Negative temperature effect of carbon brushes
- Time of issue:2022-02-14 16:19:13
Generally controlled within 80°C (temperature rise of 40°C), because of the negative temperature characteristics of the carbon brush, as the temperature of the carbon brush increases, its contact resistance decreases, and it is the lowest at 80°C to 100°C.
When the temperature exceeds 100 °C, the contact resistance increases sharply, which is extremely unfavorable for the stability of the contact surface and the current sharing between the brushes.
When a carbon brush enters an abnormal state and starts to heat up, due to the negative temperature effect of the brush, the contact resistance decreases instead, so that the current flowing through the carbon brush increases, and the carbon brush becomes hotter.
Until the contact resistance drops to the lowest point and the current flowing is the largest, such a vicious circle accelerates the deterioration of the brush. This "collapse" type change causes the current flowing through the brush to be "avalanche" type redistribution,
It is possible to make the current load difference on the brushes more than 10 times. Brushes with low contact resistance will get most of the current, likely causing them to "avalanche" as well. The consequences of this chain reaction are very serious.