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BEECHCRAFT Sundowner
180
Section VIII
C23 (M-1285 and After)
Handling, Serv
-
Maint
(M-2355
and after) aft of the
wing. Airplanes
equipped
with a
14-volt
electrical system
require
a
power unit
set to
13.75
to
14.25
volts, while
those equipped
with
a
28-volt
electrical
system require a
setting of
27.75
to
28.25
volts.
CAUTION
On
14-volt
airplanes,
the
power
pin
for
external
power is connected
directly
to the
bat-
tery and
continually
energized.
Turn off battery
and
alternator
switches
and
all
electrical
and
avionics
switches
when
connecting
the
auxiliary
power
unit
plug.
Assure
correct
polarity
(negative
ground)
before
connecting
auxiliary
power
unit.
Turn
on
the
battery
switch
before
turning
on
the
auxiliary
power
unit.
On 28-volt airplanes, a
reverse
polarity
diode
protection
system
is between
the external
power
receptacle
and the main
bus.
With
external
power
applied, the
bus is powered.
Turn on
the
battery
switch
only, with
all other
switches
including
avionics
switches
off, when
connecting
the
auxiliary
power
unit. Assure
correct
polarity
before
connecting
external
power.
CHECKING ELECTRICAL
EQUIPMENT
Connect an
auxiliary
power
unit as
outlined above. En-
sure that the current
is
stabilized
prior to
making any
elec-
trical equipment
or
avionics
check.
CAUTION
If
the
auxiliary
power
unit
has poor voltage
regulation
or produces
voltage
transients,the
equipment
connected
to
the unit may be dam-
aged.
January,
1982
8-11
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