C.E. Niehoff & Co. N1388-1 Troubleshooting Guides

1300 Series Troubleshooting Guide

for N1388-1 Alternator

Hazard Defi nitions

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

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, 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.

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.

TG0047A

Page 1

Section A: Wiring Diagrams

CEN N1388-1 Alternator
Description and Operation

N1388-1 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. Load-dump protection limits peak voltage
to less than 55 volts during maximum load change
over speed range in batteryless operation. Peak ampli­tude of voltage including ripple during normal battery­less operation is less than 40 volts. Radio noise sup­pression is in accordance with Mil-Std 461A, Notice 4
RE05 and CE07.

Ignition switch energizes regulator, and then field coil
is energized. Voltage adjustment is available on alter­nator control unit.

N3012 regulator furnished with this unit is flat tem­perature compensated at 28.1±0.15 V at 72 F.

Voltage
adjust plug
receptacle

Figure 1 — N1388-1 Control Assembly

T

Energize
receptacle

T

Regulator
receptacle

T

B+ terminal

Diagnostic
receptacle

T

T

T

T

B– terminal

Figure 2 — N1388-1 Alternator Terminals

(N3012 Regulator Attached to Alternator)

Page 2

Figure 3 — N1388-1 Alternator with N3012 Regulator

TG0047A

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 ______________________

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Regulator model number ______________________

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Setpoints listed on regulator ___________________

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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 bat-

tery 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 alterna-

tor output terminal.
Check: defective alternator

and/or regulator.

ACTION

Basic Troubleshooting

1. Inspect charging system components for

damage

Check connections at B– cable, B+ cable,
regulator-to-alternator harness, and vehicle
harnesses. 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+ ter­ minal and black lead to alternator B– terminal.
Clamp inductive ammeter on B+ cable.

5. Operate vehicle

Observe charge voltage.

If charge voltage is above

33 volts, immediately
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 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.

CAUTION

TG0047A

8. If charging system is not performing properly,
go to Chart 1, page 4.

Page 3

Section C: Advanced Troubleshooting

Chart 1 – No Output

Energize switch on, engine off: Disconnect harness from energize receptacle. Check for battery voltage
between B– terminal on alternator and socket B on energize harness plug end.

Yes

T

CAUTION

When performing the following test, be sure to connect
jumper on the ground side and not at socket A in
regulator receptacle. Connecting at ground side will pre­vent a spark from damaging the socket in the receptacle.

Ignition switch off: Reconnect energize harness. Disconnect regulator­to-alternator harness. Momentarily (1 sec.) jumper socket A in regula­tor receptacle to B– terminal on alternator. Touch shaft with steel tool
to detect any magnetism. Is shaft magnetized?

Yes

T

Check energize switch
and vehicle wiring.

With regulator-to-alternator harness and energize harness disconnected,
perform series of tests with DMM:

No

T

1) With meter set on ohms, connect red lead to pin B of energize recep­tacle and black lead to socket B of regulator receptacle. Meter should
read 40-55 ohms.

2) With meter set on ohms, check field coil resistance across socket A of
regulator receptacle and B+ terminal on alternator. Resistance should
measure less than 3 ohms.

3) With meter set on ohms, check for continuity between socket C of
regulator receptacle and B– terminal on alternator.

Did all three tests provide correct readings?

No

T

Repair vehicle wiring to
energize receptacle.

Yes

T

Regulator is defective.

ENERGIZE PIN CONNECTIONS

Pin A Not used
Pin B Energize
Pin C Not used

ENERGIZE HARNESS

PLUG END

Figure 4 — N1388-1 Control Assembly

If you have questions 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]

Energize
receptacle

T

Regulator
receptacle

T

REGULATOR SOCKET CONNECTIONS
Socket A F –
Socket B Energize
Socket C Ground
Socket D B+
Socket E Not used

Alternator is defective.

No

T

Page 4

TG0047A