TP-6391 9/0850 Section 5 Component Testing and Adjustment
5.5 Slip Rings
Slip rings acquire a glossy brown finish in normal
operation. Do not attempt to maintain a bright,
newly-machined appearance on the slip rings. Cleaning
with a dry, lint-free cloth is usually sufficient. Use very
fine sandpaper (#00) and apply light pressure to remove
roughness. Do not use emery or carborundum paper or
cloth. Clean all carbon dust from the generator after
sanding the slip rings. If the rings are black or pitted,
remove the rotor and use a lathe to remove some of the
slip ring surface material.
5.6 Brushes
The brushes transfer current from the SCR module to
the slip rings. The brushes should last the life of the
generator. Abrasive dust on the slip rings, however,
shortens the life of the brushes. Excessive arcing at the
brushes could damage the SCR module and the
controller. Weak springs, damaged slip rings, sticking
brushes, a loose brush holder, or poor brush contact
causes arcing.
The brushes must be free to move within the holder and
be held i n contact with the slip rings by the springs.
When correctly positioned, spring pressure on the brush
surface c auses the brush to wear evenly. The entire
brush must ride on the ring or arcing occurs and causes
burned rings or voltage regulator failure. Figure 5-8
shows the correct positioning of the brushes. Add or
remove shims as necessary to center the brushes on
the slip rings. Replace the brushes if they show uneven
wear or are worn to one half their original length.
Check the resistance through the brushes. Resistance
through the brushes should be low, 0.1--0.2 ohms
without meter lead resistance.
TP5867
1
2
Front View
Side View
3
New 1.9 cm (0.75 in.)
4
5
6
7
8
9
2
2
3
1. Brush holder
2. Slip ring
3. Brush
4. Retainer wire
5. Shim
6. Spring
7. Brush holder
8. Correctly positioned
brush
9. Incorrectly positioned
brush
GM39685A-J
Alternator End View
Figure 5-8 Brush Assembly
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