ELECTRICAL
EQUIPMENT
(b)
Bench-testing
(i)
Removing the starting motor
from the engine
:
Disconnect the
earth
terminal on
the battery to avoid any danger of
short circuits. Remove the
heavy
cable from the starting motor.
Remove the mounting bolts and
withdraw the starting motor from
the engine.
(ii)
Measuring the Light
murning
current
:
Secure the starting motor in a
vice.
Connect the motor in series
with
a starter switch, an ammeter
capable of measuring
600
amperes
and 12-volt voltage supply. Use
cables of a similar size to those in
the vehicle motor circuit. One of
the
fixing lugs on the drive end
bracket is a suitable earthing point
on the starting motor. Connect a
voltmeter between the motor ter-
minal
and the yoke.
Operate the switch and note the
speed of armature rotation, using
a tachometer, and the readings
given by the ammeter and volt-
meter.
While the motor is running at
speed, examine the brushgear and
check
if
there
is
any undue spark-
ing at the commutator or exces-
sive brush movement.
(iv)
Fault Diagnosis
:
(iii)
Measuring lock torque
and
lock current
Fig.
15
Method of
measuring
stall
torque
and
current.
With the motor
firmly
clamped in
a vice, attach a brake arm to the
drivin pinion. Connect the free
end o
f
this arm to a spring scale.
Operate the switch and note the
current consumption, voltage and
the reading on the spring scale.
The measure of torque
can
be
calculated by multiplying the
reading on the spring scale in
pounds
by rhe length of the brake
arm in feet.
If a constant-voltage bus-bar sup-
ply is used when carrying out the
lock torque test, a higher- lock
voltage may
be
shown on the
voltmeter than the appropriate
value given in
Para.
3.
In this
event a variable resistor of suitable
current-cafiyin% capacity should
be
connected in the battery circuit
and adjusted
until
the lock voltage
is the same as that given inPara.
3.
Take
readings
of current and
torque at
this
value.
An
indication of the nature of the fault or faults may
be
deduced from the results of the
no load and lock torque tests.
SYMPTOM PROBABLE FAULT
Speed, torque and current consumption
I
Assume motor to be in normal operadog
correct.
condition.
To Next Page
Loading...
