Textron Cessna 172R, Pilot Operating Handbook

Page: 255 / 500

CESSNA
MODEL 172R
SECTION
7
AIRPLANE
&
SYSTEMS
DESCRIPTION
LOW VOLTAGE
ANNUNCIATION
The low voltage warning annunciator is incorporated in
the
I
annunciator panel and activates when
voltage falls below
24.5 volts.
|
If
low voltage is detected,
the red annunciation VOLTS will flash
for
approximately
10
seconds
before illuminating steadily. The pilot
cannot turn off the annunciator.
In the
event
an
overvoltage condition occurs, the alternator
control unit automatically opens
the ALT FLD circuit
breaker,!
removing alternator field
current and shutting off the alternator. The
I
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 annunciator
will
illuminate when
system
voltage drops below normal. The alternator
control unit may be
reset
by resetting the circuit breaker.
If the low
voltage warning annunciator extinguishes,
normal alternator
charging has resumed; however,
if
the annunciator illuminates
again, a malfunction has occurred, and
the flight should be
terminated as soon as practical.
NOTE
Illumination
of the low voltage annunciator and
ammeter
|
discharge 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.
CIRCUIT BREAKERS AND FUSES
All circuit breakers inside the airplane are
of the "push
to reset"
or
“switch/breaker”
type.
The power distribution module
(J-Box)
uses either "push to reset" circuit breakers or spade
type
(automotive style) fuses. One glass type fuse is also used
to
provide
power
to the clock.
On aircraft using spade
type
fuses in the power distribution
module (J-Box), a spare fuse is
also
included. If the spare fuse is
used,
a
replacement
spare
should be obtained and reinstalled
before the
next
flight.
Revision 7
7-35
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