ELECTRICAL EQUIPMENT
The bi-metallic spring also compensates
for effects due to increases in resistance of
the copper windings from cold to working
values.
The Cut-out
The cut-out is an electro-magnetically
operated switch connected in the charging
circuit between the generator and the
battery. Its function is automatically to con-
nect the generator with the battery when the
voltage of the generator is sufficient to
charge the battery, and to disconnect it
when the generator is not running, or when
its voltage falls below that of the battery,
and so prevent the battery from discharging
through and possibly damaging the genera-
tor windings.
The cut-out consists of an electro-magnet
fitted with an armature which operates a
pair of contacts. The electro-magnet em-
ploys two windings, a shunt winding of
many turns of fine wire, and a series
winding of a few turns of heavier gauge
wire. The contacts are normallv held
oDen
and are closed only when the magnetic pull
of the magnet on the armature is sufficient
to overcome the tension of the adjusting
spring.
The operation of the cut-out is as follows
:
The shunt coil is connected across the
generator. When the vehicle is starting,
the speed of the engine, and thus the
voltage of the generator, rises until the
electro-magnet is sufficiently magnetised to
overcome the spring tension and close the
cut-out contacts. This completes the circuit
between the generator and the battery
through the series winding of the cut-
out and the contacts. The effect of the
charging current flowing through the cut-
out windiigs creates a magnetic field in the
same direction as that produced by the
shunt winding. This increases the mag-
netic pull on the armature so that the
contacts are firmly closed and cannot be
separated by vibration. When
the
vehicle
is stopping the speed of the generator is
decreased until the generator voltage is
lower than that of the battery. Current then
flows from the battery through the cut-out
series winding and generator in a reverse
direction to the charging current. This
reverse current through the cut-out will
produce a differential action between the
two windings and partly demagnetise the
electro-magnet. The spring, which is under
constant tension, then pulls the armature
away from the magnet and opens the cir-
cuit. The contacts opening prevent further
discharging of the battery through the
generator.
Like the regulator, operation of the cut-out
is temperature-controlled by means of
a
bi-metallic tensioning spring.
2.
SElTING
DATA
(a) Regulator
Open-circuit setting at 20°C. and
1,500 dynamo r.p.m.
:
15.6-16.2
volts.
Note
:
For ambient temperatures other
than 20°C., the following allowances
should be made to the above setting
:
For every 10°C.
(18°F.)
above
20°C., subtract 0.3 volt.
For every 10°C. below 20°C.,
add 0.3 volt.
(b)
Cut-out
Cut-in voltage
:
12.7-13.3
Drop-off voltage
:
8.5-10.0
Reverse current
:
3.5-5.0 amp.
3.
SERVICING
(a) Testing in Position to Locate Fault
in Charging Circuit
If the generator and battery are in
order, check as follows
:-
(i)
Ensure that the wiring between
battery and regulator is in order.
To do this, disconnect the wire
from the
A
terminal of the control
box and connect the end of the
wire removed to the negative
terminal of a voltmeter.
Connect the positive voltmeter
terminal to an earthing point on
the chassis. If a voltmeter reading
is given, the wiring is in order and
the regulator must be examined.
(ii)
If there is no reading, examine the
wiring between battery and con-
trol box for defective cables or
loose connections.
(iii)
Re-connect the wire to terminal
A.
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