PREVOST LE MIRAGE XLII BUS SHELLS User Manual

Section 6: ELECTRICAL
PA1553
41
FIGURE 27: DIODE TESTING 06071
When reinstalling diodes, torque to 9-11 lbf-ft
(12-15 Nm). Re-stake next to the threads in an
arbor press with a 1/8 inch (3,2 mm) round
punch. Press the punch with gradual pressure.
Do not strike as the shock may damage the
diodes.
7.2.2 Field Winding Check
The field winding may be checked for shorts and
opens with an ohmmeter. To check the field
winding, connect the ohmmeter to field terminal
and to ground. A resistance reading above
normal indicates an open, and a reading less
than normal indicates a short field. The normal
resistance value is 3.0 to 3.3 ohms at 80
o
F
(27
o
C). An alternate method of checking is to
place a battery of specified voltage, and an
ammeter in series with the field winding. The
current should register 7.2 to 8.3 amperes at 24
volts. Coil resistance is approximately 3.1 ohms.
Amperage readings, other than the above,
indicate an open, grounded, or shorted field. A
defective field coil can be replaced by removing
the end frame on which the field terminal is
located and then removing the four field coil
mounting screws. See FIELD REPLACEMENT”
for a detailed procedure.
7.2.3 Stator Winding Check
The stator winding may be checked for open
and short fields with an ohmmeter as follows:
Open Fields
Connect the ohmmeter leads to two pairs of
diode supports as shown in parts "A", "B", and
"C" of figure 28. Correct polarity of the leads
must be observed. The ohmmeter should
indicate a low resistance. If an infinite or a high
resistance is measured in either one or both
checks, the stator windings are open.
Ground
To check the stator windings for ground,
connect an ohmmeter to the diode support and
diode end frame as shown in part "C" of figure
28. The ohmmeter should indicate a very high or
infinite resistance. If zero or a very low
resistance is measured, the windings are
grounded.
Shorts
The stator windings are difficult to check for
shorts without finely calibrated laboratory test
equipment due to the very low resistance values
of the windings. However, if all other alternator
checks are satisfactory, yet the unit fails to
perform to specifications, shorted stator
windings are probable.
FIGURE 28: STATOR WINDING TEST 06072
7.3 DIODE REPLACEMENT
The following replacement procedures are
based on the assumption that the diode end
cover is still off and diode leads were
disconnected as explained earlier in this section.

PREVOST LE MIRAGE XLII BUS SHELLS Specifications

General

Brand	PREVOST
Model	LE MIRAGE XLII BUS SHELLS
Category	Buses
Language	English