Section 5. Troubleshooting Model 8210/8250 Maintenance Manual
DC Electric Motors
5-8 Publication: 1146945/001, Revised: 25 Sep 2018
DC Electric Motors
DC Motor Types
• A shunt-wound motor has four external
connections: two armature (A) and two
field (E). See Figure 5-1.
Figure 5-1. Shunt-Wound Motor Circuits
motor-shunt.tif
• A compound motor, such as the lift motor,
has only two external connections because
the armature and field windings are
connected internally. See Figure 5-2.
Figure 5-2. Compound Wound Motor Circuits
motor-compound.tif
Inspection
Inspect the commutator for surface condition
and high mica. Most armatures have the mica
undercut. If the armature on your motor does
not, do not attempt to cut it.
Figure 5-3. Mica Inspection
1881_003.tif
The commutator must be smooth and clean to
provide maximum brush life. When
commutators are not correctly maintained,
carbon dust can collect in the grooves between
the segments. This can lead to a short circuit in
the armature.
Remove the brushes from their box. Inspect the
contact surface and brush length. If the brush
surface has groove(s) or pit marks, it indicates
the presence of a burr on the commutator
surface.
Good commutation is indicated by a dark
brown polished commutator and an evenly
polished brush wearing surface. See Table 5-1,
“Commutator Surfaces.”
If the commutator appears rough, pitted, or has
signs of burning or heavy arcing between the
commutator bars, remove the motor for
servicing.
Mica
Segments
NORMAL
UNDERCUT
HIGH MICA
High Mica
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