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
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