Engine Speed; Inspection And Cleaning; Connections - Onan 50.0DDB-15R Series Operator's Manual And Parts Catalog

ENGINE S P E E D
Generatorfrequency is in direct ratio to enginespeed,
which is controlled by the Governor.
A Roosa-Master governor is standard equipment on
the DDB generator set. High speed and low speed
limit stops are set at the ONAN testing facility and
normally do not require further adjustment, therefore
if your set is used on continuous standby service, the
governor may never need to be touched. If however
the unit is used frequently, adjustment may be
required due to wear of internal components. This
adjustment is achieved by backing off the high speed
stop screw. Screw in the low speed adjusting screw
until the generator output frequency meter reads 60
Hz (generator on load). Turn in the high speed
adjusting screw until it bottoms; secure the locknuts.
AC GENERATOR
There are no brushes, brush springs or collector rings
on these generators, therefore they require very little
servicing. Periodic inspections, to coincide with
engine oil changes, will ensure good performance.
Generator Bearing: Inspect the bearing every 1000
hours with the unit running.
If using the unit for "prime power", replace the
bearing every 10,000 hours or two years. If using the
set for "standby", replace the bearing every five years.
Check generator voltage. It may be necessary to
make a slight readjustment of the voltage rheostat to
obtain the preferred voltage at average load.
I D L E ADJUSTING
SCREW
HIGH SPEED
ADJUSTING SCREW
B 2 4 8 - I
INJECTION PUMP
SENSITIVITY
(DROOP)
ADJUSTMENT
FIGURE 20. ROOSA-MASTER GOVERNOR
INSPECTION AND CLEANING
When inspecting the rotating rectifier assembly,
make sure diodes are free of dust, dirt and grease.
Excessive foreign matter on these diodes and heat
sinks will cause the diodes to overheat and will result
in their failure. Blow out the assembly periodically,
with filtered, low pressure air. Also check to see that
diodes and leadwires are properly torqued. The
diodes should be torqued to 30 in. Ib. or finger tight
plus a quarter turn. Blow dust out of control panel.
BATTERIES
Check the condition of the starting batteries at least
every two weeks. See that connections are clean and
tight. A light coating of non-conductive grease will
retard corrosion at terminals. Keep electrolyte at the
proper level above the plates by adding distilled
water. Check specific gravity, recharge if below 1.280.
Governor sensitivity is adjusted by rotating an exter-
nal knurled knob at the rear of the injector pump
housing. Turning inward (clockwise) shortens gover-
nor control spring making it less sensitive, thereby
increasing speed droop. Turning outward (coun-
terclockwise) has opposite effect. Adjustment can be
made with engine running. The speed droop is set at
the ONAN plant to give a regulation of 3 percent to 5
percent from no-load to full-load.
When using the generatorfrequency meter to deter-
mine engine speed, multiply frequency by 30 to
calculate engine speed.
Example: 30 x 61 (Hz) = 1830 rpm.
Adjust engine speed to 1800 r p m f o r 6 0 Hertz sets and
1500 rpm for 50 Hertz sets.
CONNECTIONS (Fuel, Exhaust, etc.)
Operator should periodically make a complete visual
inspection of the set while running at rated load.
Some of the things to check for are as follows:
1. Check all fuel and oil lines for possible leakage.
2. Inspect exhaust lines and mufflers for possible
leakage and cracks.
3. Periodically or daily, drain moisturefrom conden-
sation traps.
4. Inspect water lines and connections for leaks and
security.
5. Inspect electrical wires and connections for
security and fray damage.
If generator requires major repair orservicing, contact an authoriz-
ed Onan dealer or distributor.
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