Generator Brush Check; Field Ground And Open Tests; Field Voltage Test - Ford VSG-411 Service Manual

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04-10
Charging System
04-10
DIAGNOSIS
AND TESTING (Continued)
3.
If battery voltage is not present, check the circuit from
the ignition switch, through the alternator field fuse (If
so equipped) to the pigtail connector for the regulator
excitation
lead. If battery voltage is present at the
yellow regulator lead, but the regulator output is low,
replace the regulator.
Generator Brush Check
If the field terminal voltage is more than 3.0 volts,
undercharging
may be caused by high resistance in the
generator field circuit, even though generator output was
increased in the regulator bypass test. Even if field circuit
resistance is normal, it may be a combination
of low field
coil resistance (due to a partially shorted coil) and high
brush resistance.
1.
Disconnect the battery ground cable at the battery.
2.
Remove the regulator housing.
3.
Remove the field wire from the field terminal.
4.
Remove the generator
brush holder assembly.
L
BRUSH ASSEMBLY
5.
Inspect the brushes for abnormal wear, damage, dirty
contact surfaces, or sticky movement.
6.
Clean and free up the brushes or replace the
assembly.
7.
While the brush holder is out, release belt tension to
allow free rotation of the rotor and clean the slip rings
with crocus cloth or fine abrasive.
Field Ground and Open Tests
This test uses an ohmmeter to check for opens or shorts to
ground in the field.
1.
Touch the meter probes to either of the slip rings and
to ground. If the meter shows continuity or low
resistance, there is a grounded condition. In that
case, replace the rotor.
2.
Measure the resistance from one slip ring to the other.
Field coil resistance should be 4 to 5 ohms. If the
ohmmeter
indicates a high resistance between the
slip rings, the field is partially open. In that case,
replace the rotor.
Field Voltage Test
With the slip rings clean, and known good brushes
installed, repeat the field excitation voltage test at the " F"
terminal.
1.
Key ON.
2.
Release belt tension to allow the rotor to spin freely.
3.
While spinning the rotor by hand to assure good
brush contact, probe the " F" terminal and observe the
voltage. If it still does not fall within the 1.5 to 3.0 volt
range, the field coil resistance is incorrect. In that
case, replace the rotor.
VOLTMETER
GENERATOR
VOLTMETER

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