Overcharging; Generator Disassembly - Ford VSG-411 Service Manual

04-I 1
Charging System
04-I 1
DIAGNOSIS AND TESTING (Continued)
If the foregoing test sequence does not identify the
cause of undercharging, it may be due to low
regulator output when the system is operating
under load.
4. Engine ON.
5. While running the engine at 1600 rpm, measure the
" F" terminal voltage. Field voltage should be 10.5 to
11.5 volts initially, and quickly taper off to 7.5 to 8.5
volts as the starting discharge is re-charged. If the
voltage is low or fluctuating, the regulator is defective.
In that case, replace the regulator.
Overcharging
If the output voltage test indicates on overcharging
condition (greater than 14.4 volts), it usually indicates a
defective regulator, but not always. If the regulator sense
voltage at the " R" terminal is lower than the output voltage
by more than 0.5 volt due to a defective diode trio, a good
regulator will increase field current and generator output in
an effort to bring the sense voltage up to regulating value.
Whether and to what extent the system will overcharge will
depend on the nature and degree of the field diode failure,
as field current must pass through the field diodes.
Generator Disassembly
If the foregoing series of on-equipment tests has not
identified the cause of charging system malfunctions,
remove and disassemble the generator for further tests.
See " Overhaul" in this section. If specialized test
equipment is available for checking diodes and stator
windings under operating-load conditions, follow the
equipment manufacturer' s instructions. If this equipment is
not available, refer the job to the nearest Authorized
Service Station.