Beechcraft 20138 - Functional Description

2-1
FUNCTIONAL
DESCRIPTION
The
Model
20138 voltage
regulator
is
designed
to control the
outputs of up
to two aircraft alternators connected
in
parallel,
a
typical useage would
be on
twin-engined
light
aircraft.
The regulator
is designed to operate in conjunction with
alternators
operating
at
a
nominal
+28.5 volts
D.C.
However,
an
easily
accessable
control can be
adjusted
to
give
a
range of buss voltages
from
+26.7
to
+34.0
volts
D.C.
The Model
20138 voltage
regulator
incorporates
an
overvoltage
protection
circuit.
This circuit is designed to disconnect
the
alternator
field
in the
event
of the buss
voltage
rising
above
a preset
level.
This
level
is preset at
the
factory to
a
nominal 32.0
volts. However, this
tripout point
can be
readjusted
by
the user within
the range of
30.5
to
33.5
volts
D.C.
This
adjustment
is fully
covered
in Section 4
-
Adjustment
and
Maintenance.
Do
not
attempt
to
make
this adjustment
without first
reading the
CAUTION
notice
in Section 4.
In
the event
of
the
aircraft buss
voltage
rising
to the
over-
voltage
tripout
point,
(nominally
32.0
volts
D.C.)
the
overvoltage sensing
circuit
will disconnect the
alternator field
winding from
its
source
of
supply, which
will
stop
the
battery
from charging.
This
circuit
will
remain
locked
out until
the supply voltage
to the
regulator is
momentarily
interrupted.
Provision
is made for the
connection
of
an
"Overvoltage
Warning"
light. This light will
remain
on until the circuit
is
reset.
NOTE: Overvoltage
indication
constitutes a
fault
condition.
The
alternator,
regulator,
battery
system should
be carefully
examined
to
determine
the
cause of
the voltage
rise.
(See
Section
4
-
Adjustment and
Maintenance).
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