CEN N1240, N1243 Troubleshooting Guide
C.E. Niehoff & Co.
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N1240 / N1243 Alternators
Troubleshooting Guide
CONTENTS
Section 1: Wiring ................................................................2
Section 2: CAN/J1939 Diagnostics ...................................3
Section 3: Basic Troubleshooting .....................................4
Section 4: Advanced Troubleshooting .............................5
Battery Charging Conditions
The following conditions may be observed during coldstart voltage tests until temperatures of electrical system
components stabilize. The time it takes to reach optimum
voltage and amps will vary with engine speed, load, and
ambient temperature.
Maintenance/Low Maintenance Lead-Acid Battery:
Traditional lead acid batteries require lowest charge voltage of all vehicle battery chemistries. Battery cells must
be maintained by periodically topping off with distilled
water as required.
Maintenance-free Lead-Acid Battery:
Maintenance-free batteries are similar to Maintenance/
Low Maintenance batteries, but may require slightly higher
charge voltage.
Deep-cycle/Marine Maintenance-free Battery:
Charge acceptance of these batteries may display characteristics similar to maintenance-free batteries and may
charge faster due to generally lower capacity relative to
size.
AGM (Absorbed Glass Mat) Maintenance-free Battery:
These dry-cell batteries respond better than standard
maintenance-free batteries. If battery state of charge
(SOC) drops to 75% or less, batteries should be
recharged to 95% or higher separately from engine charging system to avoid damaging charging system
components and to provide best overall performance.
Charge acceptance of these batteries may display
teristics similar to maintenance batteries, but may require
higher charge voltage and will draw signicant current (<100
amps) when under 50% SOC.
Lithium Battery:
Lithium batteries have unique charging characteristics that
differ from lead acid. These batteries require charging
systems congured specically for lithium battery chemistries. Contact CEN for more information on lithium battery
charging systems and components.
charac-
Testing Guidelines
Professional service technicians rely on the following
guidelines when testing electrical components.
Voltage testing:
• Set meter to proper scale and type (AC or DC).
• Be sure to zero the meter scale or identify the meter
burden by touching meter leads together. Meter burden
must be subtracted from nal reading obtained.
• Be sure the meter leads touch source area only.
Prevent short circuit damage to test leads or source by
not allowing meter leads to touch other pins or exposed
wires in test area.
• Be sure to use CEN tools designed especially for troubleshooting CEN alternators when available.
Resistance (ohm) testing:
• Set meter to proper scale.
• Be sure to zero the meter scale or identify the meter
burden by touching meter leads together. Meter burden
must be subtracted from nal reading obtained.
• Be sure meter leads touch source area only. Allowing
ngers or body parts to touch meter leads or source
during reading may alter reading.
• Be sure reading is taken when source is at 70ºF. Readings taken at higher temperatures will increase the
reading. Conversely, readings taken at lower temperatures will decrease the reading.
• Be sure to test directly at the source. Testing through
extended harnesses or cable extensions may increase
the reading.
• "OL" as referenced in this document refers to open cir-
cuit: "innite" resistance, typically in very high kilo- or
megaohm range depending on meter and settings.
Diode testing:
• Diodes allow current to ow in one direction only. Typical voltage drop in forward bias can range from 0.1-
0.85V. Meter should read OL in reverse bias. Check
meter user manual for meter-specic testing guidelines.
Voltage drop testing:
• Measure voltage between B+ on alternator or power
source and B- (ground) on alternator or source. Record
reading. Move to batteries or other power source and
measure again between B+ and B- terminals on battery
or other power source. The difference between the two
readings represents voltage lost within circuit due to,
but not limited to, inadequate cable gauge or faulty connections.
• Voltage drop measurements must be taken with all electrical loads or source operating.
Dynamic/Live testing (Connecting power and ground to
component to test operation/function out of circuit):
• Connect jumper leads directly and securely to power
source contacts of component being tested.
• Make any connection to power and ground at power
supply or battery source terminals. Do not make connection at component source terminals, as that may
create an arc and damage component source terminals.
Page 1TG40B
Section 1: Wiring Diagram
Section 1: Wiring Diagram
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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-conducting 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 gradually 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.
(next to regulator connector)
Figure 1 — N1240-3/N1243-2 Alternators and
B+ terminal
TT
T
TT
TT
T
TT
B–
terminal
N3218 Regulator Terminals
IGN terminal
TT
T
TT
Page 2
Page 2
Figure 2 — N1240-3/N1243-2 Alternators with N3218 Regulator
TG0040A
TG40B
Section 2: CAN/J1939 Diagnostics
Section 2: CAN/J1939 Diagnostics
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CAN/J1939 Interface
DESCRIPTION AND OPERATION
The CEN N3218 digital regulator is compatible with
SAE J1939 communications standard for vehicle
networking.
CEN uses MIL-STD connector MS3112E12-10P to
interface between the N3218 and the vehicle J1939
databus and battery box sensors. Mating connector is
MS3116E12-10S or equivalent. If this connection is
not used, it must be sealed with connector cover
MS3181-12CA or equivalent. Connector pinout is
shown in Table 1. Message content is shown in Table 2.
Battery box sensing inputs connect to battery pack
positive terminal (pin J) and battery box thermistor
(pin H). Thermistor is 10K NTC with 32650Ω at 0ºC,
10000Ω at 25ºC, 3601Ω at 50ºC and 1% interchangeability. Thermistor location should be chosen
so that it closely represents battery case temperature. Thermistor connects between pin H and vehicle
chassis, battery pack negative terminal, or negative
bus bar. If either sensing input (pin H or J) is not
used, regulator will default to internal temperature
and alternator voltage.
TABLE 1 – J1939 Connector
Circuit Identification
Pin
A
B
C
D
E
F
G
H
J
K
Identification
J1939+
J1939–
J1939/SHLD
B–/GND
Mfr use only
Mfr use only
Mfr use only
Ext. Temp. Sense
Ext. Voltage Sense
unused
Figure 3 – J1939
Connector Pins
TABLE 2 – N3218 Regulator/J1939 Readout Diagnostics (see Table 3)
Regulator Readout
Alternator Speed
Alternator Voltage
Battery Voltage
Regulator Temp.
Alternator Current
Alternator Load
Battery Temp.
Stator Voltages
Expected Reading
1500 to 8000 RPM
26 to 30 V (when charging)
26 to 30 V (when charging)
–40 to 125ºC
0 to 300 A
0 to 100%
–40 to 80ºC
10 to 18 V (when charging)
Table 3 — Message Data
PGN Name 1 (1) 2 3 4 5 6 7 8
FED5 Alt. Speed Alt. Speed
FEF7 Alt. Voltage Alt. Voltage Batt. Voltage
FEA7 Alt. Temp. Reg. Temp.
FFC8 Proprietary #1 Alt. Current
FFC9 Proprietary #2
FFCA Proprietary #3 Stator 1 Voltage Stator 2 Voltage
Notes:
(1) Byte 1 broadcast closest to CAN frame ID.
(2) Contact C. E. Niehoff & Co. for definition of custom proprietary message content.
(2) (2)
(2) (2)
OVCO Count
Action If Expected Reading Not Present
Check belts and pulley.
Check alternator drive and regulator IGN signal.
Check battery box voltage sense signal.
Check regulator.
Check alternator output cabling.
Check alternator output cabling.
Check battery box thermistor.
Check alternator belts and output.
Alt. Hrs. Load Batt. Temp.
(2) (2) (2) (2) (2)
TG0040A
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