Influence of Brush Positioning on Separately Excited DC Motor Operation

Abstract

In DC machines the brush collector system is considered to be a critical system to their operation. Improper positioning of the brushes can lead to malfunction or improper operation. This paper analyses the operation of a very low power DC motor when the brushes are placed in the geometrically neutral axis and when they can move at an angle between ± 10 ° and ± 20 ° to this axis. During motor tests, we determined the the speeds corresponding to the different brush positions, the waveforms of the supply voltage and the current in the winding of the armature were analysed, the torques for different loads of the armature were determined and the mechanical characteristics were constructed. The motor under analysis is part of a teaching test bench, therefore the strengths of the DC motor test bench with separate excitation winding were highlighted and solutions for its modernization were proposed. The analysis shows that the position of the brushes influences the speed and torque of the motor, and a proper positioning of the brushes can lead to an operation without large variations in current and torque.