Cessna 188 Series Service Manual page 320

MODEL 188 & T188 SERIES SERVICE MANUAL
Inspect the cleaned box and cover for physical dam- 16-25. RADIO PROTECTION DIODE.
age and for areas lacking proper acid proofing. A
badly damaged or corroded box should be replaced.
16-26. DESCRIPTION.
A silicon diode is installed
If the box or lid require acid proofing, paint the area
across the winding of the battery contactor to sup-
with acid-proof black lacquer, part no. CES1054-381,
press the inductive "kick" created when the contactor
available from the Cessna Supply Division.
is de-energized.
The diode is shown in figure 16-2.
Reducing the inductive peak voltage flowing back onto
16-20. BATTERY CONTACTOR.
the bus system prevents possible damaging of the
transistors in any radio equipment turned on.
16-21. DESCRIPTION. The battery contactor is
bolted to the firewall adjacent to the battery box on 16-27. GROUND SERVICE RECEPTACLE.
the A188B and thru 18803721T on the battery box on
the T188C.
Beginning with T18803721T the contactor 16-28. DESCRIPTION. (See figure 16-3.)
A ground
is mounted on a bracket adjacent to the battery. The
service is offered as optional equipment to permit
contactor is a solenoid plunger type, which is actu- use of external power for cold weather starting or
ated by turning the master switch on.
When the mas- when performing lengthy electrical maintenance. A
ter switch is off, the battery is disconnected from the reverse polarity protection system is utilized where-
electrical system.
A silicon diode is used to elimi-
by ground power must pass through an external power
nate spiking of the transistorized radio equipment.
contactor to be connected to the bux. A silicon junc-
The cathode (+) terminal of the diode connects to the
tion diode is connected in series with the coil on the
battery terminal of the battery contactor. The anode
external power contactor so that if the ground power
(-) terminal of the diode connects to the same termi-
source is inadvertently connected with a reverse
nal on the contactor as the master switch wire. This
polarity, the external power contactor will not close.
places the diode directly across the contactor solenoid
This feature protects the diodes in the alternator,
coil so that inductive spikes orginating in the coil are
and other semi-conductor devices, used in the air-
clipped when the master switch is opened. Beginning
craft from possible reverse polarity damage.
with 18801069 a vented contactor is installed.
NOTE
16-22.
REMOVAL AND INSTALLATION. (See figure
16-2.)
Maintenance of the electronic installation
a. Disconnect ground cable from negative battery
cannot be performed when using external
terminal.
Pull cable clear of battery.
power. Application of external power opens
b.
Remove the nut, lockwasher and the two plain
the relay supplying voltage to the electronic
washers securing the battery cables to the battery
bux. For lengthy ground testing of electron-
contactor.
ic systems, connect a well regulated and
c.
Remove the nut, lockwasher and the two plain
filtered power supply directly to the battery
washers securing the wire which is routed to the
side of the battery contactor.
Adjust the
master switch.
supply for 14 or 28-volts, depending on 14
d.
Remove the bolt, washer and nut securing each
or 28-volt system, and close the master
side of the battery contactor to the firewall on the switch.
A188B and the battery box/bracket on the T188C.
The contactor will now be free for removal.
NOTE
e.
To replace the contactor, reverse this proce-
dure.
On Aircraft Serials 18803047 thru 18803071
refer to Cessna Single-engine Service Let-
16-23. BATTERY CONTACTOR CLOSING CIRCUIT.
ter SE78-19, dated March 27, 1978.
-16-24. DESCRIPTION.
Beginning with aircraft se- The following check, to verify the condition of the
rial 188-0318.
An inline fuse and a resistor are in-
battery, should be made after start and removal
stalled from the positive side of the battery to the of the external power source.
small lug on the ground service receptacle. (See
1. Master Switch - OFF.
figure 16-2.) When the aircraft battery is low and 2. Taxi and Landing Light Switches - ON.
an external power source is being used to start the
3. Engine RPM - REDUCE to idle.
engine, ensure that the master switch is "ON" before 4.
Master Switch - ON (with taxi and landing
disconnecting external power.
lights on).
5. Engine RPM - INCREASE to approximately
1500 RPM.
6. Ammeter and Low-Voltage Warning Light -
CHECK.
NOTE
If the ammeter does not show a charge or
the low-voltage warning light does not go
out, the battery should be removed from
the airplane and properly serviced prior
to flight.
16-16 Revision 1