Carbon Brushes

What do carbon brushes do? 

A carbon brush, also known as a motor brush, is a very small part of an electric motor that conducts electrical current between stationary and rotating wires within the motor/generator. Carbon brushes generally consist of one or more blocks of carbon (including copper graphite, natural graphite, electro graphite, silver graphite, bonded carbon, and pitch-bonded carbon) with one or more terminals. Carbon is used because it's a fairly good conductor of electricity while being soft enough to provide a consistent point of contact. However, this soft property means that it wears out over time, which is why the carbon brushes need to be replaced regularly. You will usually find more than one carbon brush on any motor and there are different types for different types of motors/tools. 

Types of carbon brushes 

The term "carbon brush" appeared in the history of electrical engineering with the material change from brush-like copper wire to graphite and carbon. Carbon brushes have evolved over the decades. They are still indispensable hardware for DC electric machines today. 

Carbon Brush Designs 

One Piece Solid Carbon Brushes: Solid carbon brushes are the simplest type of brush used on the simplest machines with little or no electrical and/or mechanical considerations.

Cracked HP Brushes: These carbon brushes are also known as "spring loaded" due to the attached spring used to load the carbon into the brush holder. Most of these applications are one-piece, but FHP brushes can also be split. 

Split Carbon Brushes: Split carbon brushes are constructed by assembling 2, 3 or more carbon sectors into a single unit, resulting in optimal electrical and mechanical contact. Splitting the brush allows for more electrical contact points between the brush surface and the commutator, and an evenly distributed pressure or "driveability". The coals can be held together by a riveted clip; However, in most modern applications they are glued to a rubber hardtop.