N1128 Series Troubleshooting Guide
for N1128 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.
WARNING
CAUTION
NOTICE
Indicates the presence of hazards
that can cause severe personal
injury, death or substantial property
damage if ignored.
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: Component Description .............................. 2
Section 1: Start-up/Shutdown Procedures................... 2
Section 2: Wiring .........................................................3
Section 3: Basic Troubleshooting ................................ 4
Section 4: Advanced Troubleshooting ......................5-8
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: Component Description and Operation
CEN N1128 Dual Voltage Alternator Description and Operation
N1128 28 V 100 A alternator with 28 V/14 V (60 A
maximum on 14 V) is internally rectified. All windings and current-transmitting components are nonmoving, so there are no brushes or slip rings to wear
out.
After the N3212 regulator receives energize signal, it
monitors alternator rotation and provides field
current only when it detects alernator shaft rotating
at suitable 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.
N3212 regulator used with these units also
• is negative temperature compensated. Setpoints
are 28.0 ± 0.2 V and 14.0 ± 0.2 V at 75° F.
• provides overvoltage cutout (OVCO). Regulator
will trip OVCO when system voltage rises above
32 V in a 28 V system (16 V in a 14 V system) for
longer than 2 seconds. OVCO feature detects high
voltage and causes alternator field circuit to open,
turning off alternator. Restarting engine resets
OVCO circuit. If vehicle remains operating after
OVCO trip, the OVCO will automatically reset
when system voltage drops to 22 V (11 V on 14 V
side). Regulator then resumes normal operation.
• maintains alternator output voltage at regulated
settings as vehicle electrical loads are switched
on and off.
• allows 28 V only voltage operation if 14 V loads
are not used in the application and 14 V terminal
on regulator is not terminated.
• provides optional 14 V output at the regulator
14 V terminal when phase cable from alternator
is connected to regulator.
• maintains battery equalization between 28 V and
14 V if 14 V output is used.
Page 2
TG0027A
Section 2: Wiring
14 V B+ terminal
14 V
AC
IGN
Support
cable
within 5”
of
regulator
TT
T
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28V
14 V
Regulator
diagnostic
LEDs
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Figure 1 — N1128 Alternator and N3212 Regulator Terminals
B–
terminal
28 V B+
terminal
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Figure 2 — N1128 Alternator with N3212 Regulator
Page 3
Section 3: Basic Troubleshooting
A. Tools and Equipment for Job
• Digital Multimeter (DMM)
• Ammeter (digital, inductive)
• Jumper wires
If no tools are available, monitor LED code.
B. Identification Record
List the following for proper troubleshooting:
Alternator model number ____________________
❏
Regulator model number _____________________
❏
Setpoint listed on regulator ___________________
❏
TABLE 1 – System Conditions
SYMPTOM
Low Voltage Output
High Voltage Output
No Voltage Output
No 14 V 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; low regulator
setpoint.
Check: defective alternator
and/or regulator.
Check: wrong regulator.
Check: high regulator setpoint.
Check: defective regulator.
Check: alternator.
Check: presence of energize
signal.
Check: battery voltage at alter-
nator output terminal.
Check: defective alternator
and/or regulator.
Check:defective regulator.
ACTION
C. 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 28 V B+
terminal and black lead to alternator B– terminal. Clamp inductive ammeter on 28 V B+
cable.
5. Operate vehicle
Observe charge voltage.
CAUTION
or 16 V for 14 V system, immediately shut down system.
Electrical system damage may occur if charging system
is allowed to operate at excessive voltage. Go to page 8.
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 in each circuit
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 6.
If charge voltage is above
33 volts for 28 V system
Page 4
TG0027A
Section 4: Advanced Troubleshooting
N3212 Regulator
DESCRIPTION AND OPERATION
N3212 Regulator with OVCO is remote-mounted no
more than 12 incles from the alternator. Regulator
setpoint has negative temperature compensation. At
75ºF, the setting is 28.2 V for 28 V system and 14.1 V
for 14 V system.
Main diagnostic feature of N3212 regulator consists
of two bicolored (amber, green) LEDs located on the
side of the regulator. One LED indicates 28 V system
performance, the other LED indicates 14 V system
performance. The two LEDs work independently of
each other. See Table 2 for diagnostic features and
LED explanations.
OVCO (overvoltage cutout) will trip at any of the
following conditions:
• 14 V side trips at voltage higher than regulator
setpoint that exists longer than 2 seconds of
reading voltage above 16 V. OVCO feature detects
overvoltage and reacts by signaling relay in F–
alternator circuit to open. This turns off alternator (14 V LED is flashing AMBER /28 V LED is
off). OVCO circuit will reset by either:
— Restarting engine (regulator regains control of
alternator output voltage and resets OVCO)
OR
— System falling below 11 V. OVCO will auto-
matically reset.
• 28 V side trips at voltage higher than regulator
setpoint that exists longer than 2 seconds of
reading voltage above 32 V. OVCO feature detects
overvoltage and reacts by signaling relay in F–
alternator circuit to open. This turns off alternator (28 V LED is flashing AMBER / 14 V LED is
off). OVCO circuit will reset by either:
— Restarting engine (regulator regains control of
alternator output voltage and resets OVCO)
OR
— System falling below 22 V. OVCO will auto-
matically reset.
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 F– circuit, try
third restart. If OVCO circuit repeats cutout a third
time, check color of LEDs while engine is running.
28 V LED flashing AMBER / 14 V LED off—go to
Chart 4, page 8.
14 V LED flashing AMBER /28 V LED off—go to
Chart 3, page 8.
TG0027A
TABLE 2 – N3212 Regulator LED Diagnostics
N3212 LED COLOR N3212 STATUS
Off (Clear)
Flashing AMBER
(either 28 V or 14 V)
AMBER
(either 28 V or 14 V
with the other LED
off)
GREEN
(both flashing once
every 5 sec.)
Steady AMBER
GREEN
Regulator is not energized. Measure IGN terminal voltage.
If voltage is above 21 V, regulator is defective.
Respective system voltage is reading high voltage.
Alternator is shut down and is not producing power for either
voltage. 28 V side trips after 2 seconds of reading voltage
above 32 V. 14 V side trips after 2 seconds of reading voltage
above 16 V. Regulator remains in this mode until reset by
restarting engine or if system voltage drops below 22 V or 11
V, respectively. See Chart 3 on page 8 of Troubleshooting
Guide for 28V systems, Chart 4 for 14 V systems.
Regulator is energized, but waiting for AC signal from alternator.
Respective system voltage is below regulated setting or is
processing soft start (20-second delay).
Normal operation (respective system voltage is at regulated setting)
Page 5
Section 4: Advanced Troubleshooting
(CONT’D)
Chart 1 – 28 V LED Steady AMBER – No 28V Alternator Output – Test Charging Circuit
Start engine. Wait 20 seconds. Is 28 V LED steady GREEN on regulator?
Yes
TT
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TT
Regulator responded to overvoltage condition. Go to Chart 4
on page 8 to troubleshoot OVCO.
Shut off engine. With key off, engine off: Test for battery voltage at alternator 28 V B+
terminal. Does battery voltage exist?
Ye s
Check and repair wiring and battery cables as necessary.
Continue test.
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With key on, engine running: Test for battery voltage between IGN terminal on regulator and alternator
B– terminal. Does 28 V battery voltage exist?
Ye s
Repair vehicle ignition circuit wiring as necessary. Continue test.
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With key off, engine off: Remove alternator-to-regulator 4-pin harness from regulator. Test for battery
voltage across sockets D and C in harness plug. Does 28 V battery voltage exist?
Yes
No
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No
No
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No
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Alternator is defective.
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Ye s
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Ye s
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No
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Alternator is defective.
TT
No
No
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Alternator is defective.
SOCKET CONNECTIONS
Figure 3 – Alternator-to-Regulator
4-Socket Harness Plug
AF–
B Phase Signal AC
CB–
D 28 V B+
TG0027A
With DMM, check resistance across field coil. Connect red lead of DMM to socket A in alternator-to-regulator
harness plug. Connect black lead to B+ terminal on alternator. Does meter show 1.8 to 2.2 ohms?
Connect jumper wire from socket A in regulator harness plug to B– terminal on alternator.
Spark will occur. Touch steel tool to shaft to detect significant magnetism. Is shaft magnetized?
Test phase signal into regulator (AC). Set meter to diode tester:
Connect red lead of DMM to socket C of regulator harness and black
lead to socket B. Meter should show voltage drop value.
Then reverse meter lead connections. Meter should show OL (blocking).
Yes
TT
T
Regulator is defective.
TT
Page 6
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Section 4: Advanced Troubleshooting
Chart 2 – 14 V LED Solid AMBER – No 14 V Alternator Output – Test Circuit
With key off, engine off: Test for battery voltage of 14 V output terminal on regulator.
Does +14 V battery voltage exist?
(CONT’D)
Ye s
No
TT
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TT
Check and repair wiring and battery cables as necessary.
Continue test.
TT
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TT
Set DMM to diode tester. Connect red lead of DMM to socket C of regulator harness plug and black lead to each phase pin in phase harness
plug. Meter should show voltage drop value.
Then reverse meter lead connections. Meter should show OL (blocking).
Yes
TT
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Regulator is defective.
Alternator is defective.
SOCKET CONNECTIONS
No
TT
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AF–
B Phase Signal AC
CB–
D 28 V B+
TG0027A
Figure 4 – Alternator-to-Regulator 4-Socket Harness
Plug
PIN CONNECTIONS
A Phase P1
B Phase P2
C Phase P3
Figure 5 – Phase Connection 3-Pin Harness Plug
Page 7
Section 4: Advanced Troubleshooting
(CONT’D)
Chart 3 – 14 V LED Flashing AMBER/ 28V LED Off – No Alternator Output – Test OVCO Circuit
Unplug alternator-to-regulator 4-socket harness from regulator. At receptacle on regulator, connect red lead
from DMM to pin C. Connect black lead to B– terminal. Does resistance read OL (out of limits)?
Yes
TT
T
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Alternator is defective.
Chart 4 – 28 V LED Flashing AMBER/ 14V LED Off – NO Alternator Output – Test OVCO Circuit
Unplug alternator-to-regulator 4-socket harness from regulator. Connect red lead from DMM to pin A in
plug. Connect black lead to pin D in plug. Does resistance read 2.2 ± 0.2 ohms?
Yes
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With red lead from DMM connected to pin A in plug, connect black lead to B– terminal. Does
resistance read OL (out of limits)?
Ye s
TT
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Replace existing regulator with known good regulator.
Run engine. Does OVCO trip?
Ye s
No
Replace regulator with known good regulator.
Run engine. Does OVCO trip?
Yes
TT
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Alternator
is defective.
No
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Alternator is defective.
No
TT
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No
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Original regulator
is defective.
No
TT
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Alternator is defective.
TT
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TT
Alternator is defective.
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
Original regulator
is defective.
C. E. Niehoff & Co.• 2021 Lee Street • Evanston, IL 60202 USA
Page 8
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Figure 6 – Alternator-to-Regulator 4-Socket Harness Plug
E-mail us at support@ceniehoff.com
SOCKET
CONNECTIONS
AF–
B Phase Signal AC
CB–
D 28 V B+
TG0027A
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