Troubleshooting
Aircraft Charging Systems
(Alternators/Reciprocating Engines)
by
Herb Spenner
Troubleshooting Steps
1.
2.
3.
4.
Setup
Connections
Electrical Components
Finish Up
Setup
• Avionic must be turned off
– Protects them from damage
• Master switch – On – when checking voltage
• Master switch – Off – when checking
resistance
• Select multi-meter range before measuring
• Secure item before running engine
Connections
• Check circuit breakers
– If tripped, find out why
– Remind customer of Special Airworthiness
Information Bulletin (SIAB) CE 11-10
• Electrical: Fire Hazard in Resetting Circuit Breakers
• Check grounding straps
– Refer to AC 43.13-1B – 11-188
– Use Low Ohm Meter (LMO) to check connections
• Standard multi-meter not sensitive enough
• See Practical Low Resistance Measurement – Bob
Neckolls
Connections
•
•
•
•
Check all mechanical connections are tight
Cleanup all corrosion
Check for damaged insulation
Recommend customer replace old aluminum
battery cable
– Better cold starts
– Save money through longer component life
• Check alternator belt
• Insure alternator bearings work smoothly
Typical Charging System
Power Bus Bar
Alt Fld
Alt Fld
Breaker
Main
Switch
Black
Main
Solenoid
Shunt
Resister
Orange
+
Alt
Switch
-
LO/OV
Light
Alt Out
Breaker
Amp
Mete
r
Red
Over
Voltage
Sensor
Alt Out
Battery
B
I
S
Voltage
Regulator/
ACU
A
F
F
ALT
Electrical Components
• Voltage Testing Setup (Voltage On)
– Master switch (Bat & Alt) - On
– Alternator field switch – On
– Alternator field and Main alternator breaker – On
– To generate a load, turn landing lights on
• Check Amp Meter with load on
– If needle deflects, it is OK
– If no deflection plus voltage on connections and
shunt resistor, replace meter
Voltage Regulator
• With Voltage On, check voltage regulator pins
– All pins should be close to Power Bus Bar voltage
• If Pin S is low, check Over Voltage Sensor (OVS)
connections
– If OVS connections are good, OVS is bad
• If Pin F is low
– Disconnect Pin F to alternator lead
– If Pin F is still low, replace Voltage Regulator
• Regulator is shorted, also check if alternator field
shorted
– If Pin F is high, check alternator
Voltage Regulator
• If Pin A is low
– Usually a connection problem
• If Pin I is high and LV/OV light is out
– Check bulb and wiring
Alternator
• Disconnect alternator leads and check
alternator – voltage off
• Check resistance between F (field lead) and
ground connection
– Range – 3 to 6 ohms
– If low, field coil is shorted - replace alternator
– If high
• Service brushes and clean commutator
• Resistance still high, field coil is broken - replace
alternator
Alternator
• Check for open Stator by measuring resistance
between B (battery lead) and ground
– If high, stator is open and alternator needs to be
replaced
• Check for shorted diode bridge
– Place a multi-meter in series with alternator B
lead to measure leakage current
– If leakage current is over 0.5 ma, bridge is bad –
replace alternator
Alternator
• Check for open diode bridge
– Power on, engine at 1500 RPM and lights on
– Check AC voltage on B lead
• If over 0.5 V, bridge is bad – replace alternator
Alternator
• Check alternator output
– Install multi-meter to measure current in to F lead
– If current is 3.5 A or higher and alternator output
is still low, replace alternator
• If still unable to determine problem, run
external regulator test outlined in Alternator
Test Regulator handout
Finish Up
• Do a final complete system test with engine
running and lights on
• Charge/test battery
– Remember Diamond DA42 crash
• Reinstall and tighten all components
• Clean aircraft
– Return aircraft in as-good or better shape than
you received it
• Complete logbook entry and work order
Troubleshooting Steps
1.
2.
3.
4.
Setup
Connections
Electrical Components
Finish Up
Topic
• Solid State Voltage Regulators and Alternators
– Most common solution
– Piston engine
• Not covered (because of time limitations)
– Battery problems
– Generators
– Mechanical regulators
– Turbine charging systems
– Rebuild alternator