Alternator Power System; Alternator - Cessna 1969-1976 172 Series Service Manual

16-34. REMOVAL AND INSTALLATION. @efer to
figure 16 -2. )
a. Open battery box and disconnect the ground
cable from the negative terminal of the battery and
pull the cable from the battery box.
diode board from the studs of the receptacle and
remove the battery cable.
c. Remove the s c r e w s and nuts holding the recep-
tacle. The receptacle will then be f r e e from the
bracket.
d. To install
a
ground service receptacle, r e v e r s e
this procedure. Be sure to place the ground strap on
the negative stud of the receptacle.
b. Remove the nuts, washers, ground strap and
16-35. ALTERNATOR POWER SYSTEM.
TROUBLE PROBABLE CAUSE
AMMETER INDICATES HEAVY
DISCHARGE WITH ENGINE
Shorted radio noise filter
or shorted wire.
16-36. DESCRIPTION. The alternator system con-
sists
of an engine driven alternator,
a
voltage regu-
lator mounted on the left hand side of the firewall and
a
circuit breaker located on the instrument panel.
The system is controlled by the left hand portion of
the split rocker, master switch labeled "ALT.
"
Be-
ginning with 1972 models an over-voltage sensor
switch and red warning light labeled "HIGH VOLTAGE
REMEDY
1. Remove cable from output
terminal of alternator. Check
graph 16-42). The aircraft battery supplies the
source of power for excitation of the alternator.
16-37. ALTERNATOR.
16-38. DESCRIPTION. The 60-ampere alternators
used on the 172 model a r e three phase, delta connect-
ed with integral silicon diode rectifiers. The alter-
nator is rated at
14 volts
at
60 amperes continuous
output. The moving center part of the alternator
(rotor) consists of a n axial winding with radial inter-
locking poles which surround the winding. With ex-
citation applied t o the winding through slip rings the
pole pieces assume magnetic polarity. The rotor
is mounted in bearings and rotates inside the stator
which contains the windings in which a c is generated.
The stator windings a r e three-phase, delta connected
and a r e attached to two diode plates, each of which
contain three silicon diodes.
NOT RUNNING OR ALTERNA-
TOR CIRCUIT BREAKER OPENS
WHEN MASTER SWITCH IS
TURNED ON.
-
The diode plates a r e connected to accomplish full-
wave, rectification of ac. The resulting dc output
is applied to the aircraft bus and sensed by the volt-
age regulator. The regulator controls the excitation
applied to the alternator field, thus controlling the
- -
a r e incorporated to protect the system, ( r e f e r to para-
output voltage of the alternator.
resistance from end of cable
to ground (MASTER SWITCH
MUST BE OFF). If resistance
does not indicate a direct short,
proceed to step 4. If resistance
indicates a direct short, proceed
to step 2.
2. Remove cable connections
from radio noise filter. Check
resistance from the filter input
terminal to ground. Normal in-
dication is infinite resistance.
If reading indicates a direct
short, replace filter. If no
short is evident, proceed to
step 3 .
3. Check resistance from ground
to the f r e e ends of the wires which
were connected to the radio noise
filter (or alternator i f no noise
filter is installed). Normal indica-
tion does not show
a
direct short.
I f
a
short exists in wires, repair
o r replace wiring.
16-9