle, armature/rotor, commutator, stator, magnets, and brushes. The Brush DC Motor offers stable and continuous current, using rings to power a magnetic drive that operates the motor's armature. Perhaps one of the earliest used motors, the Brush DC Motor is commonly used because of the ability to vary the speed-torque ratio in almost any way.
Block Diagram for Systems That Use a Brush DC Motor
How does a Brush DC Motor work?
A Brush DC Motor consists of two magnets facing the same direction, that surrounding two coils of wire that reside in the middle of the Brush DC Motor, around a rotor. The coils are positioned to face the magnets, causing electricity to flow to them. This generates a magnetic field, which ultimately pushes the coils away from the magnets they are facing, and causes the rotor to turn. The current shuts off at the rotor and makes a 180 degree turn, causing each rotor to face the opposite magnet. As the current turns on again, the electricity flows oppositely, sending another pulse that causes the rotor to turn once again. The brushes that are located within the Brush DC Motor turn it off an on when instructed, by transferring the electricity from the rotor.
Brush DC Motor Basics
The operation of any Brush DC Motor is based on electromagnetism. The Brush DC Motor has two terminals; when voltage is applied across the two terminals, a proportional speed is outputted to the shaft of the Brush DC Motor. A Brush DC Motor consists of two pieces: the stator which includes the housing, permanent magnets, and brushes, and the rotor, which consists of the output shaft, windings and commutator. The Brush DC Motor stator is stationary, while the rotor rotates with respect to the Brush DC Motor stator. When power is applied to the Brush DC Motor rotor windings, the polarity of the winding and stator magnets is misaligned, and the Brush DC Motor rotor rotates until it is almost aligned with the stator magnets. As the Brush DC Motor rotor reaches alignment, the brushes in the Brush DC Motor move to the next commutator contacts, and energize the next winding. This results in a current reversal, thus causing the winding and Brush DC Motor stator magnets to misalign again. This process repeatedly is what keeps a Brush DC Motor rotating.
A key component to the Brush DC Motor is a device known as a carbon brush, which conducts current between stationary wires and moving parts. For a Brush DC Motor to work, the coils of the Brush DC Motor rotor must be connected to complete an actual circuit. To do this, slip rings are affixed to the shaft of the Brush DC Motor, and brushes are attached to the rings, which will be used to conduct the current. Carbon brushes are considered to be both the most critical, yet weakest point of the Brush DC Motor. This is because they are highly susceptible to wear, especially when running the Brush DC Motor outside of its parameters. The wearing of carbon brushes acts as a disadvantage to the Brush DC Motor, however they can be easily replaced. Although many people consider carbon brushes in a Brush DC Motor to be a "Black Art," they still serve a great purpose when operated in the proper conditions. They tend to yield an excellent life, and perform an amazing function for your Brush DC Motor.
Brush DC Motor Types
There are five basic Brush DC Motor types:
Brushed shunt mount Brush DC Motor: A brushed shunt wound Brush DC Motor will run at constant speed regardless of the load.
Brushed series wound motor: Speed varies automatically with the load, increasing as the load decreases. This series wound motor is usually limited when heavy power demand is necessary.
Brushed compound Brush DC Motor: A combination of the brushed shunt and brushed series wound motors, combining the characteristics of both. These brushed compound motors are usually used when severe starting conditions are met and constant speed.
Brushed permanent magnet Brush Motor: As the name implies, these contain permanent magnets, which eliminate the need for external field current. This design yields a smaller, lighter, and energy efficient Brush DC Motor, and are the type of Brush DC Motor Anaheim Automation carries.
Brushed separately excited Brush Motor: These are used for their high torque capability at low speeds. This is achieved by separately generating a high stator field current and enough armature voltage to produce the required rotor torque current.
Where is the Brush DC Motor used?
Although the brushless DC motor has surpassed the Brush DC Motor because of its longetivity and reliability, the Brush DC Motor is still appropriately chosen for many applications. Most commonly, the Brush DC Motor is found in household applications. It can also be found in the industrial world because of its versatility in altering its torque to speed ratio.
What Industries Use the Brush DC Motor?
The Brush DC Motor is particularly a favorite in the automotive industry because of its simplicity and affordability. Many automotive manufacturers use them for power windows, seats, etc. However, the Brush DC Motor can be found in nearly every industry ranging from computers to manufacturing.
Brush DC Motor Applications
Brush DC Motors are used in a wide range of applications, ranging from toys to Jacuzzi pumps. Most automatic car windows and seat adjustments are operated by a Brush DC Motor. The Brush Motor has been an automotive industry favorite because of its relatively low cost and simple design. A Brush DC Motor comes in all different sizes, and torque and speed specifications. The Brush DC Motor can be a good candidate for virtually any motion control endeavor.
How is a Brush DC Motor Controlled?
A Brush DC Motor provides simple speed control without the need of complicated electronics. The voltage applied to a Brush DC Motor is proportional to rotational speed, while torque is proportional to the current. By applying variable supply voltage, speed control can be achieved. Electronic speed controls have been developed to provide a more accurate and precise operation. Changing rotational direction can be done by reversing the field or armature connections.
Advantages and Disadvantages of a Brush DC Motor
The DC Brush Motor is one of the earliest of all electrical motor designs. It is usually the motor of choice for the majority of torque control and variable speed applications. The following discusses the advantages and disadvantages of using a Brush DC Motor in machinery and processes.
Advantages - Brush DC Motor
The DC Brush Motor is one of the earliest of all electrical motor designs. It is usually the motor of choice for the majority of torque control and variable speed applications. The following discusses the advantages and disadvantages of using a Brush DC Motor in machinery and automated processes.
• The Brush DC Motor has a simple construction, therefore may not require a controller. When a controller is chosen, it is typically a simple and inexpensive drive design.
• Understandable design technology facilitates in the quick application of the DC Brush Motor
• The design of the Brush DC Motor is quite simple, in that a permanent magnetic field is created in the by either of two means; permanent magnets or electro-magnetic windings
• If the field is created by permanent magnets, a Brush DC Motor is said to be a "permanent magnet DC motor" (PMDC). If created by electromagnetic windings, the DC Brush Motor is often said to be a "shunt wound Brush DC Motor" (SWDC). Today, because of cost-effectiveness and reliability, the PMDC motor is the motor of choice for applications involving a fractional horsepower Brush DC Motor, as well as most applications up to about 2.0 horsepower.
• Opposing the stator field is the armature field, which is generated by a changing electromagnetic flux coming from windings located on the rotor of the DC Brush Motor. The magnetic poles of the armature field will attempt to line up with the opposite magnetic poles generated by the stator field. Next, the section of the rotor where the electricity enters the rotor windings is called the commutator. The electricity is carried between the brush motor rotor and the stator by conductive graphite-copper brushes (mounted on the rotor) which contact rings on stator.
Imagine power is supplied:
A Brush DC Motor typically rotates toward the pole alignment point. Just as the DC Brush Motor would get to this point, the brushes jump across a gap in the stator rings. Momentum carries the brush motor forward over this gap. When the brushes get to the other side of the gap, they contact the stator rings again and the polarity of the voltage is reversed in this set of rings! The Brush DC Motor begins accelerating again, to the opposite set of poles. (The momentum has carried the brush motor past the original pole alignment point.) This continues as the brush motor rotates. Typically a Brush DC Motor has several sets of windings or permanent magnets present to smooth out the motion.
Speed Control for a Brush DC Motor
• Controlling the speed of a Brush DC Motor is simple. The higher the armature voltage, the faster the rotation. This relationship is linear to the Brush DC Motor's maximum speed.
• The maximum armature voltage which corresponds to the rated speed of a Brush DC Motor (a Brush DC Motor is usually given a rated speed and a maximum speed, such as 1750/2000 rpm), are available in certain standard voltages, which roughly increase in conjunction with horsepower.
• The smallest industrial-type Brush DC Motor is rated 90 VDC and 180 VDC. Larger units are rated at 250 VDC and even higher (dependent upon the individual manufacturer).
• Most industrial Brush DC Motors operate reliably over a speed range of about 20:1 - down to about 5-7% of base speed. This is much better performance than the comparable AC motor. This fact is in part due to the fact of the mere simplicity of control. However, it is also partly due to the fact that most industrial Brush DC Motors were designed with variable speed operations in mind. The addition of heat dissipation features / devices provided for lower operating speeds of Brush DC Motors.
• NOTE: Specialty Brush DC Motors for use in mobile applications are typically rated 12, 24, or 48 VDC. Other tiny brush motors can be rated as low as 5 VDC. This type of Brush DC Motor is very popular among hobbyists.
• In a Brush DC Motor, torque control is also easy to accomplish. Output torque is proportional to current. Therefore, if the current is limited, you have also limited the torque which the brush motor can achieve.
• This fact makes the Brush DC Motor ideal for delicate applications such as textile manufacturing.
• Simple and inexpensive control design
The result of this design is that variable speed or variable torque electronics are easy to design and manufacture. Varying the speed of a Brush DC Motor requires little more than an appropriate potentiometer. In practice, these have been replaced for all but sub-fractional horsepower applications by the SCR and PWM drives (sometimes referred to as controls), which offer relatively precisely control voltage and current. Common controls for Brush DC Motors are available at the low-end of the product offering (up to 2 horsepower). The cost will depend on the accuracy requirement, but many brush motors can be accompanied with controllers covering a wide range of prices.
Disadvantages - Brush DC Motor
• A Brush DC Motor is less reliable in control at lowest speeds
• A Brush DC Motor is physically larger than other motors producing equivalent torque
• A Brush DC Motor is considered high-maintenance, which is not true of brushless DC motors
• A Brush DC Motor are vulnerable to dust which decreases performance
How much do Brush DC Motors cost?
The Brush DC Motor has a relatively inexpensive start up cost and simple design. In some cases, the Brush DC Motor can cost half the price of their Brushless DC Motor counterparts. However, the brushes within the Brush DC Motor are apt to wear and require replacement, making it a higher-maintenance option, because of the long run costs.
Physical Properties of a Brush DC Motor
A typical Brush DC Motor contains six components: Stator, Rotor/Armature, Commutator, and Brushes, an axle, and magnets. The stator surrounds the rotor, and generates a magnetic field by means of electromagnetic windings or permanent magnets. The rotor can also be called the armature. It consists of one or more windings that produce a magnetic field when energized, causing the motor to turn. The commutator is a copper sleeve that is located on the rotor's axis. This performs mechanical commutation of the windings, eliminating the need for a controller to switch the current. The brushes located inside the Brush DC Motor generate a charge by rubbing the different parts of the commutator. It is because of this rubbing, that the brushes and commutator are prone to wear.
Lifetime for a Brush DC Motor
The life of the brushes, bearings, and gearbox (if used) all play a role in the longevity of a Brush DC Motor. Most commonly, Brush DC Motor life expectancies range from 2,000 to 5,000 hours of operation, although actual service life varies. Brush DC Motor design, operating current, speed, voltage, and other conditions are all contributing factors.
Required Maintenance for a Brush DC Motor
Always make certain that the Brush DC Motor, as well as the motor environment are kept clean, to prevent the Brush DC Motor from potentially encountering any type of vapors, moisture, dirt, oils, or debris. Ensure all mounting bolts are fastened tightly, and the operation of the Brush DC Motor is in accordance with the given instructions on installation. A Brush DC Motor generally tends to have increased maintenance requirements in comparison to those of AC motors, because many of the motor's components are constantly interacting with one another. Over time, the brushes will wear and will require replacement. Also, the interaction between the commutator and the brushes will cause debris and contaminants to settle within the Brush DC Motor, requiring cleaning as well. Most commonly this occurs between the commutator and the shaft of the Brush DC Motor, as well as between the winding and the armature.
Environmental Considerations of a Brush DC Motor
The environment in which a Brush DC Motor will be used plays a major role in the life cycle of a Brush DC Motor and other electrical and electronic devises in the system. Dry, warm environments may increase the wear of the brushes, and quicken the breakdown of the commutator and bearings, ultimately shortening the lifetime of the motor. Running the Brush DC Motor in a cooler environment, with external cooling by forced air, may cause the Brush DC Motor to perform better. However, extreme drops in temperature can potentially increase the viscosity of the Brush DC Motor lubricants, causing it to run at a higher current.
The following environmental and safety considerations must be observed during all phases of operation, service and repair of a Brush DC Motor system. Failure to comply with these precautions violates safety standards of design, manufacture and intended use of the Brush DC Motor and controller (if also used). Please note that even with a well-built Brush DC Motor, products operated and installed improperly can be hazardous. Precaution must be observed by the user with respect to the load and operating environment. The customer is ultimately responsible for the proper selection, installation, and operation of the Brush DC Motor system.
The atmosphere in which a Brush DC Motor is used must be conducive to good general practices of electrical/electronic equipment. Do not operate the Brush DC Motor in the presence of flammable gases, dust, oil, vapor or moisture. For outdoor use, the Brush DC Motor and controller must be protected from the elements by an adequate cover, while still providing adequate air flow and cooling. Moisture may cause an electrical shock hazard and/or induce system breakdown. Due consideration should be given to the avoidance of liquids and vapors of any kind. Contact the factory should your application require specific IP ratings. It is wise to install the Brush DC Motor and controller in an environment which is free from condensation, dust, electrical noise, vibration and shock.
Additionally, it is preferable to work with the Brush DC Motor system in a non-static, protective environment. Exposed circuitry should always be properly guarded and/or enclosed to prevent unauthorized human contact with live circuitry. No work should be performed while power is applied. Don't plug in or unplug the connectors when power is ON. Wait for at least 5 minutes before doing inspection work on the Brush DC Motor and controller system after turning power OFF, because even after the power is turned off, there will still be some electrical energy remaining in the capacitors of the internal circuit of the controller.
IMPORTANT: Plan the installation of the Brush DC Motor and controller in a system design that is free from debris, such as metal debris from cutting, drilling, tapping, and welding, or any other foreign material that could come in contact with circuitry. Failure to prevent debris from entering the Brush DC Motor motor system can result in damage and/or shock.
Formulas for a Brush DC Motor
Calculating Motor Speed, RPM for a Brush DC Motor:
=V-(Tt/Kt+I0)/Ke×Rt ಏ 1000
Where: V= supply voltage, V; Tl = load torque, oz-in.; Kt = motor torque constant, oz-in./A; I0 = motor no-load current, A; Rt = motor terminal resistance, Ohms; Ke = motor voltage constant, V/1,000 rpm. It is possible to solve for an unknown quantity (voltage or current) when speed is known.
Determining Speed and Current Flow for a Brush DC Motor:
W = (VS – I x Rmt) / KE and I = TL / KT + INL
Where: W = Speed, VS = Supply Voltage, Rmt = Motor Terminal Resistance, I = Current, T = Load Torque, KE = Back – EMF Constant
Brush DC Motor History
The history of the Brush DC Motor can be traced back to the 1830's, when Michael Faraday set to devise an experiment to demonstrate whether or not a current-carrying wire produced a circular magnetic field around it. Michael Faraday's experiment turned out to be a success; the current-carrying wire did produce a circular magnetic field.
While Michael Faraday is often credited for the invention of the electric motor, his experiment is really just a lab demonstration; it can't be harnessed for useful work. Several other scientists such as Joseph Henry and William Sturgeon based their work on Faraday's experiment and theories. By the late nineteenth century the design of Brush DC Motor had become well-established. The demand for the Brush DC Motor has skyrocketed since then as a necessity in industrial applications.
Brush DC Gearmotors provide an affordable and simple solution to high starting torque and low inertia applications. Brush DC Permanent Magnets offer lower current drain for more efficient battery operation in portable applications. When the power is removed, the Permanent Magnets provide less shaft coast. Permanent Magnet Brush DC Gearmotors can be reversed by simply changing the polarity of the line connection. Brush DC Gearmotor performance varies by the quality of its components. Some key quality factors to consider are gearing, hobbing, housings, bearings and lubrication.
Anaheim Automation offers three different types of Brush DC Gearmotors: Permanent Magnet DC Motors with Planetary Gearboxes, Permanent Magnet DC Motors with Spur Gearboxes, and Standard Permanent Magnet DC Motors with Gearboxes, an extension of the DC Spur Gearmotor line.
Anaheim Automation carries a line of Brush DC Drivers and Controllers, along with a comprehensive line of Brush DC Gearmotors. Accessories are also available through Anaheim Automation, including single-ended and differential encoder cables with four, six, and eight leads, cable lengths up to 16 feet, and encoder centering tools. Additionally, Anaheim Automation offers an extended line of stepper, brushless and servo motors at different prices.
Troubleshooting a Brush DC Motor
Note: Exercise caution when troubleshooting your Brush DC Motor. Ensure safety guards are in place, disconnect any power, and discharge all capacitors prior to inspecting the Brush DC Motor.
Problem: After installation, Brush DC Motor does not start.
Solution: Ensure the Brush DC Motor is correctly wired, and verify the appropriate voltage is being generated from the controller. If necessary replace the fan guard, and check to make sure the armature is not rubbing against the magnets due to misalignment. The Brush DC Motor may need to be replaced. Depending on the original cost of the motor, the brushes should be replaced. For Anaheim Automation Brush DC Motors however, the entire motor is replaced as it is the most cost-effective approach.
Problem: Brush DC Motor loses power while running.
Solution: Check the load being applied to the motor. Changes in load may be too much for the Brush DC Motor to handle. Measure the amp draw next to the motor's full load amp rating to be sure the Brush DC Motor is appropriately sized for the application. Also check the settings on the controller, and the armature. Torque and compensation settings may be slightly off, and the armature needs an open connection.
Problem: Brush DC Motor fails to start after having been working.
Solution: If this is the case, the brushes may have worn down and are unable to interact with the commutator. Take apart the Brush DC Motor and check both the commutator and armature for any burnt bars or a burnt coil. Finally, ensure the voltage is emitting out of the controller.
Problem: Brush DC Motor is not accelerating quick enough.
Solution: Check the length of the brushes to ensure they are not worn out. Look for any defective bearings (bearings generating loud noise is a sign); replace or lubricate bearings if needed.
Problem: The Brush DC Motor is running in reverse.
Solution: Double check the wiring arrangement, you probably need to interchange the two leads.
Problem: The Brush DC Motor makes a clicking sound.
Solution: Remove burr from the armature with a commutator stone.
How to Select a Brush DC Motor
The first step in selecting the appropriate Brush DC Motor is to determine your maximum required speed. After this is determined, decide whether or not a gearbox is required. Typically a gearmotor should be used for max speeds less than 1000 RPM, and a Brush DC Motor only if max speeds exceed 1000 RPM. Next, decide what torque your application requires. When using a gearbox, be sure to select the appropriate gear ratio by dividing the maximum speed of the gearbox by the max desired output speed (See ‘Formulas for a Brush DC Motor' for more information).
After you have determined speed and torque requirements, select a frame size for your Brush DC Motor that will fit your application, and also generate the amount of torque needed. Then, select the appropriate windings. Select the winding that will most closely deliver the desired current draw and speed, given the load torque and supply voltage. (See ‘Formulas for a Brush DC Motor' for more information).
A general rule to keep in mind when selecting any type of Brush DC Motor is the environment in which it will be running. Be sure to consider what the Brush DC Motor will be exposed to (excessive heat, fluids, debris, etc). Also keep in mind any standards or regulations that have been set, the cost of the Brush DC Motor, and any type of special customization options that may be available from the manufactuer that will better suit your application requirements. Anaheim Automation provides customization of motors and controls, however, minimum purchase requirements may apply.
Brush DC Motor Quiz
Q: What is the most critical component of a Brush DC Motor?
A: Carbon Brushes
Q: List the five basic Brush DC Motor types:
A: Brushed shunt mount motor
Brushed series wound motor
Brushed compound motor
Brushed permanent magnet motor
Brushed separately excited motor.
Q: List the four components of a Brush DC Motor:
A: Stator, Rotor/Armature, Commutator, and Brushes
Q: What is the basic principle in which a Brush DC Motor operates on?
Q: What is the equation used to calculate motor speed in RPM?
A: =V-(Tt/Kt+I0)/Ke×Rt ಏ 1000
Q: List 3 basic applications of the Brush DC Motor:
A: Household appliances
(many more could be listed)
Q: True or False: The long lifetime of Carbon Brushes is what makes the Brush DC Motor a favorite to the Brushless DC Motor alternative.
A: False. Carbon Brushes are prone to wear, giving the Brush DC Motor a disadvantage in some circumstances.
Q: What is the life expectancy range for a Brush DC Motor in hours?
A: Between 2,000-5,000 operating hours
Brush DC Motor FAQs
Q: What variables contribute to Brush DC Motor noise?
A: Motor mounting in application, load and speed of the motor, and type of bearings all play a role in motor noise.
Q: When do I use a Planetary, and when do I use a Spur Gearbox?
A: For a low current consumption, low noise, and high-efficiency application, a Spur Gearbox would be the better choice. Applications with higher torque, higher current consumption, lower efficiency, and higher audible noise levels, one should consider a Planetary Gearbox.
Q: What is Backlash?
A: Backlash is the clearance between mating components. Theoretically, backlash should be zero, but in practice, some backlash should be allowed to prevent jamming. This is accounted for especially in reversing mechanical designs. Generally the greater the accuracy, the smaller the backlash needed. Backlash is most commonly created by cutting the teeth deeper into the gears than the ideal depth. Another way of introducing backlash is by increasing the center distances between the gears.
Q: Does a Brush DC Motor need to run at the rated voltage?
A: No, however it is recommended to run the Brush DC Motor slower or less than the nominal voltage. The Brush DC Motor life can be affected by the speed of operation. Operating at a lower voltage means lees brush/commutator wear on the Brush DC motor, also lower current consumption means longer Brush DC Motor life.
Q: Are Anaheim Automation's Brush DC Motors reversible?
A: Yes, this can be easily done to by reversing the polarity on the Power Supply.
Q: What is the primary difference between a Brush DC Motor and a Brushless DC Motor?
A: Because of brush wear, a Brush DC Motor requires more maintenance, and has shorter life than Brushless DC Motors. Brushless DC Motors require the use of an Electrical Speed Controller, but offer higher efficiency.
Brush DC Motor Glossary
Armature – the component of the motor that produces power. It can be located on either the stator or the rotor.
Brush – mechanism that conducts current in between moving parts and stationary wires.
Brushed Compound Motor - a combination of the brushed shunt and brushed series wound motors by combining the characteristics of both.
Brushed Permanent Magnet Motor - contains permanent magnets inside, which eliminates the need for external field current. This design yields a smaller, lighter, and energy-efficient Brush Motor.
Brushed Separately Excited Motor - used for its high torque capability at low speeds. This is achieved by separately generating a high stator field current and enough armature voltage to produce the required rotor torque current.
Brushed Series Wound Motor - speed varies automatically with the load, increasing as the load decreases.
Brushed Shunt Wound Motor - run at constant speed regardless of the load.
Commutator – mechanism which reverses the direction of current in certain electric motors.
Direct Current – electrical charge constantly flows in the same direction. Opposite of an alternating current, where current periodically switches direction.
Electrical Power – electric circuits transferring electrical power at a given rate.
Overcurrent – can lead to damaged equipment due to excessive heat produced within a Brush DC Motor. This occurs because a larger amount of electric current is produced through the conductor.
Rotor – rotating device in an electric motor which rotates about the Brush DC Motor generating torque among the rotor's axis.
Stator – the part of the Brush DC Motor that is stationary.
Torque – the ability of a force to rotate a given object about an axis or fulcrum.