N1240/N1243 Series Troubleshooting Guide
for N1240-3/N1243-2 Alternators
Hazard Definitions
These terms are used to bring attention to presence of hazards
of various risk levels or to important information concerning
product life.
CAUTION
NOTICE
Indicates presence of hazards that
will or can cause minor personal
injury or property damage if
ignored.
Indicates special instructions on
installation, operation or maintenance that are important but not
related to personal injury hazards.
Table of Contents
Section 1: Wiring .........................................................2
Section 2: CAN/J1939 Diagnostics .............................. 3
Section 3: Basic Troubleshooting ................................ 4
Section 4: Advanced Troubleshooting ......................... 5
Battery Conditions
NOTICE
• Maintenance or low maintenance battery:
— Immediately after engine starts, system volts are
lower than regulator setpoint with medium amps.
— 3-5 Minutes into charge cycle, system volts are
higher and amps are dropping.
— 5-10 Minutes into charge cycle, system volts are
at, or nearly at, regulator setpoint and amps are
reduced to a minimum.
— Low maintenance battery has same characteris-
tics with slightly longer recharge times.
• Maintenance-free battery:
— Immediately after engine start, system volts
are lower than regulator setpoint with low
charging amps.
— 15-30 minutes into charge cycle, volts and amps
are still low.
— 15-30 minutes into charge cycle, volts increase
several tenths. Amps increase gradually, then
quickly, to medium to high amps.
— 20-35 minutes into charge cycle, volts increase
to setpoint and amps decrease.
• High-cycle maintenance-free battery:
— These batteries respond better than standard
maintenance-free. Charge acceptance of these
batteries may display characteristics similar to
maintenance batteries.
Until temperatures of electrical
system components stabilize, these
conditions may be observed during
cold start voltage tests.
Charge Volt and Amp Values
The volt and amp levels are a function of the battery
state of charge. If batteries are in a state of discharge,
as after extended cranking time to start the engine, the
system volts, when measured after the engine is started
will be lower than the regulator setpoint and the system
amps will be high. This is a normal condition for the
charging system. The measured values of system volts
and amps will depend on the level of battery discharge.
In other words, the greater the battery discharge level,
the lower the system volts and higher the system amps
will be. The volt and amp readings will change, system
volts reading will increase up to regulator setpoint and
the system amps will decrease to low level (depending
on other loads) as the batteries recover and become
fully charged.
• Low Amps: A minimum or lowest charging system
amp value required to maintain battery state of
charge, obtained when testing the charging system
with a fully charged battery and no other loads
applied. This value will vary with battery type.
• Medium Amps: A system amps value which can
cause the battery temperature to rise above the
adequate charging temperature within 4-8 hours of
charge time. To prevent battery damage, the charge
amps should be reduced when battery temperature
rises. Check battery manufacturer’s recommendations for proper rates of charge amps.
• High Amps: A system amps value which can cause
the battery temperature to rise above adequate
charging temperature within 2-3 hours. To prevent
battery damage, the charge amps should be reduced
when the battery temperature rises. Check battery
manufacturer’s recommendations for proper rates
of charge amps.
• Battery Voltage: Steady-state voltage value as
measured with battery in open circuit with no
battery load. This value relates to battery state of
charge.
• Charge Voltage: A voltage value obtained when the
charging system is operating. This value will be
higher than battery voltage and must never exceed
the regulator voltage setpoint.
• B+ Voltage: A voltage value obtained when measuring voltage at battery positive terminal or alternator
B+ terminal.
• Surface Charge: A higher than normal battery
voltage occurring when the battery is removed from
a battery charger. The surface charge must be
removed to determine true battery voltage and state
of charge.
• Significant Magnetism: A change in the strength or
intensity of a magnetic field present in the alternator
rotor shaft when the field coil is energized. The
magnetic field strength when the field coil is energized should feel stronger than when the field is not
energized.
• Voltage Droop or Sag: A normal condition which
occurs when the load demand on the alternator is
greater than rated alternator output at given rotor
shaft RPM.
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Page 1
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-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
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B–
terminal
N3218 Regulator Terminals
IGN terminal
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Page 2
Figure 2 — N1240-3/N1243-2 Alternators with N3218 Regulator
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Section 2: CAN/J1939 Diagnostics
—
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
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.
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)
(2) (2)
OVCO Count
Table 3
(2) (2)
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.
Message Data
Alt. Hrs. Load Batt. Temp.
(2) (2) (2) (2) (2)
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Page 3
Section 3: Basic Troubleshooting
A. Tools and Equipment for Job
• Digital Multimeter (DMM)
• Ammeter (digital, inductive)
• Jumper wires
B. Identification Record
List the following for proper troubleshooting:
Alternator model number ____________________
❏
Regulator model number _____________________
❏
C. Preliminary Check-out
Check symptoms in Table 4 and correct as necessary.
TABLE 4 – System Conditions
SYMPTOM
Low Voltage Output
High Voltage Output
No Voltage Output
Check: loose drive belt; low
battery state of charge.
Check: current load on system
is greater than alternator
can produce.
Check: defective wiring or poor
ground path.
Check: defective alternator
and/or regulator.
Check: defective regulator.
Check: alternator.
Check: presence of energize
signal to E terminal on
regulator.
Check: battery voltage at alter-
nator output terminal.
Check: defective alternator
and/or regulator.
ACTION
D. Basic Troubleshooting
1. Inspect charging system components
Check connections at ground cables, positive
cables, and regulator harness. Repair or replace
any damaged component before troubleshooting.
2. Inspect connections of vehicle batteries
Connections must be clean and tight.
3. Determine battery type, voltage, and state
of charge
Batteries must be all the same type for system
operation. If batteries are discharged, recharge
or replace batteries as necessary. Electrical
system cannot be properly tested unless batteries are charged 95% or higher. See page 1 for
details.
4. Connect meters to alternator
Connect red lead of DMM to alternator B+
terminal and black lead to alternator B–
terminal. Clamp inductive ammeter on B+
cable.
5. Operate vehicle
Observe charge voltage.
CAUTION
If voltage is at or below regulator setpoint, let
charging system operate for several minutes to
normalize operating temperature.
6. Observe charge volts and amps
Charge voltage should increase and charge amps
should decrease. If charge voltage does not increase within ten minutes, continue to next step.
7. Batteries are considered fully charged if charge
voltage is at regulator setpoint and charge amps
remain at lowest value for 10 minutes.
8. If charging system is not performing properly,
go to Chart 1, page 5.
TROUBLESHOOTING
Shut down vehicle and restart engine. If alternator
functions normally after restart, a “no output condition” was normal response of voltage regulator to
overvoltage condition. Inspect condition of electrical
system.
If you have reset alternator once, and electrical
system returns to normal charge voltage condition,
there may have been a one time, overvoltage spike
that caused OVCO circuit to trip.
If OVCO circuit repeats cutout a second time in short
succession and shuts off alternator field circuit, try
third restart. If OVCO circuit repeats cutout a third
time, go to Chart 1, page 5.
If charge voltage is above
33 volts, immediately shut
down system. Electrical
system damage may occur
if charging system is
allowed to operate at
excessive voltage. Go to
Table 4 at left.
Page 4
TG0040A
Section 4: Advanced Troubleshooting
Chart 1 – No Alternator Output – Quick Diagnostic
With engine running: Does battery voltage exist at alternator B+ terminal and regulator IGN terminal?
Ye s
Repair vehicle harness circuit to IGN terminal on
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With key off, engine off: Does battery voltage exist at alternator B+ terminal?
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With key off, engine off: Unplug alternator-to-regulator harness. Connect DMM on DC volt scale across pins
C and D. Does battery voltage exist?
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With DMM on resistance scale, does the field resistance between pins F and A in harness plug measure about
1.4 (±0.2) ohms?
Yes
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Set DMM to diode test. Check continuity of thermal switch and rear stator diodes: Connect red lead to pin B
in harness plug. Connect black lead to alternator B+ terminal. Meter should read one diode drop (approx.
0.6 to 0.9 V). Disconnect leads. Connect red lead to alternator B– terminal. Connect black lead to pin B.
Meter should read one diode drop (approx. 0.6 to 0.9 V).
Ye s
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Set DMM to diode test. Check continuity of front stator diodes: Connect red lead to pin H in harness plug.
Connect black lead to alternator B+ terminal. Meter should read one diode drop (approx. 0.6 to 0.9 V).
Disconnect leads. Connect red lead to alternator B– terminal. Connect black lead to pin H. Meter should read
one diode drop (approx. 0.6 to 0.9 V).
Ye s
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Go to Page 6 to continue.
regulator or B+ terminal on alternator.
Repair vehicle harness circuit to B+ terminal on alternator.
Alternator is defective.
Alternator is defective.
Alternator is defective.
Alternator is defective.
No
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No
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No
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No
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No
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No
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PIN CONNECTIONS
Pin A F–
Pin B Phase 1
Pin C GND/B–
Pin D B+
Pin E Kelvin –
Pin F F+
Pin G Kelvin +
Pin H Phase 2
Figure 4 – Alternator-to-Regulator Harness Plug
Page 5
Section 4: Advanced Troubleshooting
(CONT’D)
Chart 1 cont’d from Page 5 – No Alternator Output – Quick Diagnostic
With DMM on resistance scale: Connect red lead to pin E in harness plug. Connect black lead to alternator
B+ terminal. Meter should read 0 ohms. Change pin E to pin G. Meter should read 0 ohms.
Yes
Alternator is defective.
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Momentarily (1 sec.) jumper pin F in harness plug to alternator B+ terminal. Touch shaft with steel tool to
detect significant magnetism. Is shaft magnetized?
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Regulator is defective.
Alternator is defective.
No
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No
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Page 6
PIN CONNECTIONS
Pin A F–
Pin B Phase 1
Pin C GND/B–
Pin D B+
Pin E Kelvin –
Pin F F+
Pin G Kelvin +
Pin H Phase 2
Figure 5 – Alternator-to-Regulator Harness Plug
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Notes
TG0040A
Page 7
Notes
If you have questions about your alternator or any of these test procedures, or if you need to locate a Factory Authorized Service Distributor, please contact us at:
TEL: 800.643.4633 USA and Canada • TEL: 847.866.6030 outside USA and Canada • FAX: 847.492.1242
Page 8
C. E. Niehoff & Co.• 2021 Lee Street • Evanston, IL 60202 USA
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