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26-SI ALTERNATOR
1G/287 4/96
PAGE
PRODUCT INFORMATION AND SERVICE MANUAL
26-SI HEAVY DUTY BRUSHLESS ALTERNATOR
CONTENTS
INTRODUCTION
The 26-SI series alternator is a brushless, heavy-duty
integral charging system with built-in diode rectifier and
voltage regulator, producing DC current for battery
electrical systems. The 26-SI series is designed for use on
large and mid-range diesel and gasoline engines in over
the-road service, as well as for off-road, agricultural, and
construction equipment.
The 26-SI alternator may be operated in either clockwise
or counterclockwise directions (external fan may require
changing to reverse rotation) at continuous speeds of up to
10,000 alternator rpm. Intermittent speeds of up to 12,000
alternator rpm are also acceptable. The ambient temperature
range for proper operation is -34°C to +85°C (-30°F to
+185°F).
The solid state, integrated circuit voltage regulator built
into the 26-SI alternator limits system voltage by switching
the ground circuit for the rotor field on and off. When the
ground circuit is on, field current passes from a diode trio
through the stationary field coil. Nominal regulated voltages
of 13.8, 14.0, and 14.2 volts are available for 12 volt
systems, and 27.5 volts for 24-volt systems.
For 12-volt systems, an output rating of 85 amperes is
standard. For 24-volt systems, output ratings of 50 or 75
amperes are available. Refer to Figure 2 for graphs of
typical outputs over a range of alternator speeds. For
output ratings of specific 26-SI models refer to the
Specifications section of this manual.
Introduction ............................................................... 1
Features ..................................................................... 2
Operating Principles .................................................. 3
Troubleshooting ........................................................ 3
A. All Charging Systems .................................... 4
B. Systems with Indicator Light ......................... 4
C. Systems without Indicator Light.................... 5
D. R Terminal Accessory Problems ................... 5
E. No Output ....................................................... 5
F. Rated Output Check ....................................... 6
Alternator Unit Repair............................................... 7
Disassembly and Bench Checks ......................... 7
Final Disassembly............................................... 11
Alternator Assembly ................................................. 12
DE Frame and Rotor ........................................... 13
Rectifier End Housing and Components ............ 13
Final Alternator Assembly ................................. 16
Alternator Bench Test ......................................... 19
Alternator Mounting.................................................. 21
Service Parts .............................................................. 25
Alternator Specifications........................................... 26
1
Figure 2. Typical Output vs. Alternator RPM
Figure 1. 26-SI Alternator
50 amp 24V
140
120
100
80
40
20
60
1 2 3 4 5 6 7 8
RPM x 1000
A
M
P
E
R
E
S
26-5008
26-5009
75 amp 24V
85 amp 12V