Brush DC Motor Guide - What Are Brush DC Motors?

8/14/2019 Brush DC Motor Guide - What Are Brush DC Motors?

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Brush DC Motor Guide

What is a Brush DC Motor?

A Brush DC Motor provides precision control of speed, driven by a direct current. Noted for a particularly highratio of torque to inertia, the Brush DC Motor has the potential to supply three to four times more torque than it’srated torque. If needed, it can even provide up to five times more, without stalling. The Brush DC Motor consistsof six different components: the axle, armature/rotor, commutator, stator, magnets, and brushes. The Brush DCMotor offers stable and continuous current, using rings to power a magnetic drive that operates the motor’sarmature. Perhaps one of the earliest used motors, the Brush DC Motor is commonly used because of theability 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 fromthe magnets they are facing, and causes the rotor to turn. The current shuts off at the rotor and makes a 180degree turn, causing each rotor to face the opposite magnet. As the current turns on again, the electricity flowsoppositely, sending another pulse that causes the rotor to turn once again. The brushes that are located withinthe 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 DCMotor. 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 Motorstator is stationary, while the rotor rotates with respect to the Brush DC Motor stator. When power is applied tothe 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 reachesalignment, the brushes in the Brush DC Motor move to the next commutator contacts, and energize the nextwinding. This results in a current reversal, thus causing the winding and Brush DC Motor stator magnets tomisalign again. This process repeatedly is what keeps a Brush DC Motor rotating.

Carbon Brushes

A key component to the Brush DC Motor is a device known as a carbon brush, which conducts current betweenstationary wires and moving parts. For a Brush DC Motor to work, the coils of the Brush DC Motor rotor must beconnected to complete an actual circuit. To do this, slip rings are affixed to the shaft of the Brush DC Motor, andbrushes are attached to the rings, which will be used to conduct the current. Carbon brushes are considered tobe both the most critical, yet weakest point of the Brush DC Motor. This is because they are highly susceptibleto wear, especially when running the Brush DC Motor outside of its parameters. The wearing of carbon brushesacts as a disadvantage to the Brush DC Motor, however they can be easily replaced. Although many peopleconsider 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 yourBrush DC Motor.

Brush DC Motor Types

There are five basic Brush DC Motor types:

Brushed shunt mount Brush DC Motor: Abrushed shunt wound Brush DC Motor will runat constant speed regardless of the load.



Brushed series wound motor:Speed varies automatically with the load,increasing as the load decreases. This serieswound motor is usually limited when heavypower demand is necessary.

Brushed compound Brush DC Motor: A combination of the brushed shunt and brushed series woundmotors, combining the characteristics of both. These brushed compound motors are usually used whensevere 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 energyefficient 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 lowspeeds. This is achieved by separately generating a high stator field current and enough armaturevoltage 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 isfound in household applications. It can also be found in the industrial world because of its versatility in alteringits 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 andaffordability. Many automotive manufacturers use them for power windows, seats, etc. However, the Brush DCMotor 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 automaticcar windows and seat adjustments are operated by a Brush DC Motor. The Brush Motor has been anautomotive industry favorite because of its relatively low cost and simple design. A Brush DC Motor comes in alldifferent sizes, and torque and speed specifications. The Brush DC Motor can be a good candidate for virtuallyany 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 voltageapplied 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 beendeveloped 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 themajority of torque control and variable speed applications. The following discusses the advantages anddisadvantages 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 acontroller 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 createdin 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 "permanentmagnet DC motor" (PMDC). If created by electromagnetic windings, the DC Brush Motor is oftensaid to be a "shunt wound Brush DC Motor" (SWDC). Today, because of cost-effectiveness andreliability, the PMDC motor is the motor of choice for applications involving a fractional horsepowerBrush 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 changingelectromagnetic flux coming from windings located on the rotor of the DC Brush Motor. Themagnetic poles of the armature field will attempt to line up with the opposite magnetic polesgenerated by the stator field. Next, the section of the rotor where the electricity enters the rotorwindings is called the commutator. The electricity is carried between the brush motor rotor andthe stator by conductive graphite-copper brushes (mounted on the rotor) which contact rings onstator.

Imagine power is supplied:

A Brush DC Motor typically rotates toward the pole alignment point. Just as the DC Brush Motorwould get to this point, the brushes jump across a gap in the stator rings. Momentum carries thebrush motor forward over this gap. When the brushes get to the other side of the gap, theycontact the stator rings again and the polarity of the voltage is reversed in this set of rings! TheBrush DC Motor begins accelerating again, to the opposite set of poles. (The momentum hascarried 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 presentto 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 fasterthe 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 (aBrush 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 arerated 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 toabout 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 thefact 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 BrushDC Motors.

• NOTE: Specialty Brush DC Motors for use in mobile applications are typically rated 12, 24, or 48VDC. Other tiny brush motors can be rated as low as 5 VDC. This type of Brush DC Motor is verypopular among hobbyists.• In a Brush DC Motor, torque control is also easy to accomplish. Output torque is proportional tocurrent. Therefore, if the current is limited, you have also limited the torque which the brush motorcan achieve.• This fact makes the Brush DC Motor ideal for delicate applications such as textile manufacturing.• Simple and inexpensive control designThe result of this design is that variable speed or variable torque electronics are easy to designand 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 horsepowerapplications by the SCR and PWM drives (sometimes referred to as controls), which offerrelatively precisely control voltage and current. Common controls for Brush DC Motors areavailable at the low-end of the product offering (up to 2 horsepower). The cost will depend on theaccuracy requirement, but many brush motors can be accompanied with controllers covering awide 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 DCMotor can cost half the price of their Brushless DC Motor counterparts. However, the brushes within the BrushDC Motor are apt to wear and require replacement, making it a higher-maintenance option, because of the longrun 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 electromagneticwindings or permanent magnets. The rotor can also be called the armature. It consists of one or more windingsthat produce a magnetic field when energized, causing the motor to turn. The commutator is a copper sleevethat is located on the rotor’s axis. This performs mechanical commutation of the windings, eliminating the needfor a controller to switch the current. The brushes located inside the Brush DC Motor generate a charge byrubbing the different parts of the commutator. It is because of this rubbing, that the brushes and commutatorare 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, althoughactual service life varies. Brush DC Motor design, operating current, speed, voltage, and other conditions are allcontributing 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 theBrush DC Motor from potentially encountering any type of vapors, moisture, dirt, oils, or debris. Ensure allmounting bolts are fastened tightly, and the operation of the Brush DC Motor is in accordance with the giveninstructions on installation. A Brush DC Motor generally tends to have increased maintenance requirements incomparison 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 thecommutator and the brushes will cause debris and contaminants to settle within the Brush DC Motor, requiringcleaning as well. Most commonly this occurs between the commutator and the shaft of the Brush DC Motor, aswell 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 Motorand other electrical and electronic devises in the system. Dry, warm environments may increase the wear of thebrushes, and quicken the breakdown of the commutator and bearings, ultimately shortening the lifetime of themotor. 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 potent ially increase the viscosityof 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, serviceand repair of a Brush DC Motor system. Failure to comply with these precautions violates safety standards ofdesign, manufacture and intended use of the Brush DC Motor and controller (if also used). Please note thateven 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 isultimately 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 ofelectrical/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 elementsby an adequate cover, while still providing adequate air flow and cooling. Moisture may cause an electricalshock hazard and/or induce system breakdown. Due consideration should be given to the avoidance of liquidsand vapors of any kind. Contact the factory should your application require specific IP ratings. It is wise to installthe 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 contactwith live circuitry. No work should be performed while power is applied. Don’t plug in or unplug the connectorswhen power is ON. Wait for at least 5 minutes before doing inspection work on the Brush DC Motor andcontroller system after turning power OFF, because even after the power is turned off, there will still be someelectrical 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, dril ling, 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 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 isknown.

Determining Speed and Current Flow for a Brush DC Motor:

W = (VS – I x Rmt) / KE and I = TL / KT + INLWhere: W = Speed, VS = Supply Voltage, Rmt = Motor Terminal Resistance, I = Current, T = LoadTorque, 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 anexperiment 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 circularmagnetic field.

While Michael Faraday is often credited for the invention of the electric motor, his experiment is really just a labdemonstration; it can’t be harnessed for useful work. Several other scientists such as Joseph Henry and WilliamSturgeon based their work on Faraday's experiment and theories. By the late nineteenth century the design ofBrush DC Motor had become well-established. The demand for the Brush DC Motor has skyrocketed since thenas a necessity in industrial applications.

Brush DC Gearmotors

Brush DC Gearmotors provide an affordable and simple

solution to high starting torque and low inertia applications. Brush DC Permanent Magnets offer lower currentdrain for more efficient battery operation in portable applications. When the power is removed, the PermanentMagnets provide less shaft coast. Permanent Magnet Brush DC Gearmotors can be reversed by simplychanging the polarity of the line connection. Brush DC Gearmotor performance varies by the quality of itscomponents. 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 withPlanetary Gearboxes, Permanent Magnet DC Motors with Spur Gearboxes, and Standard Permanent MagnetDC Motors with Gearboxes, an extension of the DC Spur Gearmotor line.



Accessories

Anaheim Automation carries a line of Brush DC Drivers and Controllers, along with a comprehensive line ofBrush 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 atdifferent 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 generatedfrom the controller. If necessary replace the fan guard, and check to make sure the armature is not rubbingagainst the magnets due to misalignment. The Brush DC Motor may need to be replaced. Depending on theoriginal 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 Motorto handle. Measure the amp draw next to the motor’s full load amp rating to be sure the Brush DC Motor isappropriately sized for the application. Also check the settings on the controller, and the armature. Torque andcompensation 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 maxspeeds less than 1000 RPM, and a Brush DC Motor only if max speeds exceed 1000 RPM. Next, decide whattorque your application requires. When using a gearbox, be sure to select the appropriate gear ratio by dividingthe maximum speed of the gearbox by the max desired output speed (See ‘Formulas for a Brush DC Motor’ formore information).

After you have determined speed and torque requirements, select a frame size for your Brush DC Motor that willfit 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 andsupply 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 berunning. 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 anytype 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 motorBrushed series wound motorBrushed compound motorBrushed permanent magnet motorBrushed 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?

A: Electromagnetism

Q: What is the equation used to calculate motor speed in RPM?

A: =V-(Tt/Kt+I0)/Ke×Rt 1000



Q: List 3 basic applications of the Brush DC Motor:

A: Household appliancesAutomobilesRadio-Controlled Toys(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 motornoise.

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 thebetter choice. Applications with higher torque, higher current consumption, lower efficiency, and higher audiblenoise 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 inpractice, some backlash should be allowed to prevent jamming. This is accounted for especially in reversingmechanical designs. Generally the greater the accuracy, the smaller the backlash needed. Backlash is mostcommonly 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. TheBrush DC Motor life can be affected by the speed of operation. Operating at a lower voltage means leesbrush/commutator wear on the Brush DC motor, also lower current consumption means longer Brush DC Motorlife.

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 BrushlessDC 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 bycombining the characteristics of both.

Brushed Permanent Magnet Motor - contains permanent magnets inside, which eliminates the need forexternal 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 byseparately 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. Thisoccurs 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 amongthe 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.

© 2011 Anaheim Automation Inc - All RightsReserved

Brush DC Motor Guide - What Are Brush DC Motors?

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