Erratic Voltage Regulation; High Voltage; Rectifier Testing - Kohler 6VSG Service Manual

• Double-check connections to the output blocks.
High indicated voltage may indicate incorrect
calibration; recalibrate the voltage metering for the
controller.
• The AC output of the generator (measure across
leads 1-2, 2-3, and 3-1 before the rectifier).
If the AC output of the generator is good (>50% of
nameplate voltage) and the DC output is low, check
the rectifier to verify that it is working correctly (see
Section 5.3).
• Open the generator output breaker and measure
the DC voltage at the rectifier; this will remove the
possibility of an external short circuit or excessive
load.
• If the voltage recovers when the output breaker is
opened, it is possible that the rectifier is not
operating correctly. Follow rectifier troubleshooting
in Section 5.3.
• Stop the generator and remove the stator leads from
the rectifier. Make sure that the controller sensing
leads are still connected to the stator leads before
restarting the generator.
• Restart the generator and check the voltage
between each disconnected stator lead. If there is
voltage (>50% of nameplate) on the leads when
they are disconnected, there may be an internal
short in the rectifier.
Note: There should not be voltage between leads 1
and 4, 2 and 5, and 3 and 6 on the 24V 6VSG
unit. If there is more than 2V between each
pair, there may be an internal alternator short.
If the output voltage is low, but not below 85% of the
generator rating, check the following with the engine
running in run:
• The load on the generator (may be in current limit
mode)
• The controller calibration
• The Voltage Regulator gain (try increasing gain to
see if the voltage will increase)
• The engine speed (has the engine reached the
maximum operating speed)
• Open the output breaker and see if the generator
voltage (as displayed on the controller) recovers.
5.2.2

Erratic Voltage Regulation

If the voltage is unstable, check the following:
The output voltage of the 6VSG is determined by the
speed that the engine is running. Unstable engine
66 Section 5 Component Testing and Adjustment
speed will cause unstable voltage. Unstable loading
may drive unstable engine speed.
Engine Speed Stability – If the engine speed is stable,
try tripping the output breaker and watching the
rectifier voltage to see if it stabilizes. If the engine
speed is unstable, try changing the voltage regulator
gain and the engine speed governor gain. Increasing
the gain may help to remove a slower instability;
decreasing the gain may remove a faster-cycling
instability.
Note: Often engine speed instability is caused by
mechanical obstructions of the throttle plate,
ignition issues such as worn spark plugs, or fuel
supply inadequacies. Pressure biasing on the
pressure regulator may also affect engine
stability.
If the engine speed stabilizes with the removal of load,
check whether the load is changing quickly due to a
nonlinear load connected to the same DC bus.
If the engine speed is stable, but the voltage is varying
significantly, check for load stability and for loose
connections on the rectifier. Verify rectifier operation
(see Section 5.3).
5.2.3

High Voltage

The following guide can help to identify the cause of
abnormally high output voltage:
Check the controller calibration – if the controller reads
accurately, check the
(increase gain to see if voltage will correct).
1. Check the Voltage Regulator Average Voltage
Adjustment.
2. Check whether the engine speed is matching the
target speed (using Kohler SiteTech).
3. Check for speed stability (fuel supply, throttle
linkage, gains, etc.).

5.3 Rectifier Testing

The 6VSG supplies AC voltage from the alternator to a
3-phase, full-wave rectifier to produce a low-ripple DC
voltage to supply to the load. Figure 5-1 illustrates the
rectifier connections on the 6VSG. The 24V 6VSG
uses three individual rectifier blocks to handle the high
current output of the 24V 6VSG, while the 36V and
48V 6VSG generators use a single block 3-phase
rectifier because they produce less current.
If the rectifier is believed to be malfunctioning, follow
the following instructions to help determine if the
rectifier is working correctly.
Voltage Regulator Gain
TP-6844 1/13