Carbon Brushes conduct currents between stationary wires and moving parts, most commonly in rotating shafts. In order for alternators, electric generators, electric motors and other electronic apparatus to work effectively, it may be necessary to install carbon brushes.
There are three basic distinguished types of carbon brushes which include brushes with a DC current for automotive applications, brushes with an AC current for household applications and brushes with both AC and DC currents of industrial motor applications.
A commutator is a common rotary electrical switch in certain types of direct current rotating machines, which is used to reverse the current direction between the rotor and the external circuit.
Modern rotating machines with commutators use carbon brushes, which may have copper powder mixed in to improve conductivity. Carbon brushes are less prone to sparking, wear more evenly and the high resistance of a worn brush results in fewer problems due to dust collecting on the commutator segments.
Carbon brushes are currently the preferred brushes for commutators, due to the fact that they are soft. Their softness permits direct radial end-contact with the commutator without damage to the segments, allowing for easy rotor direction reversal without reorienting the brush holders.
A spring is used to maintain constant contact between the carbon brush and the commutator. The spring pushes the brush towards the commutator, until the brush is too worn to maintain steady contact with the commutator. A worn brush can be replaced by simply removing the old brush and inserting a new one.
When a commutated motor uses more power than a single carbon brush is capable of conducting, an assembly of several brush holders is mounted in parallel across the surface of the commutator.
This parallel holder distributes current evenly across all the carbon brushes and permits a careful operator to remove a bad brush and replace it with a new one, even as the machine continues to spin fully powered and under load.
To ensure optimal performance in electrical equipment, it is necessary that the carbon brushes, the brush holder and the contact surface are designed, installed and maintained properly.