What is the relation of the copper loss and brush contacts with the total loss in small dc motors?

In small DC motors, the total loss can be broadly categorized into copper loss and core loss, along with other minor losses, one of which involves the brush contacts. Here’s how each one relates to the total loss:

1. Copper Loss: This is related to the resistance of the windings in the motor. When electric current flows through the windings, it encounters resistance, which leads to power being dissipated in the form of heat. This loss is proportional to the square of the current (I²R loss, where I is the current and R is the resistance) and is a significant portion of the total loss in the motor, especially under high-load conditions. As the load on the motor increases, the current through the windings increases, hence, copper loss increases.

2. Brush Contacts Loss: Brush contacts make the electrical connection between the stationary and rotating parts of the motor, enabling current to flow into the rotor windings. The friction and electrical resistance at the contact points between the brushes and the commutator result in energy being lost as heat. Additionally, the transition of brushes across commutator segments can cause sparking, further contributing to losses, albeit small compared to copper loss. This type of loss is also influenced by the quality of the brush material, the force with which the brushes are pressed against the commutator, and the current load.

3. Total Loss: The total loss in a small DC motor is the sum of all the losses,