Theory Of Operation; Brushless Generator Sets; Output Voltage And Frequency; Voltage Rating And Rotation Speed - Kohler 4EOZ Service

9.2 Theory of Operation,

Brushless Generator Sets

These generator sets use a two-pole, revolving-field
alternator.
The generator set's alternator is a "brushless" design,
utilizing capacitor excitation. This system does not use
brushes, slip rings, or a voltage regulator. In order to
obtain generator output, the rotor (field) must be
energized and moving. The rotor is directly connected
to the flywheel by a tapered coupling. A ball bearing,
located in the stator frame, holds the rear portion of the
rotor. The engine moves the rotor (field) past the stator
main winding, which induces an AC voltage across the
stator leads. The rotor core holds enough residual
magnetism to produce low AC output from the stator
during start-up. As the generator speed increases, the
stator auxiliary winding connected to the capacitor
(leads C1 and C2) induces a voltage on the rotor field
winding. A diode on the rotor rectifies the voltage to
produce DC field current in the rotor. AC output is drawn
from the stator winding that supplied 12 VDC to the K3
relay (start protection) and feed the capacitor.
current in the stator main winding increases with the
load, additional current is induced in the rotor field to
supplement the current being supplied by the stator
auxiliary winding.
The generator cannot be disconnected or removed from
the engine as a single unit.

9.3 Output Voltage and Frequency.

The 3.5EFOZ model generator set supplies 230 volts at
50 Hz while the 4EOZ model supplies 120/240 volts at
60 Hz in accordance with the preselected winding
connection and engine speed.
52 Section 9 Generator Troubleshooting
9.3.1 Voltage Rating and Rotation
Speed
Always check the generator set's output voltage at the
nominal speed rotation. The alternators are preset at
the factory to supply voltage slightly higher (5--6%) than
the voltage at the nominal engine speed rotation.
The difference between the engine rotation and the
nominal one can cause slight deviation of output
voltage. Keep in mind that the output voltage varies
proportionally to the rotation speed. If requiring output
voltage correction of the generator set at a defined
rotation, vary the capacity of the excitation capacitor. By
increasing or decreasing the capacity value of the
capacitor, voltage changes.
Note: Do not operate the generator set with voltages
that deviate more than 10% of the nominal speed
rotation.
9.3.2

Bearing

The alternator's rear bearings are self-lubricating and
As
do not require maintenance for 10,000 operating hours.
Replace the rear bearings during a complete engine
overhaul.
TP-6137 5/03