MAINTENANCE MANUAL OF ENGINE
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3. Construction of the alternator--Silicon recti-
fier
Function of the rectifier: Converts the three-phase
alternating current of the stator winding into direct
current.
Composition of the rectifier of 6-diode alternator:
The three-phase full-wave bridge rectifier
circuit is formed by 6 pieces of silicon rectifier
diodes. The 6 silicon rectifier diodes are pressed
(or soldered) onto two boards insulated from each
other, respectively, of which one board is acted as
a positive board (with output terminal bolts), and
the other one is acted as a negative board and di-
rectly connected with (grounded to) the alternator
housing. Also, the rear end cover of the alternator
is acted as the negative board.
For the three diodes pressed onto the
heat-dissipating plate, their leads are the posi-
tive-positive tubes of the diode.
For the three diodes pressed onto the rear end
cover, their leads are the negative-negative tubes
of the diode.
The heat dissipating plate must be insulated from
the rear end cover, and fixed onto the rear end
cover with bolts to act as terminals for the live
cable of the alternator, which is marked as "b"
("a", "+" or "armature").
4. Construction of the alternator--Front and
rear end covers
The rear end cover is installed with a brush holder
and a brush.
Composition of the brush components: It is com-
posed of a brush, brush holder and brush spring.
Function of the brush: The power supply is con-
ducted into the excitation winding via the slip ring.
The two brushes are installed in the holes on the
brush holder, respectively, and left contact with
the slip ring with help of the spring pressure.
The brushes should contact the slip rings well; if
not, the power generation of the alternator is in-
sufficient due to excessively small field current.
The externally-mounted brush holder can be dis-
mantled and replaced outside the alternator, and is
easy to maintain.
Ground connection type of the field winding and
corresponding brush connection scheme: Inter-
nally grounded type or externally grounded type
Internally grounded alternator: It is an alternator
whose negative brush (e) of the field winding is
directly grounded to the alternator (directly con-
nected with the housing)
Externally grounded alternator: It is an alternator
whose two brushes of the field winding are insu-
lated from the housing.
The negative pole (negative brush) of the field
winding for the externally grounded alternator is
connected to the regulator, and then grounded.
Grounding pattern of the alternator
a. Internally grounded alternator.
b. Externally grounded alternator
