C.E. Niehoff & Co. C726 Troubleshooting Guides

C726 Alternator

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 hazards that

CAUTION

will or can cause minor personal
injury or property damage.

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 – 5

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+ Volta ge: 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 intensi-
ty 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.

TG69A

Page 1

Section A: Wiring Diagram

CEN C726 Alternator
Description and Operation

C726 42 V 380 A alternator is 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, A2-339 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.

A2-339 regulator used with these units also

• is negative temperature compensated. Setpoint is

42.0 V at 72 F.

• provides overvoltage cutout (OVCO). Regulator
will trip OVCO when system voltage rises above
46 volts for longer than 3 seconds. OVCO feature
detects high voltage and reacts by opening alter­nator field circuit and turning off alternator.
Removing and reapplying energize signal at IGN
terminal will reset OVCO circuit.

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

B–
terminal

IGN terminal

B+ terminal





Figure 1 — C726 Alternator and

A2-339 Regulator Terminals



P terminal



Page 2

BR

R

R

BK

G

BR

W

G

Figure 2 — Wiring Diagram

H
G

F

E

D

C
B

A

TG69A

Section B: Basic Troubleshooting

Tools and Equipment for Job

• Digital Multimeter (DMM)

• Ammeter (digital, inductive)

• Jumper wire

Identification Record

List the following for proper troubleshooting:



Alternator model number ______________________



Regulator model number _____________________



Setpoints listed on regulator ___________________

Preliminary Check-out

Check symptoms in Table 1 and correct as necessary.

TABLE 1 – 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 IGN terminal
on regulator.

Check: battery voltage at alter-

nator output terminal.

Check: defective alternator

and/or regulator.

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 batter­ ies 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.
If charge voltage is above

46 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.

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 4.

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 4.

CAUTION

TG69A

Page 3

Section C: Advanced Troubleshooting

Chart 1 – No Alternator Output – Quick Diagnostic

With engine running: Does battery voltage exist at alternator B+ terminal and regulator IGN terminal?

Yes

Repair vehicle harness circuit to IGN terminal on regula-



With key off, engine off: Does battery voltage exist at alternator B+ terminal?

Yes



CAUTION

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?

With DMM on resistance scale, does the field resistance between pins F and A in harness plug measure about

3.2 (±0.2) ohms?

Set DMM to diode test. Check continuity of 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. 0.3 to 0.6 V).
Disconnect leads. Connect red lead to alternator B– terminal. Connect black lead to pin B.
Meter should read one diode drop (approx. 0.3 to 0.6 V).

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. 0.3 to 0.6 V).
Disconnect leads. Connect red lead to alternator B– terminal. Connect black lead to pin H. Meter should read
one diode drop (approx. 0.3 to 0.6 V).

Go to Page 5 to continue.

When conducting this step, ensure that the probes do not touch other pins, as an arc may damage the
wiring in the harness.

Yes



Yes



Yes No



Yes



tor 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



No



No



No





No



Page 4

CONNECTIONS

A F–



B AC 1



C B–



D B+/Kelvin−



E Temp



F F+/D+



G Kelvin+



H AC 2



Figure 3 – Alternator-to-Regulator Harness Plug

A

B

G

F

E

C

H

D

TG69A

Section C: Advanced Troubleshooting (CONT’D)

Chart 1 cont’d from Page 4 – No Alternator Output – Quick Diagnostic

With DMM on resistance scale: Connect red lead to pin D in harness plug. Connect black lead to alternator
B+ terminal. Meter should read 0 ohms. Change pin D to pin G. Meter should read 0 ohms.

Yes

Alternator is defective.



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? Repeat magnetism test for pin A.

Yes



Regulator is defective.

Alternator is defective.

No



No



CONNECTIONS

A F–



B AC 1



C B–



D B+/Kelvin−



E Temp



F F+/D+



G Kelvin+



H AC 2



Figure 4 – Alternator-to-Regulator Harness Plug

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

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

TG69A

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

E-mail us at [e-mail]

A

B

G

F

E

C

H

D

Page 5