Maintenance Of Battery Box; Battery Contactor; Removal And Installation; Battery Contactor Closing Circuit - Cessna 1969-1976 172 Series Service Manual

When
a battery is being charged, hydrogen
and oxygen gases a r e generated. Accumula-
tion of these gases can create
a
hazardous
explosive condition. Always keep sparks
and open flame away from the battery.
Allow unrestricted ventilation of the battery
a r e a during charging.
I
The main points of consideration during
a
battery
charge a r e excessive battery temperature and violent
gassing. Test the battery with
a
hydrometer to de-
termine the amount of charge. Decrease the charging
rate or stop charging temporarily if the battery tem-
perature exceeds 125°F.
16-22. BATTERY BOX.
16-23. DESCRIPTION. The battery is completely
enclosed in
a
box which
is
painted with acid proof
paint. The box has
a
vent tube which protrudes
through the bottom of the aircraft allowing battery
gases and spilled electrolyte to escape. The battery
box is riveted to the forward side of the firewall.
16-24. REMOVAL AND INSTALLATION. (Refer to
figure 16-1. ) The battery box is riveted to mounting
brackets on the firewall. The rivets must be drilled
out to remove the box. When
a battery box is installed
and riveted into place, all rivets and scratches inside
the box should be painted with acidproof lacquer Part
No. CES1054-381, available from the Cessna Service
P a r t s Center.
16-25. MAINTENANCE OF BATTERY BOX. The
battery box should be inspected and cleaned periodi-
cally. The box and cover should be cleaned with
a
strong solution of bicarbonate of soda (baking soda)
and water. Hard deposits may be removed with
a
wire brush. When all corrosive deposits have been
removed from the box, flush
it thoroughly with clean
water.
Do not allow acid deposits t o come in contact
with skin or clothing. Serious acid burns may
result unless the affected a r e a is washed
im-
mediately with soap and water. Clothing will
be ruined upon contact with battery acid.
Inspect the cleaned box and cover for physical damage
and for a r e a s lacking proper acid proofing. A badly
damaged o r corroded box should be replaced. If the
box o r lid require acid proofing, paint the a r e a with
acid proof lacquer P a r t No. CES1054-381, available
from the Cessna Service Parts Center.
16-26. BATTERY CONTACTOR.
16-27. DESCRIPTION. The battery contactor is
bolted to the side of the battery box. The contactor
is
a plunger type contactor which is actuated by turn-
ing the master switch on. When the master switch is
off, the battery
is
disconnected from the electrical
system. A silicon diode is used to eliminate spiking
of transistorized radio equipment. The large
ter-
minal of the diode connects to the battery terminal of
the battery contactor. The small terminal of the
diode and the master switch wire connect t o the
minus terminal of the contactor coil. A nylon cover
is installed on the contactor terminals to prevent ac-
cidental short circuits. (See figure 16-1. )
16-28. REMOVAL AND INSTALLATION. (Refer to
figure 1 6 - 1 . )
from negative battery terminal. Pull cable clear of
battery box.
b. Remove the nut, lockwasher and the
two
plain
washers securing the battery cables to the battery
contactor.
c. Remove the nut, lockwasher and the
two
plain
washers securing the wire which is routed to the
master switch.
d. Remove the bolt, washer and nut securing each
side of the battery contactor to the battery box. The
contactor will now be f r e e f o r removal.
a.
Open battery box and disconnect ground cable
e. To replace the contactor, r e v e r s e this procedure.
16-29. BATTERY CONTACTOR CLOSING CIRCUIT.
16-30. DESCRIPTION. This circuit consists of
a
5 amp fuse, a
r e s i s t o r and
a
diode located on the
firewall fuse bracket adjacent to the battery. This
s e r v e s to shunt
a
small charge around the battery
contactor
so
that ground power may be used to close
the contactor when the battery is too dead to energize
the contactor by itself.
16-31. GROUND SERVICE RECEPTACLE.
16-32. DESCRIPTION. A ground service receptacle
is
offered
as
optional equipment t o permit use of ex-
ternal power for cold weather starting
o r when per-
forming lengthy electrical maintenance. A r e v e r s e
polarity protection system is utilized whereby ground
power must p a s s through an external power contactor
to be connected to the bus. A silicon junction diode
is connected in s e r i e s with the coil on the external
power contactor so that if the ground power source
is inadvertently connected with a r e v e r s e polarity,
the external power contactor will not close. This fea-
ture protects the diodes in the alternator, and other
semiconductor devices used in the airplane, from
possible reverse polarity damage.
NOTE
Maintenance of the electronic installation
cannot be performed when using external
power. Application of external power
opens the relay supplying voltage t o the
electronics bus. For lengthy ground test-
ing of electronic systems, connect
a
well
regulated and filtered power supply directly
to
the battery side of the battery contactor.
Adjust the supply for 14 volts and close the
master switch.
16-6 Change 1