Cessna 402B 1973 - Aircraft Electrical System; Battery and Alternator Switches

EI.ECTRICAI.
SYSTEM
Eleetrical
enerry is
srpplied by a
28
volt, negative-ground,
direct
current
system
powered
by a
standard
50 ampere
or one of the
optional
100 ampere
engine-driven alternators
on each engine.
A 24
volt
battery
is located in
the
left stub wing.
An
optional
external
power
receptacle
may
be installed
on the underside of the
fuselage
just
forward
of the
cabin
door. The
receptacle
accepts a
standard
exiernal
power
source
plug.
Refer
to
Figure 2-4
f.or Electrical Power Disbibution Schematic.
BAIIERY
AND
ALIERNAIOR
SWIICHES
Separate
battery
and alternator
switches, on
the
instrument
panel,
are
provided
as a
means
of
checking
for
a
malfunctioning
alternator circuit
and
to
permit
Euch a circuit
to
be
cut-off. If
an alternator
circuit
fails
or.
maUunctions,
or when one
engine is not
running,
the switch for
that
alter-
nator
should be
turned off. Operation should
be continued
on
the function-
ing
alternator using
only
necessary
electrical equipment.
If both
alterna-
tor circuits
should
maUunction,
equipment can
be
operated
at short inter-
vals and for
a limited amount
of
time on
the battery
alone.
In either
case,
a
landing
should be made
as
soon as
possible
to
check
and
repair
the
cir-
cuits.
VOLIA'IIII\AETER
A
voltammeter,
see
Figure
2-5,
located on
the eireuit breaker panel,
is
provided
to
monitor
alternator current
output,
battery
charge
or dis-
charge rate
and
bus
voltage.
A
selector switch
labeled
L ALT.
R
ALT.
BATT,
ard VOLTS
is
located
to
the
right
of
the voltammeter.
By
posi-
tioning
the
switch to
L ALT, R
ALT,
or
BATT positior5
the respective
alternator
or battery
amperage
can be
monitored.
By
positioning
the
switch to
the
VOLTS
positiorl
the
electrical
system
bus
voltage
can be
monitored.
OVERVOTIAGE
RELAY
An
overvoltage
relay
in
the electrical
system
constanily
monitors
system
voltage.
rf
voltage
exceeds
a
predetermined
maxirnum,
the
relay
wiII
open and both
alternators
will
be
disabled.
positioning
trr6
reguratoi
selector
switch from IVIATN
to
srBy
will
select
the standf;fovervoltage
relay
and
wiII reset
the
main
relay.
EIY1ERGENCY
POWER
SWITCH
-
_An
emergency
power
switch
is
provided
in
the
arternator
system
and
is located
on
the
aft
side
of the circuit
breaker
console.
The
imergency
power
switch is
used when
the
alternators
will
not
selJ excite.
phaing-
the
switch
in
the
ON
position, provides
excitation from
the
battery even
though
the
battery
is considered
to have failed,
2-19