Cessna T188C - Page 336

MODEL 188
& T188 SERIES
SERVICE
MANUAL
16-35.
REMOVAL AND
INSTALLATION.
(See
models
a 14-volt solid
state regulator
is installed.
figure 16-4.)
The field relay
in this regulator
is replaced
by a
a. Ensure
that master switch
is off, then
disconnect
circuit board.
The regulator
is a remove and
re-
and label
wiring
for alternator.
place item
and not
repairable
in the field.
the reg-
b.
Remove safety wire from adjusting
arm bolts and ulator
may be adjusted. Refer to Cessna
Alternator
remove bolts.
Charging
Systems Service/Parts
Manual.
c. Remove drive belt.
d. Remove
lower alternator mount bolt
and remove The voltage relay
is temperature compensated
so that
alternator.
the battery
is supplied with
the proper charging
volt-
e. Reverse
the preceding
steps for reinstallation.
age for all operating
temperatures.
With the
battery
f. After reinstallation
of the
alternator, adjust
belt fully
charged (ship's
ammeter indicating
at or
near
tension
to obtain 3/8" deflection at
the center of the zero)
and a moderate load applied to
the system (a
belt when applying
12 pounds of
pressure to the
belt. taxi
light turned on)
the voltage at
the bus bar should
After
the belt is adjusted
and the
bolt is safety wired
be within
the range shown
according
to the voltage vs
tighten the lower
support assembly
bolt to the
follow- temperature
chart
in the Cessna
Alternator Charging
ing
torque values:
Systems Service/Parts
Manual.
16-38. DESCRIPTION.-
28
VOLT. The
28 volt regu-
ALTERNATOR
LB.
-IN. TORQUE
lator
is transistorized
and controls
the alternator
output in a similar manner to a mechanical voltage
regulator
by regulating
the alternator
field current.
Shockmounted
100 to 140 The
regulation is accomplished
electronically with
the use of transistors and diodes rather than by a
vibrating armature
relay. The
voltage sensing
com-
CAUTION
ponent
is a zener
diode which
had the
characteristic
of a sudden
change in its
resistance when
a specified
Do not force
belt over pulleys.
The belt
is to
voltage is reached.
A bench
adjustment procedure
is
be installed on
the sheaves with
the arrow sym-
outlined
in the Cessna
Alternator
Charging Systems
bol
shown on the
O.D., pointing
in the direction
Service/Parts
Manual.
A Cessna Alternator
Charg-
of rotation.
This is
toward the
left or 2-4-6
side
ing
System Test
Box Assembly
(PN. 9870000-1)
is
of
the engine
when viewing
the top
of the belt.
available
through
the Cessna
Service/Parts
Center
On new aircraft
or whenever
a
new belt Is
install-
for
use in isolating
failures
in the
28-volt transistor-
ed, belt
tension should
be checked within
10 to
ized voltage
regulator (C611002-0105)
and
the 28-
25 hours
of operation.
volt Alternator.
NOTE 16-39. DESCRIPTION.- 28 VOLT, 100 AMP ALTER-
NATOR.
The regulator
is mounted
on the alternator.
When tightening
the alternator belt, apply
is transistorized,
and controls the alternator
output
pry bar pressure only to the end of the by regulating the alternator field current .
alternator
nearest
the belt
pulley.
16-40.
ADJUSTMENT.
For adjustment
of the
volt-
16-36. VOLTAGE REGULATOR. age regulator refer to Cessna Alternator Charging
Systems Service/Parts Manual.
16-37. DESCRIPTION.- 14 VOLT. The alternator
voltage regulator contains two relays. One relay is 16-41. OVER-VOLTAGE WARNING CIRCUIT
actuated by the aircraft master switch and connects (AIRCRAFT SERIAL 188-0001 THRU 18803046,
the regulator to the battery. The second relay is a 28-VOLT SYSTEM)
two- stage, voltage sensitive device which is used to
control the current applied to the field winding of the 16-42. DESCRIPTION. The over-voltage warning
alternator. When the
upper set of contacts on the
system consists of a relay
assembly and an indicator
voltage
regulator relay are closed,
full bus voltage light.
The relay is voltage sensitive,
opening the al-
is applied
to the field. This condition will
exist when ternator field
circuits and turning on a red
warning
the battery is being heavily
charged or when a very
light if excessive voltage
is present. The over-
heavy load is applied to the system. When the upper voltage relay is mounted on the lower left hand fire-
contacts open,
as the voltage begins to rise
toward wall thru aircraft
serial 18800832 and on the
bulkhead
normal bus voltage, the
voltage to the alternator
forward of the instrument
panel at the center line.
field is reduced
through a resistor network
in the beginning
with aircraft serial 18800833.
base of the regulator thus reducing the output from
the alternator.
As the voltage continues to
rise, 16-43. ADJUSTMENT.
(THRU 18801997)
assuming
a very light load on the system,
the lower a. Remove
relay from the aircraft according
to the
contacts will close and ground the alternator field and following paragraph.
shut the alternator completely off. Under lightly load- b. Attach a variable, well regulated and filtered
ed conditions
the voltage relay
will vibrate between
power supply to
terminals "B"
(positive) and
"G"
the
intermediate
charge
rate and
the lower
(completely
(negative).
off) contacts. Under a moderate load, the relay will c. Adjust power supply toward 31.5 volts and listen
vibrate between the intermediate
charge rate and the
for a "click" inside the relay as
it pulls in. Note the
upper (full
output) contacts. Beginning
with 1974
voltage at which pull-in
occurs.
16-32