In our previous article, we discussed the difference between brushed DC motor and brushless motor DC motor. In type of brushed DC motor, according to brush materials can be divided into precious metal brush and carbon brushes.
How Do I Choose Between Precious Metal and Carbon Brushes?
In the beginning stage of the project, INEED sales engineers and customers communicate brushed gear motor solutions, the customers often have many demands, such as the needs for higher current, higher torque, high lifespan, strong reliability, while taking into account lower loss, lower cost. In addition to achieving the basic electrical performance of brushed dc gear motor, selection motor materials are also very challenging. For example, the material of the gear box (powder metallurgy or CNC steel); Whether to choose ball bearings, whether to need high temperature oil and so on. First of all, the following table listed 5 difference points between precious metal brush and carbon brush.
| Item | Precious Metal Brushes | Carbon Brushes |
| Photo |  |  |
| Material | Silver Alloy like AGPD20 or AGPD50 | Graphite added with copper |
| Characteristics | Lower friction, High efficiency. Lower audible noise, Lower electromagnetic interference (EMI) | Higher friction, Higher no-load current Higher audible noise Higher electromagnetic emissions（EMI） |
| Applications | In smaller motors (It is uauslly under 13mm in diameter) Lower current application Shorter lifetime | In bigger motors (above 30mm in diameter) Higher current, frequent peak current in start-stop and reversed operation. End device request more durability, reliability, longer-lifetime. |
| Kosten | Lower cost | Higher cost |
| Lubrication | Special lubrication needed | No need |
Precious Metal Brushes
Precious metal brushes are usually made of metals such as gold, platinum or silver. Precious metal brushes are a less expensive commutation system suitable for low current density applications and offer low friction and high efficiency. When your application does not require durability, reliability, longer-lifetime or low current load during continuous operation, metal brushes are the most cost-effective solution.
Carbon Brushes
The main function of the carbon brush is to conduct electricity when rubbing with the metal parts, and it is not easy to increase the friction or sintering as the metal brush conducts friction on the metal. Carbon brushes provide more reliable performance by reducing losses from friction while maintaining electrical conductivity. Carbon brush, as a sliding contact on the motor commutator or slip ring, undertakes the role of conducting electricity and introducing current. It not only has good electrical conductivity, but also has excellent thermal conductivity and lubrication properties, and has a certain mechanical strength and the ability to inhibit reversing sparks. With the continuous development of motor technology, the application environment of carbon brush is becoming more and more diverse.
Let’s see a real case: At the project beginning, the customer does not know the difference between the two brushes, and directly chooses a low-priced metal brush. When the customer finished the reliability testing, it was found that the metal brush had been seriously worn and broken. The photo as below:
Broken Metal Brushes
After further communication, the customer informed that their application was a precision screwdriver that required a large load, low current, high torque, frequent switching, and a long service lifespan. Then we recommend the carbon brush motor with imported roller bearings. The customer was very satisfied with our high torque brushed motor after testing.
INEED Motors offers a wide selection of brushed DC micro metal gearmotor that will let you choose the optimal torque and speed for your application. these brushed DC gear motors are available in a wide range of gear ratios, motor winding, brushes, and encoder configurations.
Resource:
https://www.portescap.com/en/newsroom/blog/2023/03/brush-selection-for-brush-dc-motors
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