C.E. Niehoff & Co. C709, C725 Troubleshooting Guides

C.E. Niehoff & Co.

C709 and C725 Alternators

Troubleshooting Guide

Hazard Definitions

These terms are used to bring attention to presence of hazards
of various risk levels or to important information concerning
product life.
Indicates presence of hazard(s)

CAUTION

that will or can cause minor
personal injury or property
damage if ignored.

Indicates special instructions on

NOTICE

installation, operation or mainte­ nance that are important but not
related to personal injury hazards.

Table of Contents

Section A: Wiring Diagram ......................................2

Section B: Basic Troubleshooting ............................3

Section C: Advanced Troubleshooting ................ 4 – 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.

TG64B

Page 1

Section A: Description and Operation

CEN C709 and C725 Dual Voltage Alternators
Description and Operation

C709 and C725 240 A (28 /14 V) dual voltage alterna­tors are internally rectified. All windings and current­conducting components are non-moving, so there are no
brushes or slip rings to wear out. Energize switch (com­monly an oil pressure switch or ignition switch) acti­vates regulator. Field coil is then energized when rota­tion is detected. Upper voltage (28 V) is rectified with
standard diodes. Lower voltage (14 V) circuit output cur­rent is controlled by SCRs. Alternator output current is
self-limiting and will not exceed rated capacity of alter­nator.

A2-329 regulator used with these units also

• is flat temperature compensated. Setpoints are 28.0
± 0.2 V and 14.0 ± 0.2 V.

• provides overvoltage cutout (OVCO). Regulator will
trip above 32 V for 28 V system (16 V for 14 V
system) longer than 2 seconds. OVCO feature detects
high voltage and reacts by signaling relay in F–
alternator circuit to open, turning off alternator.
Restarting engine resets OVCO circuit. If vehicle is
run in OVCO mode, OVCO will automatically reset
when system charging voltages drop below 11 V for
both 14 and 28 volt batteries. Regulator
regains control of alternator below output voltage.

• maintains alternator output voltage at regulated
settings as vehicle electrical loads are switched
on and off.

28 V B+
terminal

14 V B+
terminal

B– terminal







E terminal



Figure 1 — C725 Alternator and

A2-329 Regulator Terminals

Page 2

Figure 2 — C709 and C725 Alternators with A2-329 Regulator

TG64B

Section B: Basic Troubleshooting

Tools and Equipment for Job

• Digital Multimeter (DMM)

• Ammeter (digital, inductive)

• Jumper wires

Identification Record

List the following for proper troubleshooting:

Alternator model number _________________________



Regulator model number ________________________



Setpoint listed on regulator _______________________



Preliminary Check-out

Check symptoms in Table 1 and correct if necessary.

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 alternator or

regulator.

Check: wrong regulator.

Check: defective regulator.

Check: alternator.

Check: presence of energize signal.

Check: battery voltage at alternator

output terminal.

Check: defective alternator or

regulator.

Go to Chart 2, page 6.

ACTION

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.
Nominal battery voltage for 28 V systems is 25.2
±0.2 V; for 14 V systems is 12.6 ±0.2 V. Less than
25 V or 12.4 V indicates no charge condition when
engine is running.

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 at batteries with engine
running (nom. 27-28 V or 13.5-14.0 V).

If charge voltage is above 32 V

for 28 V system 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 Table 1
at left.

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
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.

8. If charging system is not performing properly,
go to Chart 1, page 5.

CAUTION

TG64B

Page 3

Section C: Advanced Troubleshooting

A2-329 Regulator

DESCRIPTION AND OPERATION

A2-329 Regulator with OVCO is attached directly to the
outside of alternator. Regulator setpoint has f lat temper­ature compensation. Voltage setpoint is 28.0 ±1.0 V and

14.0 ±0.5.

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 3 seconds of reading
voltage above 16 V. OVCO feature detects overvoltage
and reacts by disabling the alternator field circuit.
This turns off alternator. OVCO circuit will reset by
either:
— Restarting engine (regulator regains control of
alternator output voltage) OR

— System voltage on both 14 and 28 volt batteries

falling below 11 V. OVCO will automatically reset.

• 28 V side trips at voltage higher than regulator

setpoint that exists longer than 3 seconds of reading
voltage above 32 V. OVCO feature detects overvoltage
and reacts by disabling the alternator field circuit.
This turns off alternator. OVCO circuit will reset by
either:
— Restarting engine (regulator regains control of
alternator output voltage) OR

— System voltage on both 14 and 28 volt batteries

falling below 11 V.

Trou ble sh oot ing

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, includ­ing loose battery cables, both positive and negative. If
battery disconnects from system, it could cause overvolt­age 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, 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 3a or 3b, page 7.

Page 4

TG64B

Section C: Advanced Troubleshooting (CONT’D)

Chart 1 – No 28V Alternator Output – Test Charging Circuit

STATIC TEST – KEY ON, ENGINE OFF

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

Yes



Regulator responded to overvoltage condition.
Go to Chart 3 on page 7 to troubleshoot OVCO.

Shut off engine. With key on, engine off: Test for battery voltage at alternator 28 V B+
terminal. Does battery voltage exist?

Yes



Jumper 28 V B+ terminal on alternator to E terminal on regulator. Run engine.
Wait 10 seconds. Does alternator charge?

Yes



No energize signal is present. Repair wiring harness
in vehicle energize circuit. Retest alternator.

No



No



Repair vehicle wiring or recharge/replace batteries
as necessary. Continue test.



No



CAUTION

When performing the
following test, connect
jumper wire away from
pin A or not at pin A.
Spark may erode pin.

Turn off engine, leave key off. Remove alterna­tor-to-regulator 5-pin harness from regulator.
Momentarily (1 second) connect jumper wire
from pin 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?

Yes



Regulator is
defective.

PIN CONNECTIONS
A F–
B unused
C B–
D 28 V B+
E Phase

Figure 3 – Alternator-to-Regulator 5-Pin Harness Plug

No



Alternator is
defective.

TG64B

Page 5

Section C: Advanced Troubleshooting (CONT’D)

Chart 2 – No 14 V Alternator Output – Test Circuit

Before starting test:

1. Remove 14 V B+ cable at alternator. Insulate cable to prevent arcing.

2. Connect test light across 14V B+ terminal on alternator and B–terminal on alternator.

Connect jumper from pin C on alternator-to-regulator 3-socket harness plug to 28 V B+ terminal
on alternator. Does test light glow brightly?

Yes

Alternator is defective.



Substitute a known good regulator. Run engine. Is regulator setpoint
voltage present?

Yes

No

No



Original regulator
was defective.

Alternator is
defective.

SOCKET CONNECTIONS

A 14 V B+

A

C

B unused

B

C 14 V Control



Page 6

Figure 4 – Alternator-to-Regulator 3-Socket Harness Plug

TG64B

Section C: Advanced Troubleshooting (CONT’D)

Chart 3 – OVCO Trip – Determine 28 V or 14 V

With meter red lead on 28 V B+ at battery and black lead on chassis ground, start engine.

Watch meter dial: Does meter read battery charge above 29 V?

Yes



28 V side tripped OVCO circuit.
Go to Chart 3b.

Chart 3a – No 14 V Alternator Output – Test OVCO Circuit

Disconnect alternator-to-regulator 3-pin 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

14 V side tripped OVCO circuit.
Go to Chart 3a.



Alternator is defective.

PIN CONNECTIONS

C

B

Figure 5 – Alternator-to-Regulator 3-Pin Harness Receptacle

A 14 V B+

A

B unused
C 14 V Control

Chart 3b – No 28 V Alternator Output – Test OVCO Circuit

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

Yes



Alternator is defective.

No



No



No



Original regulator
is defective.

Unplug alternator-to-regulator 5-pin harness from regulator. Connect red lead from DMM to pin A in plug. Connect
black lead to pin D in plug. Does resistance read 1.0 ± 0.2 ohms?

Yes

No



Alternator is defective.



Set DMM to auto-ranging scale. Connect red lead from DMM to pin A in plug. Connect black lead
to B– terminal. Does resistance read OL (out of limits)? Then connect red lead to pin D and 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 6 – Alternator-to-Regulator 5-Pin Harness Plug

No



PIN CONNECTIONS
A F–
B unused
C B–
D 28 V B+
E Phase

TG64B

Page 7

Section C: Advanced Troubleshooting (CONT’D)

14 V Functions

Normal Resistance

Lead Connections from DMM Reading Component Tested

red to pin C in 3-pin receptacle and
black to socket C in 5-socket receptacle OL* 14 V control signal

red to socket C in 3-socket plug and SCR gate in
black to socket A in 3-socket plug 7-13 anti-drive end housing

28 V Functions

Lead Connections from DMM Normal
to 5-socket Receptacle Reading Component Tested

red to socket A and black to socket C OL* (resistance) Power transistor

Short tone on
red to socket A and black to socket D Diode Checker* Supressor diode

* If readings register other than those shown, regulator is defective.
** If readings register other than those shown, anti-drive end housing is defective.

5-PIN CONNECTIONS
A F–
B unused
C B–
D 28 V B+
E Phase

Figure 7 – Alternator-to-Regulator 5-Pin Harness Plug Figure 8 – Alternator-to-Regulator 3-Socket

5-SOCKET CONNECTIONS
A F–
B unused
C B–
D 28 V B+
E Phase

Figure 9 – Alternator-to-Regulator Harness Connections at Regulator – 5-Socket Receptacle and 3-Pin Receptacle

A

B

E

C

D

C

A

C

B

A

B

A 14 V B+
B unused
C 14 V Control

3-SOCKET CONNECTIONS
A 14 V B+
B unused
C 14 V Control

Harness Plug

3-PIN CONNECTIONS

If you have quest ions about your alternator or any of these test procedures, or if you need to locate a Factory Authorized Service Dealer, please contact us at:

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

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

E-mail us at [e-mail]

Page 8

TG64B