Sunbeam ALPINE I SERIES: APLINE II SERIES, Workshop Manual

Page: 325 / 413

WSM.124
Section N (Elec. Equip.)
I
st re-issue
Page 11
CONTROL BOX
Equipment and General
We have tested and recommend the Avo Model 12
(obtainable from Avo Ltd., 92-96 Vauxhall Bridge
Road, London S.W. I.) which has been designed spe­
cially for automotive use and enables a very wide
range of checking operations to be carried out with
a single instrument.
The control box houses the generator voltage
regulator unit and the cut-out.
Although comb,ined structurally, the regulator and
cut-out are electrically separate. Both are accurately
adjusted during manufacture, and the cover pro­
tecting them should not be removed unnecessarily.
The Regulator
The regulator unit is arranged to work in conjunc­
tion with the shunt-wound generator. The regu­
lator Is set to maintain a predetermined generator
voltage at all speeds above the regulating point, the
field strength being controlled by the automatic
insertion of a resistance in the generator field cir­
cuit. When the generator voltage reaches a pre­
determined value, the magnetic field due to the
shunt or voltage winding becomes sufficiently strong
to attract the armature. This causes the contacts to
open, thereby Inserting the resistance in the field
circuit.
The consequent reduction in field current lowers
the generator voltage and this, in turn, weakens
the magnetic field due to the voltage coil. The
armature is allowed to return to its original posi­
tion, thus closing the contacts, so that the voltage
returns to the predetermined maximum. The cycle
is then repeated and the armature is set into
vibration.
As the speed of the generator rises above that at
which the regulator comes into operation the am­
plitude of vibration increases and the periods of
Interruption increase in length, with the result
that the mean value of the generator voltage under­
goes practically no increase once the operating speed
has been attained.
The series or curren_t winding provides a compen­
sation on this system of control, for if the control
were arranged entirely on the basis of voltage there
would be a risk of very seriously overloading the
generator when the battery was in a low state of
charge, particularly if the lamps were simultaneously
in use. Under these conditions, with a battery of
low internal resistance, the generator would be
forced to give an output to bring the voltage of the
system up to the same value as if the battery were
fully charged. This would necessitate an extremely
heavy current, far beyond the normal capacity of the
machine. The series winding assists the voltage coil
so that when the generator is delivering a heavy
current into a discharged battery the regulator
comes into operation at a somewhat reduced volt­
age, thus limiting the output accordingly. A split
series winding is used, the centre tapping carrying
the battery charging current while the complete
winding carries lighting and ignition loads.
By means of a temperature compensation device the
voltage characteristic of the generator is caused to
conform more closely to that of the battery under
,
F
'
D
E
.3B03
SERIES WINDINGS
Fig. 9.
Control box internal connection