It is low cost, easy maintenance, and high torque that are considered the main advantages of brush motors. A 200-watt brush motor can be bought for 100-300 yuan, with a maintenance cost of only 50 yuan a year, whereas a brushless motor of the same power may sell for 500 to 1000 yuan and has a much longer maintenance cycle. So, they are appropriate for household appliances and industrial equipment, such as vacuum cleaners and electric drills.
Affordable Price
The ordinary price of a 200-watt brushed motor is about 100 to 300 yuan, while the same power of a brushless motor would cost about 500 to 1000 yuan. The unit cost of the brushed motor is about 50% lower than that of the brushless motor, saving millions in procurement costs annually.
The cost for replacing a traditional carbon brush ranges from 20 to 50 yuan, and the replacement time is normally 30 minutes, with labor cost of about 50 yuan. That can amount to 500 to 1000 yuan in maintaining a brushless motor, and even up to one week in a repair cycle. The average maintenance cost of the brushed motor amounts to 20%-30% of that for the brushless motor.
Brushed motors still account for about 65% of the global motor market, especially within household appliances and light industry, with 80% of models using brushed motors. Many consumers opt for vacuums priced less than 500 yuan, where the motor specification is a brushed motor.
In 2022, an educational company introduced a teaching robot that uses a brushed motor at a cost of as low as 30 yuan, but its minimum cost is 120 yuan with a brushless solution. The consumer response was tremendous; more than 85% of users have chosen this particular product because it is economical and satisfies the basic requirements of the people.
The hand-held electric drill is widely used in the construction site, generally using a brushed motor. The price of an average each is between 200 to 400 yuan, but the brushless kind usually exceeds 800 yuan. The average annual maintenance cost of each tool is only 50 yuan.
A home appliance manufacturer optimized the production process of a certain type of brushed motor, which had been reduced from 30 minutes to 15 minutes. Comparatively, the manufacturing time for a brushless motor was 30 minutes, so the added annual output reached 500,000 units, bringing the company an additional 150 million yuan in profit.
Considering the life of a household blender, an ordinary brushed motor may work for 5-8 years, while the brushless can serve for 10-15 years. As the renewal cycle for a blender is normally 5 years, a brushed motor can fully meet the requirement and costs half that of a brushless motor.
The result shows that even in light-load conditions, a 100-watt brushed motor works at an efficiency of 70%, only 10% lower compared with a brushless one.
Easy Maintenance
Carbon brushes, the commutator, the rotor, and the stator form most commonly known constituents of a conventional brushed motor. For carbon brush sets, the common price is about 20 to 50 yuan. And a whole process operation takes about 30 minutes in general.
Maintenance of a medium-sized industrial appliance with a brushed motor requires regular replacement of the carbon brushes and cleaning of the commutator. In all, this usually takes less than 1 hour. For brushless motors, maintenance normally involves more sophisticated equipment and technical support; a repair cycle can last from 2 to 5 days. The average downtime of production lines using brushed motors is 30% less compared to that of brushless motors.
Carbon brush wear is usually the cause of motor failure in household blenders or vacuum cleaners. Users can buy a set of carbon brushes for 10 to 20 yuan and replace them by themselves.
The average lifetime of its carbon brush in service for a 2-kilowatt industrial brushed motor is 500 hours, which means that, compared with a brushless motor, it needs maintenance more frequently, but changing its carbon brushes is very easy, and the operation cost each hour is only 1.5 yuan, while that of maintaining a brushless one is 3 yuan on average.
Almost all carbon brushes and commutators vary between 20-100 yuan, depending on specifications. The other 90% would definitely be sure to provide such maintenance parts for a brushed motor in less than 48 hours, allowing for faster fixing of the machinery.
Students and technicians can dismantle brushed motors for inside structure and working principles, replace parts easily to see some effects that they want in the repair. Every year, a technology laboratory costs only 3,000 yuan to replace the parts of brushed motors, while the replacement scheme of the brushless motors costs more than 10,000 yuan.
It uses a cooling system driven by a brushed motor, failure of which is easy to repair. Replacement of a set of brushes takes 45 minutes and costs 200 yuan while for a breakdown of a brushless motor, probably the whole motor system needs to be replaced, costing between 5,000-10,000 yuan.
Compared to the repair of a brushless motor, which requires professional engineers for complex electronic control adjustments, a brushed motor only requires basic mechanical skills. Technicians with basic training can replace carbon brushes in 15 minutes, while it takes two weeks and thousands of yuan to train a brushless motor repair technician.
It means an enterprise uses 100 industrial brushed motors and needs to repair them three times a year. Each repair costs about 150 yuan with a total cost of 45,000 yuan. Under the same scale, the maintenance cost of brushless motors is up to 150,000 yuan, nearly three times that of brushed motors.
Powerful Torque
A 500-watt brushed motor will have a starting torque of 2.5 Nm, while in the case of a brushless motor having the same wattage, it will provide a starting torque of only 1.8 Nm.
The electric winches applied on the construction sites all adopt brushed motors, whose biggest starting torque could be up to 10 Nm, while a brushless motor needs additional electronic control modules to achieve the same effect. The average price of a winch with a brushed motor is less than 4,000 yuan, while the brushless motor version is mostly over 6,000 yuan.
Other auxiliary devices in the automotive, such as windshield wipers, electric window lifters, and seat adjusters, also use some brushed motors. About 70% of the total number of auxiliary systems in the global automotive market use brushed motors. The starting torque of brushed motors normally lies in the range of 0.3 Nm to 0.5 Nm.
This could also mean that the brushed motor of a 1,200-watt vacuum cleaner provides 1.5 Nm torque to remove stubborn dirt on carpets in a very short period of time. More than 80% of sales in the market come from this kind of motor.
An electric tricycle for low-speed travel can generate a very powerful starting torque of 30 Nm by using a brushed motor. Although a brushless motor is superior in high-speed operation, the low-speed torque usually requires more electronic control optimizations.
It can achieve a maximum torque of 5 Nm with an 800-watt brushed motor electric impact drill-drive, powerful enough to make holes in the concrete wall. The market share of the brushed motor equipment is 65%, basically because of the powerful performance and its low price.
A 3-kilowatt industrial brushed motor can provide a starting torque of 15 Nm, while a brushless motor in the same situation often requires additional control devices to achieve similar performance.
A 1-kilowatt brushed motor has a maximum current density in its rotor of 20 A/mm², much higher than the 15 A/mm² of a brushless motor. This design feature provides brushed motors with more direct and powerful power output.
Simple Speed Regulation
Variable frequency drive VFD applied in AC motors in the case of industrial production can be continuously regulated from 0 to rated speed, the common regulation range is 1:10, and some high-performance systems can reach 1:100, while for DC motors, extra mechanical device or complicated electric circuit should be used.
With variable-frequency AC motors and rated power up to 1.5 kilowatts, the air conditioners can save energy up to 30% to 50%. By 2022 statistics, the inverter air conditioners have exceeded over 70% market shares.
Using speed control in a 10-kilowatt centrifugal pump can realize energy savings of 20% to 50%, saving tens of thousands of yuan in annual electricity costs. Therefore, many industrial enterprises choose AC motors with simple speed regulation to achieve the best energy-saving effect.
The acceleration and deceleration time of the 5-kilowatt elevator motor can be controlled within 2 seconds when using a variable frequency drive. More than 90% of new elevators all over the world use AC motors with adjustable speeds.
The production line might use an AC servo motor, for instance, which had a variable velocity from 100 rpm to 1,000 rpm in just 10 milliseconds.
Variable frequency AC motors find popular applications in the modern day washing machines. A washing machine of 8 kgs capacity was able to operate its motor within the speed range from 200 rpm to 1,200 rpm. In this case, the sale of variable-frequency washing machines improved by 35%.
In an irrigation system, a 15-kilowatt water pump using an AC motor’s speed regulation function can increase flow during peak water usage and reduce energy consumption during non-peak periods. This optimization can save at least 50,000 yuan in electricity bills annually.
An electric bus uses an AC motor with real-time adjustment of the output power and speed according to road conditions. It gains torque when climbing uphill and recovers energy when driving downhill. Electric buses with adjustable-speed AC motors consume 20% less energy than vehicles with fixed-speed motors.
Compact and Efficient
The power density of a three-phase asynchronous motor is usually 0.2 to 1 kW/kg. Even with a weight of only 5 kg, it can provide up to 5 kW of output power. In contrast, a DC motor of the same power may weigh more than 7 kg and be over 20% larger in volume.
A vacuum cleaner fitted with an AC motor weighs just 800 grams and is 30% smaller in volume. For household appliances, compact and easy-to-store merchandise is preferred by over 80% of consumers.
For an automated production line, for example, it is possible to find AC servo motors with a diameter as small as 50 mm yet with output power up to 750 watts. Compared with previous years, production lines with small-sized AC servo motors increased the unit area output rate by 15%.
An AC motor used in an electric vehicle’s drive system has a diameter of only 25 cm and weighs just 25 kg, yet it can provide a continuous output power of 100 kilowatts. More than 90% of the drive systems use compact AC motors.
The AC-motor handheld electric sander weighs only 500 grams with 40% volume shrinkage but offers up to 300 watts of output power. These tools increased work efficiency by 20%, and their annual sales have grown by 25% accordingly.
The cooling system in an MRI scanner requires an electric motor that is both efficient and compact. Its diameter is normally less than 100 mm and can achieve continuous output power up to 2 kilowatts at efficiencies up to 95%.
The 3-kilowatt AC motor used in the ventilation system has an outer diameter of only 80 mm, weighs less than 3 kilograms, but can support 1,500 cubic meters per hour of airflow. This reduces equipment installation and maintenance costs by up to 10% annually.
A small agricultural water pump with an AC motor weighs only 2 kilograms but can drive 500 liters per minute of water flow. Compact, high-efficiency motors help farmers save 30% in energy costs and reduce equipment maintenance frequency.
However, compared to the fact that a single micro-AC motor used for a satellite attitude control system weighs but 200 grams in less volume than 100 cubic centimeters, it already achieves operation efficiency of higher than 90%.
Durable and Stable
While an average life of a standard AC is 15-20 years, it would extend up to 25 years with good maintenance. A DC motor has a lifespan of 10 to 15 years, which requires more maintenance and higher costs by consequence.
In industrial production, in the case of a 24-hour operation on a production line, after 5 years of operation, less than 1% of AC motors would fail. In contrast, due to the operational requirements, about 5% of DC motors will fail, which will result in a production stop. This reduces downtime by more than 300 hours a year, translating into a saving of around 2 million yuan in losses associated with the stopped production.
For an AC motor-driven washing machine, usage of 10 times a week and 2 hours of operation result in over 10,000 hours of running in 10 years. More than 85% of users are very satisfied with the durability of home appliances driven by an AC motor.
It is possible for an electric bus with an AC motor to continue running for more than 10 years, even with frequent stops and starts. The reliability rate of a 150-kilowatt AC motor stands at 99%, requiring almost no major repairs within 5 years.
AC motors can run continuously in agricultural irrigation systems for more than 5,000 hours at temperatures above 45°C. The failure rate of all other motors is 30% less than that of equipment with AC motors.
An HVAC motor used in a large commercial building can last for 20 years on average and operate at high efficiency for upwards of 5,000 hours per year. AC motors maintain efficiencies above 90% throughout much longer time frames, but the efficiency of DC motors is likely to drop as low as 80% after 5 years.
The mine ventilation AC motor can operate over 20,000 hours under high humidity and dust conditions and can save up to 20% of the equipment replacement cost, which saves over 5 million yuan.
Strong Anti-Interference
Compared with DC motors, AC motors do not have brushes and commutators, thus having less electromagnetic interference. During industrial production, the equipment using an AC motor will reduce electromagnetic interference by an average of 50%.
An air conditioner with an AC motor produces small interference to the electrical equipment around it. More than 90% of users don’t feel any impact on the stability of their TV, mobile phone, or Wi-Fi, but there was interference from similar products using DC motors 10% of the time.
The electromagnetic interference rate is less than 0.1% for an AC motor-driven production line. There is an electronic component manufacturing factory whose equipment, when working in a high-frequency electromagnetic field, normally uses an AC motor, but the probability of failure of DC motors can be as big as 5%.
MRI coolers used in medical applications should be able to operate without any interference in high magnetic fields. AC motors are stable under 3 Tesla and higher magnetic field strengths with over 99.9% stability rate, but DC motors have an 80% reliability only under the same operating conditions.
Electric cars using AC motors have less than a 0.01% chance of control system failure, while older DC motor vehicles have been known to fail at a rate as high as 0.5% of total vehicles.
For instance, in the precision irrigation systems of farm machinery, an AC motor can support up to 30 volts of grid fluctuations while keeping output stability, whereas DC motors might show power fluctuation or even cannot work under the same condition, which can reduce downtime by as much as 10%.
In the cooling systems of telecom base stations, AC motors have 40% stronger capability in resisting electromagnetic interference compared to DC motors. The replacement of more than 20,000 AC motors nationwide by a major telecom operator enhanced system reliability by 25% and reduced communication outages by up to 35%.
In HVAC systems, a 3-kilowatt AC motor can maintain an output efficiency as high as 95%, even with voltage fluctuations as large as ±10%.
It can also be applied to the aerospace sector: micro-AC motors used in attitude control systems of satellites work in high radiation environments. These can operate more than 10,000 hours at radiation intensities over 100 kilograys while DC motors operate for only up to 2,000 hours under the same conditions.
