Section 5 Component Testing And Adjustment; Theory Of Operation; Separate Excitation - Kohler 14RES Manual

5.1 Theory of Operation

The generator set utilizes a rotating-field alternator to
produce AC voltage. See Figure 5-1. After the engine
starts and reaches a predetermined speed (RPM), DC
current from the battery magnetizes the rotor (field).
When the magnetized rotor rotates inside the stator
windings, an electrical voltage develops in the stator.
The controller feeds rectified stator current to the rotor
through the brushes and slip rings to change the
strength of the rotor field as the load changes. As the
rotor field strength increases, the generator power
output increases (up to the rating shown on the
nameplate). The controller monitors the generator
output voltage through leads 11 and 44 and adjusts the
DC current to the rotor to meet load requirements while
maintaining the output voltage.
RDC/DC Controller
1
7
8
6
1. Circuit breaker
2. Power lead (55)
3. Excitation to rotor
4. Brushes
Figure 5-1 Single-Phase Generator Schematic
TP-6735 7/17

Section 5 Component Testing and Adjustment

2
3
4
5
TP6735
5. Slip rings
6. Main field (rotor)
7. Stator windings
8. Sensing leads (11--44)

5.2 Separate Excitation

To determine the cause of no or low AC output, refer to
the troubleshooting flowchart in Figure 5-2. Before
beginning the test procedures, read all safety
precautions at the beginning of this manual. Many of the
test procedures include additional safety precautions.
Check the condition of the alternator circuit breaker
before performing the separate excitation procedure.
The circuit breaker is located in the service access area
on the controller. See Figure 5-1. If the breaker is not
tripped, 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 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.
Centrifugal forces acting on the windings during rotation
cause a broken circuit to open, or increasing
temperatures cause the insulation to break down,
resulting in a running fault. If this test shows that the
rotor and stator are in good condition, test the voltage
regulation using the tests in Section 5.7.
No Generator Output
Separate Excitation
Erratic or No Output
Check Rotor
Figure 5-2 Generator Troubleshooting
Section 5 Component Testing and Adjustment
Output within
Specifications
Check Wiring, Fuses,
Circuit Breaker, and
Controller
Check Stator
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