There are times when a DC motor or generator experiences a catastrophic failure and the customer wants to know why it happened. One type of failure that seems to stimulate lively conversation is when the failure involves dramatic damage to the brushholders and commutator. The term "flashover" describes the appearance of the failure; the very name conveys an accurate mental image of the failure. The questions that arise next are predictable: "What caused this?" and "What can be done to prevent a recurrence?" Or, if the motor was recently repaired: "What did you do to my motor to cause this?!" The purpose of this article is to help you answer those questions.

A convenient incoming inspection report for basic DC motor conditions and test values.

One of the least understood parts of a DC motor is the commutator. With a little understanding and some helpful tips, commutator life can be maximized.

When servicing DC motors, one of the many tests we do to determine the condition of the commutator is to check it for loose bars. We check for loose bars by lightly tapping the face of the commutator with a very small hammer. Then we check for suspicious sounds and movement or vibration of the bars as they're struck. A loose bar will have a dull thud while tight bars will have more of a crisp "peck." You should not feel any movement of the bar with respect to adjacent bars. If the commutator is molded or riveted,it is not repairable and it should be replaced. However, V-ring commutators can be repaired.

This video shows how to adjust the brush neutral position of a DC machine to prevent sparking at the brushes at full load.

This webinar discusses specific procedures to obtain the best possible results when machining & undercutting commutators for DC machines.

General guidance for performing brush seating or comutator reprofiling in the field.

Orientación general para realizar el ajuste del asiento de las escobillas o del conmutador en el campo.