ELECTRICAL
EQUIPMENT
(iv)
Fault
Diagnosis--(cont'd)
SYMPTOM
Speed, torque and current consumption low.
Speed and torque low, current consumption
hgh.
Speed and current consumption high, torque
low.
Armature does not rotate, no current con-
sumption.
Armature does not rotate, high current
consumption.
Excessive brush movement causing arcing at
commutator.
Excessive arcing at the commutator.
PROBABLE FAULT
High resistance in brushgear,
e.g.,
faulty
connections,
dirty
or burned commutator
causing bad brush contact.
Tight or worn bearings, bent shaft,
in-
suacient end play, armature fouling a pole
shoe, or cracked spigot on drive end bracket.
Short-circuited armature, earthed armature
or
short-circuited field coils.
Short-circuited field coils.
Open-circuited armature or field coils. If
the commutator is badly burned there may
be poor contact between brushes and com-
mutator.
Earthed field winding. Armature prevented
mechanically from rotating.
Low brush spring tension, worn or out-of-
round commutator.
"
Thrown
"
or high
segment on commutator.
Defective armature
windings
If any fault is indicated, the motor must be dismantled, see Para.
4
(c)
and a further
check made.
(c) Dismantling
Unscrew the terminal nuts from the
.
.
Remove the cover band, hold back the
field coil terminal post protruding
brush springs and
lift
the brushes from
from the commutator end bracket.
their holders.
Unscrew the two through bolts from
the commutator end bracket and
,-N
IXXI
UN*
S~I*C
remove the commutator end bracket
9
9
from the yoke.
Remove the driving end bracket com-
plete with armature and drive from
the starting motor yoke.
(d)
Bench Inspection
After the motor
has
been dismantled
m
WO
L"=
individual items must be examined,
Fig.
16
Showing Starter Motor
dismantled.
as
follows
:-
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