![Cessna 170 Service Manual Download Page 14](http://html.mh-extra.com/html/cessna/170/170_service-manual_2584449014.webp)
Cessna 170 Service Manual
Electrical System
9
Battery Fully Charged, Charging Rate Low
: This is an indication of a generator and regulator that are
operating satisfactorily.
Battery Fully Charged, Charging Rate High
: This is an indication that the charging rate is not being
reduced when it should be. This condition will cause armature trouble, overheating of the generator,
regulator, and shorten life of avionics and light bulbs, and also cause excessive “boiling” of the battery
thereby shortening it’s life. Extreme cases will result in battery “boil-over” (sometimes accompanied by a
strong “sulfur” smell) and will cause corrosion due to spilled electrolyte. Run the engine at approx. 2,000
RPM and remove the wire from the regulator FieLD terminal. If the charging rate drops to zero the regulator
is at fault. If the high charging rate continues then either the generator is faulty or there is a grounded wire
within the generator-to-master-switch-to-regulator field circuit or the master switch is improperly wired or
defective.
Battery Low, Charging Rate Low
: In order to isolate this trouble the battery and its cables must first be
confirmed to be in good condition with clean connections. Run the engine at
1,500 RPM
and temporarily
ground the regulator FieLD terminal (Appdx EL, Fig EL-09, TEST 2 (Isolate Regulator)). Now increase
engine RPM to approx. 2,000 and if the charge rate now increases the trouble is with the voltage regulator.
If the charging rate remains low the trouble is either in the generator or in the wiring circuit. Generators with
rough/worn commutator or worn brushes or weak brush springs are a distinct possibility in this case. (The
Cessna 170 has a gear-driven generator, but other aircraft with belt-driven generators may also show this
symptom with loose or worn drive belts.)
The above tests are conclusive in determining whether the regulator is at fault or whether the fault lies
elsewhere. Assuming the regulator is at fault, remove it for inspection.
INSPECTING THE REGULATOR
: The regulator may be inspected in such a manner that will uncover any
trouble as you progress so that by the time the preliminary tests are made you will know whether or not to
replace or repair it and not waste valuable time making final adjustments. No equipment other than a
battery and test lamp is required for these tests. From a practical standpoint, although component parts of
regulators are available for rebuilding, the labor plus parts costs associated with rebuilding is usually not
warranted. But sometimes regulators can be returned to service with minor repairs covered under these
inspection procedures.
After removing the regulator from the aircraft, remove the regulator cover and inspect for any obvious
indication such as burned components, burned paint or smell, corroded contacts or broken solder joints.
Examine the underneath side of the regulator for obviously broken or burned resistors and damaged potting.
(Aircraft regulator resistors are usually, though not always, covered with a high temp RTV or “potting”
substance to delay the onset of corrosion. Do not remove this potting material, but if it or the resistors are
observed to be damaged then good cause exists for rejecting the regulator.
If the above steps show the regulator appears to be serviceable then the next step is to make a continuity
test of the windings and points. To check the continuity you will need a battery-powered test lamp or a volt-
ohm meter with continuity test ability (Ohmmeter or continuity mode) with test leads.
Connect one lead to the ARMature terminal of the regulator and the other to the BATtery terminal. There
Should be no continuity. Close the Reverse Current relay (the one directly connected to the BATtery
terminal) and the lamp or meter should indicate continuity. If not, then replace the regulator.
Move the test lead from the BATtery terminal and connect it directly to the regulator case. Continuity should
exist. Using the aircraft battery in series with a test lamp this connection should make the voltage regulator
contacts move. If not, replace the regulator. While the connection is still made, lightly touch the Reverse
Current Relay with your finger and the contacts should close. If not, replace the regulator.
Connect one lead of the meter or battery powered test lamp to the FieLD terminal and the other to the
regulator case. Continuity should exist, but when the Voltage Regulator Relay contacts (the ones next to the
FieLD terminal) are opened the lamp or continuity should indicate an open circuit. If not, the insulators at
the relay attachment are shorted and should be replaced. Otherwise, replace the regulator.
REGULATOR Points/Contacts CLEANING
: Regulators operate by rapidly opening and closing their
contact points as demanded by their relay coils. The points/contacts may become pitted and burned and
may be cleaned/adjusted with ordinary ignition point files or other small files/smoothing boards such as
those used by manicurists. Never use emery on generators or regulators. Using a magnifying glass, lift the
contact arms and examine the points for evidence of pitting/burning and remove it by gently filing and
Summary of Contents for 170
Page 3: ...Cessna 170 Service Manual Electrical System ELECTRICAL ...
Page 25: ...Cessna 170 Service Manual Electrical System ELECTRICAL SCHEMATIC SNs 20267 THRU 25372 ...
Page 26: ...Cessna 170 Service Manual Electrical System ELECTRICAL SCHEMATIC SNs 25373 THRU 26995 ...
Page 27: ...Cessna 170 Service Manual Electrical System ELECTRICAL SCHEMATIC SNs 26996 AND ON ...
Page 29: ...Cessna 170 Manual Electrical System ...
Page 30: ...Cessna 170 Manual Electrical System ...
Page 31: ...Cessna 170 Manual Electrical System ...
Page 32: ...Cessna 170 Manual Electrical System ...
Page 33: ...Cessna 170 Service Manual Electrical System ...
Page 34: ...Cessna 170 Service Manual Electrical System ...
Page 42: ......