700 Series Troubleshooting Guide
for C720 Alternator
Hazard Definitions
These terms are used to bring attention to presence of hazards
of various risk levels or to important information concerning
product life.
CAUTION
NOTICE
Indicates presence of hazards that
will or can cause minor personal
injury or property damage.
Indicates special instructions on
installation, operation or maintenance 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
Battery Conditions
NOTICE
conditions may be observed during cold start voltage tests.
• Maintenance/Low Maintenance Battery:
— Immediately after engine starts, system volts are
lower than regulator setpoint, and amps are
medium.
— 3-5 minutes into charge cycle, system volts
increase and 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 characteris-
tics with slightly longer recharge times.
• Maintenance-free Battery:
— Immediately after engine starts, system volts are
lower than regulator setpoint with low charging
amps.
— Once the charge cycle begins, low volts and low
amps are still present.
— After the alternator energizes, volts will increase
several tenths. Amps will increase gradually,
then quickly to medium to high amps.
— Finally, volts increase to setpoint and amps
will 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.
Until temperatures of electrical
system components stabilize, these
Charge Volt and Amp Values
Voltage and amperage levels are functions of the battery
state of charge. If batteries are in a state of discharge,
as after extended cranking time to start the engine,
system volts when measured after the engine is started
will be lower than the regulator setpoint, and system
amps will be high. This condition is normal for the
charging system. 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.
Voltage and amperage readings will change: System
voltage reading will increase to regulator setpoint, and
system amps will decrease to low level (depending on
other loads) as batteries recover and become fully
charged.
• 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 amp value that can cause
battery temperature to rise above adequate charging
temperature within 4-8 hours of charge time. To
prevent battery damage, charge amps should be
decreased when battery temperature rises. Check
battery manufacturer recommendations on proper
rates of charge amps.
• High Amps: System amp value that can cause
battery temperature to rise above adequate charging
temperature within 2-3 hours. To prevent battery
damage, charge amps should be decreased when the
battery temperature rises. Check battery manufacturer recommendations on proper rates of charge
amps.
• Battery Voltage: Steady-state volt value measured
with battery in open circuit with no battery load.
This value relates to battery state of charge.
• Charge Voltage: Volt value obtained when charging
system is operating. This value will be higher than
battery voltage and must never exceed the regulator
voltage setpoint.
• B+ Voltage: Volt value obtained when measuring
voltage at battery positive terminal or alternator B+
terminal.
• Surface Charge: Higher-than-normal battery voltage
occurring when battery is removed from battery
charger. Surface charge must be removed to determine true battery voltage and state of charge.
• Significant Magnetism: Change in 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: Normal condition which
occurs when the load demand on an alternator is
greater than rated alternator output at given rotor
shaft RPM.
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Page 1
Section A: Wiring Diagrams
CEN C720 Alternator
Description and Operation
C720 28 V (300 A) alternator is self-rectifying.
All windings and current-transmitting components
are non-moving, so there are no brushes or slip rings
to wear out. The alternator has a DF (orD+) terminal
for a charge warning lamp, and a W terminal for a
tachometer or control circuit.
When controlled by the A2-206 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.
Regulator has overvoltage cutout (OVCO). Regulators
with OVCO (overvoltage cutout) will trip at vehicle
electrical system voltages above 33 volts that exist
longer than 3 seconds. OVCO feature detects high
voltage and reacts by signaling F+ alternator circuit
to open. This turns off alternator. Restarting engine
resets OVCO circuit. Regulator regains control of
alternator output voltage.
B+ terminal stud
W terminal
DF (D+)
terminal
Figure 1 — C720 Alternator Terminals
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B– terminal
stud
Page 2
Figure 2 — C720 Alternator with A2-206 Regulator
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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 _____________________
❏
Setpoints 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
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: broken drive belt.
Check: battery voltage at alter-
nator output terminal.
Check: defective alternator
and/or regulator.
Check: lost residual magnetism
in self-energizing alternator.
Go to Chart 1, page 4.
ACTION
Basic Troubleshooting
1. Inspect charging system components for
damage
Check connections at B– cable, B+ 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 voltages and states 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.
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.
CAUTION
shut down system. Electrical system damage may occur if
charging system is allowed to operate at high 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
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.
If charge voltage is above
33 volts, immediately
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Page 3
Section C: Advanced Troubleshooting
Chart 1 – No Output
Self-energized alternator may have lost magnetism. Touch steel tool
to shaft to detect any magnetism. Is shaft magnetized?
Ye s
Momentarily (1 sec.) jumper DF (D+) terminal on alternator to
B+ terminal on alternator. Touch shaft with steel tool to detect
any magnetism. Is shaft magnetized?
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Operate alternator. Does voltage output exist?
Yes
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System operating normally.
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Unplug alternator-to-regulator harness. Plug CEN Regulator Bypass Adapter A10-129 into harness plug. Clip
red lead to B+ terminal on alternator. Touch black lead to ground on alternator case. (If Adapter is not available, connect jumper wires from pin B on harness to alternator B+ terminal and from pin C on harness to
ground.) Spark will occur at ground. Touch steel tool to shaft to detect any magnetism. Is shaft magnetized?
Ye s
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Disconnect Adapter or jumper wires.
No
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No
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No
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Alternator is defective.
No
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Check for battery voltage across pins A and E on plug end of harness. Does voltage exist?
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Disconnect battery cable to B+ terminal on alternator. Connect
red lead of DMM to pin B on plug end of harness. Connect black
lead to pin C on plug end of harness. Does continuity exist?
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Alternator is defective.
Connect red lead of DMM to ground on alternator case.
Connect black lead to pin D on plug end of harness.
Does continuity exist?
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Regulator 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:
C. E. Niehoff & Co.• 2021 Lee Street • Evanston, IL 60202 USA
TEL: 800.643.4633 USA and Canada • TEL: 847.866.6030 outside USA and Canada • FAX: 847.492.1242
Page 4
Alternator is defective.
E-mail us at support@ceniehoff.com
No
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No
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Alternator is defective.
No
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PIN CONNECTIONS
Alternator-to-Regulator Harness Plug
Pin A B–
Pin B Field +
Pin C Field –
Pin D AC
Pin E B+
Figure 3 –
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