What is a DC Brush Motor

Jiaming CaiApril 3, 2023

A brushed DC motor is a motor that uses brushes and a commutator to convert electrical energy into mechanical energy. Because of the mature design of DC brush motors, low cost, and high cost performance, they are widely used in the field of micro drives. In this article, we will share the basic knowledge of DC motors ( What is a DC motor and How to choose a suitable DC motor )

Working Principle of DC Brushed Motor

Basic components: DC brushed motor consists of several basic components, including shell assembly (iron shell and magnet), rotor assembly (commutator, enameled wire, silicon steel sheet), end cover assembly (rear end cover and carbon brush).

Magnets: According to Faraday’s law, an electric current cutting the magnetic field lines of a magnet produces an Ampere force. The greater the magnetic field strength, the stronger the ampere force, and the greater the power of the motor. At this stage, the magnets on the market are mainly ferrite magnets and NdFeB magnets. The magnetic field strength of NdFeB magnets is much greater than that of ferrite magnets, but the price of NdFeB magnets is also much higher than that of ferrite magnets. Therefore, the selection of the appropriate magnet in the design of the motor depends on the power of the application.

Commutator and Brushes: The commutator is a split ring assembly mounted on the rotor shaft. The brushes are the stationary parts that make contact with the commutator as the rotor turns. The commutator works with the brushes to transmit electrical energy to the rotor. When current is applied to the stator, the resulting magnetic field causes the rotor to turn. As the rotor turns, the brushes make contact with different parts of the commutator, thereby changing the direction of the current flowing through the rotor. This change in direction of the current causes the rotor to continue spinning, allowing the motor to convert electrical energy into mechanical energy. However brushless dc motor will use electronically controlled commutation, so the life and efficiency of brushless motors will be greater than ordinary brushed motors.

How to Calculate the Power of DC Motor

Firstly , we have to know the input Power of DC Motor. The input power of the motor can be regarded as the input power of the power supply ： P = U * I

U = input voltage, I = circuit current

The power loss of the motor is approximately equal to the heating power of the circuit P （loss） = I ² * R

R = resistance

The output power of the motor is the output power of the mechanical energy of the motor: P （ output ）= E * I

E = electromotive force of the circuit = KN⌀ N= rpm of motor ⌀ = magnetic flux

Hence, P ( output ) = E * I = KN⌀I

How to Choose dc motor ( 10W examples )

Selecting the right size motor for your application requires specialized knowledge. Take a rated input voltage of 24V and a rated output power of 10 W as an example.

Although the three motors have the same rated power, they have different sizes and different rpm.

The small-sized DC 395 motor needs a rated speed of 9000 to output 10W of power. The large-volume DC 775 motor only needs a rated speed of 3000 to achieve the same power.

More Rpm = Less lifetime / more noise

So we need to choose the appropriate size motor according to the requirements of the application space.

How to Test DC Brush Motor

We are equipped with special DC motor dynamometer equipment. Install the motor on a custom-made fixture, let the motor start without load, and the dynamometer will slowly increase the load torque on the shaft end of the motor, and record the current, speed and power of the motor under different load conditions. To get a complete motor dynamometer report.

Noise Test of DC Brush Motor

The noise test standard of the DC motor is in a quiet room, at a distance of 30cm, and the data tested by the decibel meter is the standard noise data.