C.E. Niehoff & Co. N1245, N1248-3 Troubleshooting Guides

C.E. Niehoff & Co.

N1245 and N1248-3

Alternator Troubleshooting Guide

Hazard Defi nitions

These terms are used to bring attention to presence of hazard(s)
of various risk levels or to important information concerning
product life.
Indicates presence of hazard(s) that
will or can cause minor personal

CAUTION

injury or property damage.

Indicates special instructions on
installation, operation or mainte-

NOTICE

nance that are important but not
related to personal injury hazards.

Table of Contents

Section A: Wiring Diagrams ............................... 2 – 3

Section B: Basic Troubleshooting ............................4

Section C: Advanced Troubleshooting ................ 5 – 8

Battery Conditions

Until temperatures of electrical

NOTICE

system components stabilize, these
conditions may be observed during
cold-start voltage tests.

• Maintenance/ Low Maintenance Battery

— Immediately after engine starts, system volts are
lower than regulator setpoint, amps are medium.
— 3–5 minutes into charge cycle, system volts
increase, amps decrease.
— 5–10 minutes into charge cycle, system volts
increase to, or near, regulator setpoint and amps
decrease to a minimum.
— Low maintenance battery has same characteristics
with slightly longer recharge times.

• Maintenance-free Battery

— Immediately after engine starts, system volts are
lower than regulator setpoint, low charging amps.
— Once charge cycle begins, low volts and low amps
are still present.
— After alternator energizes, voltage will increase
several tenths. Amps will increase gradually, then
quickly, to medium to high amps.
— F i n a l l y , v o l t s w i l l i n c r e a s e t o s e t p o i n t a n d a m p s w i l l
decrease.
The time it takes to reach optimum voltage and amper­age will vary with engine speed, load, and ambient
temperature.

• 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.

• AGM (Absorbed Glass Mat) Maintenance-free Battery

These dry-cell batteries respond better than standard
maintenance-free. If battery state of charge drops to
75% or less, batteries should be recharged to 95% or
higher separately from the engine’s charging system to
avoid damaging charging system components and to
provide best overall performance. Charge acceptance of
these batteries may display
maintenance batteries.

characteristics similar to

Battery Charge Volt and Amp Values

Volt and amp levels fluctuate depending on the battery
state of charge. If batteries are in a state of discharge—as
after extended cranking time to start the engine—system
volts will measure lower than the regulator setpoint after
the engine is restarted and system amps will measure
higher. This is a normal condition for the charging system;
the greater the battery discharge level, the lower the system
volts and the higher the system amps. The volt and amp
readings will change as batteries recover and become fully
charged: system volts will increase to regulator setpoint
and system amps will decrease to low level (depending on
other loads).

• Low Amps: 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: System amps value which can cause

the battery temperature to rise above 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 charge
amp rates.

• High Amps: System amps value which can cause

the battery temperature to rise above adequate charg­ing temperature within 2-3 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 charge
amp rates.

• Battery Voltage: Steady-state voltage value as mea-

sured with battery in open circuit with no battery load.
This value relates to battery state of charge.

• Charge Voltage: 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: Voltage value obtained when measuring

voltage at battery positive terminal or alternator B+
terminal.

• Surface Charge: Higher than normal battery voltage

occurring when the battery is disconnected from
battery charger. The surface charge must be removed
to determine true battery voltage and state of charge.

• Significant Magnetism: Change in strength or inten-

sity of a magnetic field present in 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: Normal condition occurring

when the load demand on alternator is greater than
rated alternator output at given rotor shaft RPM.

© 2014, C. E. Niehoff & Co. All rights reserved.

TG44D

Page 1

Section A: Wiring Diagrams

CEN N1245 Alternator
Description and Operation

N1245 28 V (260 A) alternator is internally rectified.
All windings and current-transmitting components are
non-moving, so there are no brushes or slip rings to
wear out. Energize switch activates regulator. Field coil
is then energized.

When controlled by the N3043 regulator, this alternator
becomes self-energizing through internal diode trios.
Residual magnetic field induces small voltage in stator
and energizes field coil. Field coil continues receiving
incremental voltage until full voltage is achieved. AC is
rectified into DC output through diodes. Regulator con­trols voltage output. N3043 regulator has a D+ terminal
to provide signal to vehicle electrical system, confirming
alternator operation.

When controlled by the N3044 or N3261 regulator,
after engine is running, regulator receives energize
signal through IGN terminal. 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.These regulators are flat temperature
compensated. These regulators have:

• P terminal that can provide optional AC voltage tap.

• D+ terminal to provide optional signal to vehicle
electrical system, confirming alternator operation.

• Tricolored LED on N3261 only. See page 6.

B+ terminal



B– terminal



Figure 1 — N1245/N1248-3 Alternator Terminals

(N3043 Regulator Attached to Alternator)

P terminal



D+ terminal



D+ terminal





CEN N1248-3 Alternator
Description and Operation

N1248-3 28 V (310 A) alternator is internally rectified.
All windings and current-transmitting components are
non-moving, so there are no brushes or slip rings to
wear out. Energize switch activates regulator. Field coil
is then energized.

When controlled by the N3043 regulator, this alternator
becomes self-energizing through internal diode trios.
Residual magnetic field induces small voltage in stator
and energizes field coil. Field coil continues receiving
incremental voltage until full voltage is achieved. AC is
rectified into DC output through diodes. Regulator con­trols voltage output. N3043 regulator has a D+ terminal
to provide signal to vehicle electrical system, confirming
alternator operation.

IGN terminal

Figure 2 — N3044 Regulator Terminals

P terminal



Figure 3 — N3261 Regulator Terminals

D+ terminal





IGN terminal

Page 2

TG44D

Section A: Wiring Diagrams (CONT’D)

Figure 4 — N1245/N1248-3 Alternator with N3043 Regulator Wiring Diagram

TG44D

Figure 5 — N1245 Alternator with N3044 or N3261 Regulator Wiring Diagram

Page 3

Section B: Basic Troubleshooting

Tools and Equipment for Job

• Digital Multimeter (DMM)

• Ammeter (digital, inductive)

• Jumper wires

Identifi cation Record

List the following for proper troubleshooting:

Alternator model number ________________________



Regulator model number _______________________



Setpoint listed on regulator _____________________



Preliminary Check-out

Check symptoms in Table 3 and correct if necessary.

TABLE 1 – System Conditions

SYMPTOM ACTION

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; low regulator
setpoint.

Check: defective alternator

or regulator.

Check: wrong regulator.

Check: high regulator setpoint.

Check: defective regulator.

Check: alternator.

Check: broken drive belt.

Check: presence of energize signal

to IGN terminal on N3044
or N3261 regulator.

Check: battery voltage at alternator

output terminal.

Check: defective alternator

and/or regulator.

Check: lost residual magnetism in

alternator with N3043
regulator. Go to: Chart 2,
page 7.

Basic Troubleshooting

1. Inspect charging system components for damage

Check connections at B– cables, B+ cables,
B+ interconnect cable, B– interconnect cable, and
alternator-to-regulator harness. Repair or replace
any damaged component before troubleshooting.

2. Inspect all vehicle battery connections

Connections must be clean and tight.

3. Determine battery voltage and state of charge
If batteries are discharged, recharge or replace
batteries as necessary. Electrical system cannot
be properly tested unless batteries are charged
95% or higher. In addition, open circuit voltages
must be within ± 0.2 V.

4. Connect meters to alternator
Connect red lead of DMM to alternator anti-drive
end B+ terminal and black lead to alternator
anti-drive end B– terminal. Clamp inductive
ammeter on anti-drive end B+ cable.

5. Operate vehicle
Observe charge voltage at batteries with engine
running (nom. 27-28 V).

If charge voltage is above
32 V, immediately shut
down system. Electrical
system damage may occur if
charging system is allowed
to operate at excessive
voltage. Go to Table 2.

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 in­ crease 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.

9. If charging system is not performing properly,

• N3043—Chart 1, page 5

• N3044 or N3261—Chart 2, page 7

CAUTION

go to:

Page 4

TG44D

Section C: Advanced Troubleshooting

Chart 1 – No Alternator Output – N3043 Regulator

CAUTION

With key on, engine off: Momentarily (1 sec.) jumper D+ terminal on regulator to B+ terminal on alternator.
Touch shaft with steel tool to detect significant magnetism. Is shaft magnetized?

When performing the following test, do not allow jumper to contact B+ terminal more than a few
seconds. Internal fuse may blow. Wait 20 minutes before repeating test to allow fuse to reset.

Yes



Remove jumper from D+ to B+.

No





CAUTION

With key off, engine off: Unplug alternator-to-regulator harness.
Connect DMM across pin D and pin C in harness plug. Does battery
voltage exist?

Yes

When performing the following test, ensure that
the probes do not touch other pins, as an arc may
damage the pins and wiring in the harness.

No



Alternator is defective.



Set DMM to diode test. Connect black lead of DMM to pin B in harness
plug. Connect red lead to B-terminal or alternator. DMM should read
voltage drop. Reverse leads. DMM should read OL.

Yes

No



Alternator is defective.



CAUTION

With key on, engine off: Install a jumper from B+ terminal on alternator to pin B in harness plug. Momentarily
(1 sec.) jumper pin A to B– terminal on alternator. Touch shaft with steel tool to detect significant magnetism.
Is shaft magnetized?

When performing the following test , ensure that the jumpers do not touch other pins, as an arc may
damage the pins and wiring in the harness. Always connect jumper wires away from pins or not at pins.
Spark may erode pin.

Yes



Regulator is defective.

CONNECTIONS
A F–
B F+/D+
C B–
D B+
E Phase

Figure 6 – Alternator-to-Regulator Harness Plug

Alternator is defective.



No



TG44D

Page 5

Section C: Advanced Troubleshooting (CONT’D)

N3044 and N3261 Regulators

DESCRIPTION AND OPERATION

N3044 and N3261 regulators are mounted directly to

the outside of the alternator.

Main diagnostic feature of N3261 regulator consists of a
tricolored (green, amber, red) LED located on the top of
the regulator. The LED works like a voltmeter, measur­ing charging voltage. See Table 2 for diagnostic features
and LED explanations.

N3044 and N3261 regulators have OVCO (overvoltage
cutout) and will trip at vehicle electrical system voltage
above 32 volts that exists longer than 3 seconds. OVCO
feature detects high voltage and reacts by signaling relay
in F+ alternator circuit to open. This turns off alterna­tor (LED on N3261 is solid RED). OVCO circuit is reset
when engine is restarted. Regulator then regains control
of alternator output voltage.

TABLE 2 – N3261 Regulator Diagnostics

LED COLOR

AMBER Flashing

RED Flashing

Solid

CLEAR LED off

Alternator and regulator operating normally.GREEN Flashing

System voltage is lower than setpoint—electrical
load exceeds alternator rating at present rotor
speed.

System voltage higher than setpoint.

OVCO tripped.

Energize circuit fault.

STATUS

Trou b le sh oot in g

Shut down vehicle and restart engine. If alternator
functions normally after restart, a “no output condition”
was normal response of voltage regulator to “high volt­age” condition. Inspect condition of electrical system,
including loose battery cables, both positive and
negative. If battery disconnects from system, it could
cause “high voltage” condition in electrical system,
causing OVCO circuit to trip.

If you have reset alternator once, and electrical system
returns to normal charge voltage condition, there may
have been a one time, high voltage spike, causing OVCO
circuit to trip.

If OVCO circuit repeats cutout a second time in short
succession and shuts off alternator relay circuit, try
third restart. If OVCO circuit repeats cutout, go to Chart
3, page 8.

ACTION

No action required.

When loads decrease or speed increases, LED
should be flashing GREEN. If not, check drive
belt and charging system connections.

If flashing more than 3 seconds, OVCO will trip,
disabling charging system. LED will flash RED.

Overvoltage condition. System diagnosis
required. Go to Chart 3, page 8.

Check for system voltage at IGN terminal on regu­lator. If OK, replace regulator. If not OK, check
vehicle wiring a nd ignition circuit.

Page 6

TG44D

Section C: Advanced Troubleshooting (CONT’D)

Chart 2 – No Alternator Output – N3044 or N3261 Regulator

Shut down vehicle and restart engine. Does alternator function normally after restart?

Yes No



Regulator responded to overvoltage condition. Go
to Chart 3 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?

Yes

No



Repair vehicle battery circuit wiring as necessary. Continue test.



With key on, engine running: Test for battery voltage between IGN terminal on regulator and alternator B– termi­nal. Does 28 V battery voltage exist?

Yes No





Repair vehicle ignition circuit wiring as necessary. Continue test.



With key off, engine off: Remove alternator-to-regulator harness from regulator. Test for battery voltage across
sockets D and C in harness plug. Does 28 V battery voltage exist?

Yes No





Alternator is defective.



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 socket B in plug. Does meter show 1.5 ± 0.2 ohms?

Yes No



Install a jumper wire from socket B in alternator-to-regulator harness plug to B+ terminal on
alternator. Momentarily (1 sec.) jumper socket A to B– terminal on alternator. Spark will occur.
Touch steel tool to shaft to detect significant magnetism. Is shaft magnetized?

Yes

No



Alternator is
defective.





Test phase signal going into regulator (AC). Set meter to diode tester:

Connect red lead of DMM to socket C of alternator-to-regulator
harness plug and black lead to socket E of plug. Meter should show
voltage drop value.

Then reverse meter lead connections. Meter should show OL
(blocking).

Yes



Regulator is defective.

Alternator is defective.

No



Figure 7 – Alternator-to-Regulator

CONNECTIONS
A F–
B F+/D+
C B–
D B+
E Phase

Harness Plug

TG44D

Page 7

Section C: Advanced Troubleshooting (CONT’D)

Chart 3 – No Alternator Output – Test OVCO Circuit – N3044 or N3261 Regulator

Unplug alternator-to-regulator harness from regulator. Connect red lead from DMM to socket A in plug.
Connect black lead to socket B in plug. Does resistance read 1.5 ± 0.2 ohms?

Yes

No



Alternator is defective.



With red lead from DMM connected to socket A in plug, connect black lead to B – terminal. Does
resistance read OL (out of limits)?

Yes



Replace existing regulator with known good regulator.
Run engine. Does OVCO trip?

Yes



Alternator is defective.

Original regulator is
defective.

No



Alternator is defective.

Figure 8 – Alternator-to-Regulator Harness Plug

No



CONNECTIONS
A F–
B F+/D+
C B–
D B+
E Phase

If you have quest ions about your a lternator or any of these test procedures, or if you need to locate a Factory Authorized Serv ice Dea ler, please contact us at:

C.E. Niehoff & Co.• 2021 Lee Street • Eva nston, IL 60202 USA

TEL: [phone] USA and Canada • TEL: [phone] outside USA and Canada • FAX: [phone]

E-mail us at [e-mail]

Page 8

TG44D