Chuck Yung
EASA Senior Technical Support Specialist 

This is an update to articles I wrote starting in 1999 and subsequently used as part of the foundation for “Fundamentals of DC: Operation and Repair Tips” (FDC). In FDC, we included various popular methods for some tasks. This article takes a “best practice” approach, sharing the preferred method for these tasks. 

Many service centers are unable to perform full-load testing of large DC machines. The good news is that there are specific tests that can be performed on a DC motor to verify the integrity of windings, the correct relative polarity of armature to interpoles, and proper running performance. This article explains specific tests that can help ensure a motor operates properly when the motor is installed. 

This article will cover brush spacing, how to confirm the relative polarity of interpoles and armature, checking compound field polarity, setting brush neutral and some specific tests that are useful on the test panel. Each of these tests can be performed with the motor assembled.

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