The Secret to that Old Black Magic - Commutation

DC machines have been in operation for over 100 years. Engineers and technicians understand the DC motor structure and components. They also have experience in rebuilding, testing, and making performance adjustments to the DC machines. Those that truly understand commutation, the commutation zone, and the characteristics of the carbon brush are, alas, few in number. Traditionally, the lack of a visible arc has been the defining quality for good commutation - hence the term “black”. The lack of proper understanding and relatively high-level physical science involved has led to the art of achieving this condition being nicknamed “Black Magic”. It is a reference to both the brush coloration, and commutation. The purpose of this paper is to define the commutating zone and present the critical components that create the zone. An explanation of specific brush properties and their contribution to successful commutation is included.