Hobart 6921 Series Operation And Maintenance Manual Download

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(3)

Governor Control Unit Adjustment

Before making an adjustment to the control unit

(Fig. 7),

make certain that linkage between

actuator and fuel control lever

(Fig. 6)

is free and properly adjusted. There must be no lost

motion or “play” in the linkage. Be sure magnetic pickup is producing a strong, normal output.

There are three adjustment controls on the unit

(see Fig. 7)

. They are identified as:

RATED SPEED - Adjusts engine speed and generator frequency.

GAIN, and STABILITY - Adjust engine response time and stability.

To adjust control unit, proceed as follows:

a. If the control box is being adjusted for the first time, set adjustment controls as follows:

RATED SPEED control - set the rated speed control screw 6 to 8 turns counterclockwise.
This causes the engine to run below 2000 RPM when started.

NOTE: A very small screwdriver is required for this adjustment.

GAIN control - Adjust the gain control to its approximate midrange position.

STABILITY control - Adjust stability control to its full counterclockwise position.

b. Start engine and allow it to warm.

c. Place engine-generator control switch (18, Fig. 2) in

GEN

position to make electric governor

functional.

d. Turn

RATED SPEED

adjusting screw (1, Fig. 7) clockwise to increase engine speed to 2000

RPM. At 2000 RPM the frequency meter (1, Fig. 2) will indicate 400-Hz.

e. Turn the GAIN control screw (3, Fig. 7) clockwise until the engine becomes unstable. Then

turn this control counterclockwise until the engine becomes just barely stable.

f. Turn the STABILITY control screw (2, Fig. 7) slightly clockwise.

g. Repeat step (e) above, then repeat step (f).

h. Continue this procedure until the engine is no longer stable. At this point, it is necessary to

set both the gain and stability controls back to the last position at which the engine was
stable. At this position, check to see if engine stability is set properly. Do this by momentarily
shorting

terminals 3 and 4

on the control box. The engine will start to go to idle and then

return to operating speed, either stable or unstable. If the engine is still unstable, it may be
necessary to turn either the gain control or the stability control slightly counterclockwise until
the engine is stable.

The electric governor is now set. If the engine becomes unstable when load is applied, it may
be necessary to turn either the gain control or the stability control slightly more
counterclockwise until the engine again becomes stable.

NOTE: The best setting of speed, gain, and stability controls is the setting at which the frequency settles at

400-Hz as fast as possible when a load is applied, and remains stable when the load is removed.

(4)

Magnetic pickup signal

Connect a high impedance voltmeter to magnetic pickup input terminals

(5 and 6, Fig. 8

) on

control box terminal board. The voltage value at governed speed, no load, should be 4-V AC
MINIMUM.

NOTE: A signal as low as 1-V is sufficient to operate the control unit satisfactorily. No voltage indicates the

pickup is too far from flywheel teeth, or it is defective. For additional information, refer to Woodward
Governor Catalog No. 82493C in Chapter 6 of this manual.

OM-2040 / Operation and Maintenance Manual

90D20 / Generator Sets

February 28/94 Revised

Chapter 2-3

Page 13