Onan MJA Series Service Manual page 111

S.REVOLVING ARMATU;REGENERATOR,
MODELS:3MJA, 4MJA and 5MJB
The revolving armature generator is used on these generating plants.
!tis a 4-pole, sell-excited generator with inherent regulation. The
generator serves as a starting motor and furnishes dc current to re­
charge the batteries during operation.
The generator field contains shunt windings and series Windings (a few
turns of heavy wire wound on the same forms as the shunt windings).
The series ';:indings act as the starting motor field. The shunt wind ­
ings are the working field, they produce the magnetic field in which
the armature turns to produce useful output.
1 ­
NOTE: Beginning Spec F, 5MJB plants use a separate automotive start ­
er rather than the series winding in the generator. To provide
fast voltage buildup, these models use an auxiliary series wind­
ing (on two of the generator field coils) which is energized by the
battery during starticg.
The gener.ator's armature contains both ac output windings and dc wind­
ings to supply the field and battery charging circuit.
The generator is mounted to the engine through the engine-to-generator
adapter and the armature is directly connected (a tapered fit) to the
crankshaft. The outboard end of the generator rides on a ball bearing
housed in the endbelL Because of its construction the generator can't
be removed as a unit.
Generator leads are marked with metal tags for identification. Lead
and terminal marking codes are noted on the plant wiring diagrams,
Sect 10.
5.1 MAINTENANCE
,I'
Normal maintenance procedures
include periodic inspection of the
armature, ball bearing, collector
•
rings and commutator, and the
brushes normally every 500
hours. In addition, the generator
should be blown clean with com­
pressed air every 1000 hours.
INSTALL BRUSHES WITH BEVELLED
TOP SLANTING DOWN TOWARD
SPRING ""OLDER
TO REMOVE BRUSH
SPRING PRESS
SPRING HOLDER
DOWN AND OUT AS
SHOWN IN BROKEN
LINES.
AS13
5.1.1 BRUSfiES. - To examine FIG 5.A _ BRUSH INSTALLATION
thebr·ushes. remove theendbell .
band and
co~er.
Replace the brushes when they wear to about 1/2 in.
long. Allbrushes must have at least a SO percent seat.
If
they don't
sand as illustrated
,in
Fig, 5. B