The silent dc motor factory tells you how to improve the DC motor of electric vehicles?
1. Pay attention to the choice of electric brushes:
The brush is a sliding contact with the commutator. The composition and contact characteristics of the brush directly affect the running direction of the motor and its wear degree. The contact characteristics of the brush mainly refer to the contact pressure drop of a pair of brushes(because the contact pressure drop under the positive and negative stage brushes is not equal, so the contact pressure drop of a pair of brushes is used to evaluate) and the friction coefficient. These factors affect the contact loss(including power loss and friction loss) and wear degree between the brush and the changer during motor operation. The main factors that affect the brush contact characteristics are the circular speed, current density, and unit pressure applied to the brush. For DC motors for electric bicycles, the circular speed is not large and generally meets the requirements. The following requirements are generally proposed for the brush of this DC motor:
(1) Because electric bicycles use low-voltage power supplies, the contact pressure drop of a pair of brushes can not be large, and it should generally be below 1V, so that the power loss is small.
(2) If the user does not need to change the brush for 2 years, the brush life should be about 1500h. The life of the brush is determined by the height it allows to wear, while the allowable wear height is determined by the minimum pressure of the spring and the stability of the brush running in the brush box after the brush is short.
(3) The size of the section area of the brush shall conform to the current density allowed by the brush. The current density is too large, causing excessive heat, increasing friction coefficient, easily causing sparks, and the motor can not even run normally.
(4) The wear of the commutator should be within the allowed range, and the running noise should be small.
The issue of the pressure applied to the brush will be discussed later.
The electric brush is divided into three categories: graphite brush, electric graphite brush and metal graphite brush. Metal graphite brushes should be used for low-voltage DC motors because its pair of brushes have small contact pressure drops(usually below 1.5 V), good wear resistance, long service life, and are suitable for motors with low circular speed.
We have used two different components of the electric brush for the electric bicycle DC motor under the rated load of life test. One is a metal graphite brush that runs 700h and has a wear rate of 45 % of the allowable wear. According to this calculation, this type of motor can run 1500h before it needs to replace the brush, which can meet the user's requirement to use the brush for 2 years. The other is to use a graphite brush to run 600h. The brush has been worn out and can no longer be used. It needs to be replaced, which means that the user must send the repair station for a maximum of 1 year.
