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5) If a change from the average motor data is identified, test each coil individually and
compare the data from like coils to all of the other like coils. All of the data from like coils
should be the same. Any coil that deviates from the average values of the other coils
should be suspect.
To ease the process for DC motor testing, AT7P provides the capability to test several different
DC motor types. DC motors can be tested remotely from the DC drive or directly at the motor.
DC Motor Leads Labeling
The motor leads connected to the brushes that provide power to the armature are labeled A1 &
A2. The series field leads are normally labeled S1 & S2, shunt field leads are labeled F1 & F2.
Some motors such as dual voltage motors have additional shunt field windings which are
normally labeled as F3 & F4.
Note: One of the most common maintenance problems associated with DC motors is carbon
build up in the armature windings. AT7P readings identify these problems with inconsistent
results in back to back measurements. It is good practice to always re-measure any readings that
include the armature coils. If back to back measurements are made and the AT7P readings
change between tests, then carbon build-up is likely the cause.
DC Motor Testing from the Motor Drive
Due to the ease of accessibility of the motor leads, it is recommended to test DC motors from
motor drive for predictive maintenance testing or initial troubleshooting motor or drive faults.
This coincides with the main purpose of the detection phase of the predictive maintenance
process, which is to identify “bad” motors by observing changes in the motors condition. To do
this, it is recommended to survey as many motors as possible and test as much of the machine
as rapidly as possible. Testing from the DC motor drive actually tests multiple coils at the same
time. It tests not only the motor leads but also the motor systems cabling and other
components and connections of the motor circuit. On the other hand, the DF and capacitance
measurements must be taken directly at the motor.
If a change in the motors condition is “detected” during the motor drive test it is then
recommended to perform the test directly at the motor.
The following is a list of configurations for tests from DC drive.
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