111
To avoid the alternator failure the following things are not allowed:
- engine running with the switched off storage batteries;
- disconnecting the wire conductors from the positive and negative terminals
and unmaking the plug and socket joints of the alternator and voltage regulator
with the engine running;
- checking the alternator installation by closing the jumper of the «+» and
«-» plug and socket joint lead wires of the alternator and voltage regulator with
the engine running;
- checking the alternator working order with the help of the pilot lamp or
megger;
- switching on the storage battery with the reversed polarity of its terminals
or connecting the positive terminal of the alternator with the negative one of the
storage battery;
- short-circuit of «+» and «
Ш
» terminals of the voltage regulator.
Keep the alternator clean to ensure its good working order. When checking
the alternator, refer to readings of the current indicator. At the engine average
speed the current indicator should read the charging-current value that goes
down on restoring the storage-battery charge. If the storage battery is in good
working order and charged completely, the alternator is in good working order and
level of the controlled voltage is selected properly, the current indicator pointer
should read zero.
Remove the dust from the alternator by blowing it through with compressed
air. The alternator should be repaired by an authorized repair workshop.
For checking condition of the brush assembly, remove the brush holder. Check
if the brushes slip easily in the holder. Replace the brushes, if they project above
the brush holder channel less than 5 mm. The effort of pressing the brushes to the
commutator, if the spring is compressed to 17.5 mm, is about 0.19-0.25 N (19-25 kgf).
If wear of the collector rings exceeds 0.5 mm in diameter, turn them on lathe. The
minimum permissible diameter of turning is 29.3 mm.
The ball bearings are made tight and packed with grease sufficient for their
entire service life. In case of jamming or loud noise replace the bearings.
To check the alternator on the truck, a d.c. voltmeter of at least 1.5 class of
accuracy is required. Connect the voltmeter between «+» and «-» terminals of the
alternator. The check is carried out after the storage batteries have been connected,
when the engine speed is, approximately, 2000 min
-1
. After 10 min of the engine
operation, switch on the distance light of the head lamps and check the voltmeter
readings, which should be 26.6-29.2 V.
Test the alternator on a special bench, which provides smooth change of the
alternator rotor speed to 5000 min
-1
, and has a measurement instruments of at
least 1.5 class of accuracy. The circuit diagram for bench check of the alternator is
shown in Fig. 88. If the alternator is in good working order, its parameters should
conform to the specifications.
The alternator breakdown can occur because of the rectifying unit failure. The
latter must be tested, when the alternator has been disassembled and the stator
winding is disconnected (Fig. 89).
For testing the rectifying unit, connect the storage battery to rectifying unit
terminals via a pilot lamp. For checking the «plus» diodes connected to the recti-
fying unit «plus» bus bar, connect the storage battery wire and the other wire via
the pilot lamp in sequence - to the diode terminals. For checking the «minus» di-
odes, connect the storage battery to the «minus» bar and the pilot lamp - to the
diode terminals.
