Cessna 150M - Testing the Battery; Charging the Battery; Battery Box; Battery Contactor

ICAUTION\
Do not add any type of "battery rejuvenator"
to the electrolyte. When acid has been spilled
from a battery, the acid balance may be ad-
justed by following instructions published by
the Association of American Battery Manufac-
turers.
16-16. TESTING THE BATTERY. The specific
gravity of the battery may be measured with a hy-
drometer to determine the state of battery charge.
If the hydrometer reading is low, slow-charge the
battery and retest. Hydrometer readings of the
electrolyte must be compensated for the tempera-
ture of the electrolyte. Some hydrometers have a
built-in thermometer and conversion chart. The
following
chart shows the battery condition for vari-
ous hydrometer readings with an electrolyte tem-
perature of 80° Fahrenheit.
BA HERY
READINGS
HYDROMETER READINGS
BATTERY
CONDITION
1. 280 Specific Gravity ............. 100% Charged
1. 250 Specific Gravity ............. 75% Charged
1. 220 Specific Gravity . . . . . . . . . . . .. 50% Charged
1. 190 Specific Gravity ............. 25% Charged
1. 160 Specific Gravity .......... Practically Dead
NOTE
All readings shown are for an electrolyte
temperature of 80° Fahrenheit. For higher
temperatures the readings will be slightly
lower. For cooler temperatures the read-
ings will be slightly higher. Some hydrome-
ters will have a built-in temperature com-
pensation chart and a thermometer. If this
type tester is used, disregard this chart.
If a specific gravity reading indicates that the battery
is not fully charged, the battery should be charged at
approximately 20 amperes for 30 minutes, or until
the battery voltage rises to 15 volts. After charging,
a load type tester will give more meaningful results.
A speCific gravity check can be used after charging
but the check cannot spot cells which short under
load, broken connectors between plates of a cell, etc.
16-17. CHARGING THE BATTERY. When the bat-
tery is to be charged, the level of the electrolyte
should be checked and adjusted by adding distilled
water to cover the tops of the internal battery plates.
Remove the battery from the aircraft and place in a
well ventilated area for charging.
16-4 Change 1
IWARNING'
When a battery is being charged, hydrogen and I
oxygen gases are generated. Accumulation of
these gases can create a hazardous explosive
condition. Always keep sparks and open flame
away from the battery. Allow unrestricted ven-
tilation of the battery area during charging.
The main pOints of consideration during a battery
charge are excessive battery temperature and violent
gaSSing. Under a reasonable rate of charge (20 am-
peres or less) the battery temperature should not
rise over 125°F, nor should gassing be so violent
that acid is blown from the vents.
16-18. BATTERY BOX.
16-19. 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.
16-20. REMOVAL AND INSTALLATION. (Refer to
figure 16-1). The battery box is riveted to mounting
brackets on the firewall. When a battery box is in-
stalled and riveted into place, all rivets and scratches
inside the box should be painted with acid-proof lac-
quer, Part No. CES1054-381, available from the
Cessna Service Parts Center.
16-21. MAINTENANCE. The battery box should be
inspected and cleaned periodically. The box and
cover should be cleaned with a strong solution of bi-
carbonate of soda (baking soda) and water. Hard de-
pOSits may be removed with a wire bursh. When all
corrosive deposits have been removed from the box,
flush it thoroughly with clean water.
IWARNING'
Do not allow acid deposits to come in contact
with skin or clothing. Serious acid burns
may result unless the affected area is washed
immediately with soap and water. Clothing
will be ruined upon contact with battery acid.
Inspect the cleaned box and cover for physical damage
and for areas lacking proper acid proofing. A badly
damaged or corroded box should be replaced. If the
box or lid require acid proofing, paint the area with
acid proof lacquer, Part No. CES1054-381, available
from the Cessna Service Parts Center.
16-22. BATTERY CONTACTOR.
16-23. 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 termi-
nal of the diode connects to the battery terminal of
the battery contactor. The small terminal of the