Bus Bar; Master Switch; Ammeter; Battery Power System - Cessna 150 STANDARD Service Manual

16-4A. BUS BAR.
16-4B. DESCRIPTION. Electrical power for elec-
trical equipment and electrical installations is sup-
plied through a bus bar. The bus bar is mounted on
the lower side of the fuse holders through 15073961,
A1500361, F15000903 and FA1500191. On these air-
craft, Single-Engine Service Letter, SE72-34, Dated
November 17, 1972 should be complied with to pro-
vide additional protection against accidental shorting.
Beginning with 15073962, A1500362, F15000904 and
FA1500192, the bus bar is relocated to the top of the
fuse holders.
16-5. MASTER SWITCH.
16-6. DESCRIPTION. On 1969 models the operation
of the battery and alternator systems is controlled by
a master switch. The switch is a rocker type with
double-pole, single-throw contacts. The switch,
when operated, connects the battery contactor coil to
ground and the alternator field circuit to the battery,
activating the power systems. On 1970 models and
on a new master switch is utilized. This switch is a
interlocking split rocker with the battery mode on the
right hand side and the alternator mode on the left
hand side. This arrangement allows the battery to be
on the line without the alternator, however, operation
of the alternator without the battery on the line is not
possible. The sWitch is labeled "BAT" and "ALT"
below the switch and is located on the left hand side
of the switch panel.
16-7. AMMETER.
16-8. DESCRIPTION. The ammeter is connected be-
tween the battery and the aircraft bus. The meter
indicates the amount of current flowing either to or
from the battery. With a low battery and the engine
operating at cruise speed the ammeter will show the
full alternator output when all electrical equipment
is off. When the battery is fully charged and cruise
RPM is maintained with all electrical equipment off,
the ammeter will show a minimum charging rate.
16-9. BATTERY POWER SYSTEM.
16-10. BATTERY.
16-11. DESCRIPTION. The battery is 12 volts and
is approximately 25 ampere-hour capacity. The bat-
tery is mounted on the forward side of the firewall
and is equipped with non-spill filler caps.
16-12. TROUBLE SHOOTING THE BATTERY POWER SYSTEM.
TROUBLE
BATTERY WILL NOT SUPPLY
POWER TO BUS OR IS INCAP-
ABLE OF CRANKING ENGINE.
16-2 Change 1
PROBABLE CAUSE
Battery discharged.
Battery faulty.
Faulty contactor or wiring
between contactor or master
switch.
REMEDY
1.
Measure voltage at "BAT"
terminal of battery contactor
with master switch and a suit-
able load such as a taxi light
turned on. Normal battery
will indicate 11. 5 volts or
more. If voltage is low, pro-
ceed to step 2. If voltage is
normal, proceed to step 3.
2. Check fluid level in cells
and charge battery at 20 amps
for approximately 30 minutes
or until the battery voltage
rises to 15 volts. Check bat-
tery with a load type tester.
If tester indicates a good bat-
tery, the malfunction may be
assumed to be a discharged
battery.
If
the tester indicates
a faulty battery, replace the
battery.
3. Measure voltage at master
switch terminal (smallest) on
contactor with master switch
closed. Normal indication is
zero volts. If voltage reads
zero, proceed to step 4. If a
voltage reading is obtained
check wiring between contactor
and master switch. Also check
master switch.