Page 2
TG0040A
Section 1: Wiring Diagram
CEN N1240-3/N1243-2 Alternators
Description and Operation
N1240-3 and N1243-2
28 V 260 A alternators are
internally rectified. All windings and current-conduct-
ing components are non-moving, so there are no
brushes or slip rings to wear out.
After engine is running,
N3218
regulator receives
energize signal. Regulator monitors alternator
rotation and provides field current only when it
detects alternator shaft rotating at or above idle
speed.
After regulator detects alternator rotation, it gradu-
ally applies field current, preventing an abrupt
mechanical load on accessory drive system. The soft
start may take up to 20 seconds.
N3218
regulator used with these units also
• is negative temperature compensated. Setpoint is
28.8 ± 0.5 V at 72 F when configured to operate
with 6TMF type batteries.
• provides overvoltage cutout (OVCO). Regulator
will trip OVCO when system voltage rises above
setpoint by 3 V for longer than 3 seconds. OVCO
feature detects high voltage and reacts by opening
alternator field circuit and turning off alternator.
Restarting engine or waiting until system voltage
drops 5 V below setpoint will reset OVCO circuit.
• maintains alternator steady-state output voltage
at regulated settings as vehicle electrical loads are
switched on and off.
Figure 2 — N1240-3/N1243-2 Alternators with N3218 Regulator
Figure 1 — N1240-3/N1243-2 Alternators and
N3218 Regulator Terminals
B+ terminal
(next to regulator connector)
T
T
T
T
T
IGN terminal
B–
terminal
T T T T T
T
T
T
T
T
R
Section 1: Wiring Diagram
Page 2
TG40B
