When
the
battery voltage
reaches the preset level,
the
sensing
circuit
will open the
series switching
circuit, effectively
reducing
the
field current to
zero.
Under normal load conditions the regulator will cycle on and off.
This action
will
be controlled by
the
needs
of the
system load. In other
words
--
A certain
ratio of
"On" time to
"Off"
time
will cause
the
right
amount of
average
field
current
to
flow
to maintain
the battery
voltage
at
the preset level.
The regulator
voltage is normally preset at 28,5
±0.25
volts
but
it can be readjusted by
the
user within the
range
of 26.7 to 34.0 volts
D.C.
The
Model
20138
is capable of
maintaining a 28.5
volt
system
within
±0,25
volts with changes in load from
0
amps
to
60 amps.
Oyervoltage
Protection
Circuit: The
overvoltage
protection
circuit
is designed to open the field circuit in the event
of the buss voltage rising
above the preset overvoltage
tripout
level) this
level is
normally
set at
32.0
volts
for
a 28.5 volts
system.
An
increase
of
voltage
to the preset overvoltage level
constitutes
a fault condition since
excessively
high
voltages
could damage aircraft
equipment.
In order to signal the
occurance of an overvoltage
condition,
and
the
consequent disconnection
of
the
alternator field
circuit,
a
connection
for
an "overvoltage warning"
light has been
provided. Figure
3-4
shows the basic system.
3-6
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