What is Brush Holder?
Brush Holder, namely Carbon Brush Holder, acts as a mechanic guide slot for keeping the position of the Carbon Brush in the motor. Its core mission remains closely keeping the Carbon Brush through suitable pressure pressed by the spring to the Carbon Brush in order to keep sliding contact between the Carbon Brush and its rotating commutator, transmitting the stable current between the static and the rotating part of the motor.
For example, if the carbon brush just likes a pencil that keeps writing, the brush holder just likes the hand that holds the pencil, namely, it is required not only to closely hold the pencil but also to control the pressure applied while writing in order to let the pen tip that can closely contact with the paper surface.
Why we need Brush Holder?
We must understand a basic contradiction firstly, and then we can understand the function of the brush holder.
The motor is divided into two parts: the static part (the stator) and the high-speed rotating part (the rotator). If the current is needed to drive the motor to operate, it must be transmitted into its rotating rotator from its static external circuit. But the problem is that the wire cannot be directly connected to its rotating component from its static one. Once rotating, the wire will be entangled. And, the engineer will give the answer that the current will be transmitted through the sliding contact.
- Install the commutator on its rotating end (continuous current dynamo) or slip ring (AC motor and synchronous motor);
- Install carbon brush on its static end for the purpose of carbon-brush sliding on the surface of its rotating component;
- The current is transmitted to its rotating end from the static end through the sliding contact between the brush and the rotating surface.
And, the brush holder serves as the pressurization component to the carbon brush through installing and fixing. With brush holder and its carbon brush, the conductive path is formed. We can say that, without brush holder, the carbon brush cannot reliably run, which means that the motor cannot operate.
How does the brush holder work?
The operation of the brush holder can be explained three steps:
1. Locating: The carbon brush is installed into the brush holder that can limit the movement of the carbon brush within related its axial movement without swaying from side to side.
2. Pressing: The spring can push the carbon brush through its pressure finger to let the carbon brush that can be closely touch on the commutator or the surface of the slip ring with a suitable force.
3. Conducting: The current is transmitted to its rotating commutator or slip ring from its external circuit, such as the brush holder and the carbon brush, finishing the electric conduction from the static and the rotating parts.
- Too small pressure: Owing to ineffective contact between the carbon brush and the rotating surface, the followings will be generated, such as the spark, the heat and instable current;
- Too high pressure: The increasing wear speed, the carbon brush and its commutator will be heated rapidly, shortening its life time.
Therefore, the precise adjustment should be operated including the spring design of the brush holder, the gap between the brush holder and its rotating surface (the distance from the lower edge of the brush holder to its commutator or the surface of the slip ring). If too big gap, the carbon brush will easily deflective to wear its commutator; And, too small gap, the rotating surface will be scratched.
Which performances should the brush holder be required?
A qualified brush holder needs to require the following aspects:
- Keep stable carbon brush: In the process of its operation, the carbon brush is not required with swaying, beating or clamping;
- Convenient to install and remove: If checking and replacing the carbon brush, the brush holder can be easily installed and removed.
- Adjustable exposure level: The exposure level of the brush holder can be adjustable in order to avoid the wear of the commutator or the slip ring;
- Stable pressure: If the spring pressure is too less, even the fact that the carbon brush is shortened due to its wear, the pressure can still be keep its reasonable range.
- Solid structure, sound anti-wear performance, good heat dissipation and excellent electric conductivity.
Thanks to the above-mentioned advantages of the brush holder, there is a saying in the motor industry, namely, even the best carbon brushes, without improper brush holder, related performances cannot be revealed. So, we can say that the quality of the brush holder can directly affect the overall performances and its life time of the motor.
