Section 8 Component Testing And Adjustment; Theory Of Operation; Separate Excitation - Kohler 6EKOD Service Manual

8.1 Theory of Operation

These generator sets utilize a rotating-field alternator to
produce AC voltage. Upon activation of the generator
start button, DC current from the battery magnetizes the
rotor (field). When the magnetized rotor rotates within
the stator windings, an electrical voltage develops within
the stator. As engine speed and generator output
increase, the ADC IId feeds rectified stator output
current to the rotor through the exciter (or brushes/slip
rings for model 6EKOD/5EFKOD) to increase the
strength of the rotor field. As the rotor field increases in
strength, generator output also increases. The ADC IId
monitors the generator output voltage through leads 11
and 44 (for 1-phase models) or leads V7, V8, and V9 (for
3-phase models) and adjusts the DC current to the rotor
to meet load requirements. See Figure 8-1.

8.2 Separate Excitation

To determine the cause of no- or low-AC output, refer to
the troubleshooting flowchart in Figure 8-2. Before
beginning the test procedures, read all of the safety
precautions at the beginning of this manual. Many of the
test procedures include additional safety precautions.
Check the condition of the alternator fuse (F1) before
performing the separate excitation procedure. See
Figure 8-1. See Figure 1-2 for the fuse location. If the
fuse is not blown, use the following procedure to
separately excite the generator using an external
voltage source (a 12-volt automotive battery).
Separately exciting the generator can identify faulty
voltage regulation by the ADC IId controller or reveal a
running fault in the rotor and/or stator. An external
power source duplicates the role of the voltage regulator
and excites the generator field (rotor). A generator
component that appears to be in good condition while
stationary may exhibit a running open or short circuit
while moving. Short circuits can be caused by
centrifugal forces acting on the windings during rotation
or insulation breakdown as temperatures increase.
TP-6774 2/14a

Section 8 Component Testing and Adjustment

1
ADC IId
55F
66
FN
FP
11
4
44
44
8
7
6
1. Fuse
2. Power lead (55)
3. Excitation to rotor
4. Exciter (or brushes/slip
rings)
5. Rectifier module
6. Main field (rotor)
Figure 8-1 Generator Schematic
(Single-Phase Model Shown)
No Generator Output
Separate Excitation
Erratic or No Output
Check Rotor
Figure 8-2 General Troubleshooting
Section 8 Component Testing and Adjustment
55 2
66
3
FN
3 2 1 11
55
66
F +
AC
AC
AC
F --
5
4
7. Stator windings
8. Sensing leads
(11 and 44 for
1-phase models or
V7, V8, and V9 for
3-phase models)
Output within
Specifications
Check Wiring,
Fuses,
and ADC IId
Check Stator
TP563273
FP
73