Cessna 170, Service Manual

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Cessna 170 Service Manual
Electrical System
4
MAINTENANCE OF BATTERY BOX.
The battery box should be inspected and cleaned periodically. The
box and cover should be cleaned with a strong solution of baking soda and water. Hard deposits may be
removed from aluminum boxes with a wire brush. After all corrosive deposits have been removed from the
box flush it thoroughly with clean water.
Do not allow acid deposit to come in contact with skin or clothing. Serious acid burns may result unless the
affected area is washed immediately with baking soda/water solution or 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 black lacquer such as Enmar Type TT-L-54 or Randolph Acid-Proof #345 (also meets Mil
Spec TT-L-54.)
REMOVAL AND REPLACEMENT OF BATTERY SOLENOID
.
a. Open battery box and disconnect ground cable from negative battery terminal. Pull cable clear of battery
box.
b. Remove the nut, lock washer and the two plain washers securing the battery cables to the battery
solenoid.
c. Remove the nut, lock washer 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 solenoid to the battery case. The
solenoid will now be free for removal.
e. To replace a battery solenoid, reverse this procedure.
REMOVAL AND REPLACEMENT OF GROUND SERVICE RECEPTACLE .
a. Open battery box and disconnect the ground cable from the negative terminal of the battery and pull the
cable from the battery box.
b. Remove the nuts and washers from the studs of the receptacle and remove the battery cable.
c. Remove the screws and nuts holding the receptacle and the ground strap will then be free from the
bracket.
d. To install a ground service receptacle, reverse this procedure. Be sure to place the ground strap on the
negative stud.
GENERATOR POWER SYSTEM.
The generator power system consists of the generator, voltage regulator and master switch. The generator
output is controlled by the voltage regulator to compensate for the amount of electrical power being
consumed and the condition of the battery. The master switch allows the pilot to shut the generator off
completely. An alternative method to disable the generator is to pull the generator fuse or circuit breaker.
A 12-ampere generator system is standard equipment. A 20, 25, or a 35-ampere generator is optional on
these models. If additional power is needed on the 170, an alternator conversion is possible resulting in
various ratings up to 60 amperes.
GENERATOR.
Generators used on Cessna aircraft are two brush-shunt wound types with negative ground.
The generator output is controlled by the current passing thru the field winding of the generator. The field
winding is connected to the armature circuit of the generator internally and must be grounded externally (by
the regulator after passing through a master switch circuit) in order for the generator to operate. The
generator is driven by a gear train in the engine accessory case. The output is approximately 14 volts at 12,
20, 25, or 35 amperes, depending upon the particular unit. 35 ampere generators require a cooling air blast
tube supplying fresh air directly to the brush/commutator shroud and that the engine be equipped with a
dampened crankshaft.
Three electrical connections are required for the generator. Ground is provided thru the generator case and
mounting brackets. The field terminal is connected thru the master switch to the voltage regulator FieLD
terminal and the armature terminal connects directly to the voltage regulator ARMature terminal. On some
aircraft a capacitor is attached to the ARMature terminal of the generator or the regulator. The capacitor
suppresses any radio interference that might be created by the generator/regulator.