Cessna 152 - Page 126

SECTION7
CESSNA
MODEL 152
AIRPLANE
&
SYSTEMS
DESCRIPTIONS
Norm.ally,
both
sides
of
the
master
switch
should
be
used
simultane-
ously;
however,
the
BAT
side
of
the
switch
could
be
turned
ON
separately
to
check
equipment
while
on
the
ground.
The
ALT
side
of
the
switch,
when
placed
in
the
OFF
position,
removes
the
alternator
from
the
electrical
system.
With
this
switch
in
the
OFF
position,
the
entire
electrical
load
is
placed
on
the
battery.
Continued
operation
with
the
alternator
switch
in
the
OFF
position
will
reduce
battery
power
low
enough
to
open
the
battery
contactor,
remove
power
from
the
alternator
field,
and
prevent
alternator
restart.
AMMETER
The
ammeter,
located
on
the
upper
right
side
of
the
instrument
panel,
indicates
the
flow
of
current,
in
amperes,
from
the
alternator
to
the
battery
or
from
the
battery
to
the
airplane
electrical
system.
When
the
engine
is
operating
and
the
master
switch
is
turned
on,
the
ammeter
indicates
the
charging
rate
applied
to
the
battery.
In
the
event
the
alternator
is
not
functioning
or
the
electrical
load
exceeds
the
output
of
the
alternator,
the
ammeter
indicates
the
battery
discharge
rate.
ALTERNATOR CONTROL
UNIT
AND
LOW-VOLTAGE
WARNING
LIGHT
The
airplane
is
equipped
with
a
combination
alternator
regulator
high-low
voltage
control
unit
mounted
on
the
engine
side
of
the
firewall
and
a
red
warning
light,
labeled
LOW
VOLTAGE,
under
the
ammeter
on
the
instrument
panel.
·
In
the
event
an
over-voltage
condition
occurs,
the
alternator
control
unit
automatically
removes
alternator
field
current
which
shuts
down
the
alternator.
The
battery
will
then
supply
system
current
as
shown
by
a
discharge
rate
on
the
ammeter.
Under
these
conditions,
depending
on
electrical
system
load,
the
low-voltage
warning
light
will
illuminate
when
system
voltage
drops
below
normal.
The
alternator
control
unit
may
be
reset
by
turning
.the
master
switch
off
and
back
on
again.
If
the
warning
light
does
not
illuminate,
normal
alternator
charging
has
resumed;
however,
if
the
light
does
illuminate
again,
a
malfunction
has
occurred,
and
the
flight
should
be
terminated
as
soon
as
practicable.
7-24
NOTE
Illumination
of
the
low-voltage
light
and
ammeter
dis-
charge
indications
may
occur
during
low
RPM
conditions
with
an
electrical
load
on
the
system,
such
as
during
a
low
RPM
taxi.
Under
these
conditions,
the
light
will
go
out
at
higher
RPM.
The
master
switch
need
not
be
recycled
since
an
over-voltage
condition
has
not
occurred
to
de-activate
1
July
1978