Generator - Mitsubishi 4DQ50 Service Manual

that they make uniform contact with commutator over the whole surface.
3) Inspect commutator every 500Hr of run. If affected, polish clean with #400
sand paper and wipe with clean cloth wetted with gasoline. Mica pieces must
be
0.6-0.8mm below commutator surface. If out, undercut them accordingly.
6-2 A.C. Generator
Fr. bracket
Fig.3-42 Generator Section (A.C. generator)
This A.C. generator is, differently from a conventional D.C. unit, built so that the
armature is installed outside and the field is turned inside as a rotor. It features, among
others, an extremely long service life of the brushes and ability to operate at a very high
r.p.m., because the arrangement dispenses with commutators and subjects the brushes
only to a small current, while its field has very simple make-up as compared with the
armature of a D.C. generator and it is free frpm the need of commutation.
The construction of the A.C. generator is illustrated in Fig.3-42 Revolution of the
field generates a three-phse alternating current in the armature, which is rectified by
silicon diodes installed in the rear bracket and supplied at D terminal. The field circuit is
electrified at F terminal from the battery through field relay and relay, the current
running, on one part, from brush to the field coil through slip ring and on the other, to
E terminal through the other brush and slip ring. Having silicon diodes, the generator
cannot make self·starting as a D.C. unit does by residual magnetism of the field coil, so
is excited to start from the battery.
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