SECTION 7
AIRPLANE
&
SYSTEMS DESCRIPTIONS
CESSNA
MODEL 172N
interrupted and the switch will automatically move to the off position.
If
this occurs, allow the circuit breaker to cool approximately two minutes
before placing the switch in the ON position again.
If
the circuit breaker
opens again, do not reset it. The avionics power switch should be placed in
the off position prior to turning the master switch ON or off, starting the
engine, or applying an external power source, and may be utilized in place
of the individual avionics equipment switches.
AMMETER
The ammeter, located on the lower left side of the instrument panel,
indicates the amount 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, on the left side of the
instrument panel below the ammeter.
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.
7-26
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
the alternator system.
1 July 1979