Atlas Copco QAS28 Yd(S) - Alternator and Engine Troubleshooting; Alternator Fault Diagnosis; Engine Starting Problems

INSTRUCTION MANUAL
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The table below gives an overview of the possible engine problems
and their possible causes.
The starter motor turns the engine too slowly
– Battery capacity too low.
– Bad electrical connection.
– Fault in starter motor.
– Wrong grade of lubricating oil.
The engine does not start or is difficult to start
– Starter motor turns engine too slowly.
– Fuel tank empty.
– Fault in fuel control solenoid.
– Restriction in a fuel pipe.
– Fault in fuel lift pump.
– Dirty fuel filter element.
– Air in fuel system.
– Fault in atomisers.
– Cold start system used incorrectly.
– Fault in cold start system.
– Restriction in fuel tank vent.
– Wrong type or grade of fuel used.
– Restriction in exhaust pipe.
Symptom Possible cause Corrective action
Alternator does not excite. Blown fuse. Replace fuse.
Insufficient residual voltage. Increase the speed by 15 %.
No residual voltage. For an instant apply on the + and – terminals of
the electronic regulator a 12 V battery voltage
with a 30
Ω resistor in series respecting the polar-
ities.
After being excited alternator
does not excite.
Connections are interrupted. Check connection cables as per attached draw-
ings.
Low voltage at no load. Voltage potentiometer out of setting. Reset voltage.
Intervention of protection. Check rpm.
Winding failure. Check windings.
High voltage at no load.
Voltage potentiometer out of setting. Reset voltage.
Failed regulator. Substitute regulator.
Lower than rated voltage at
load.
Voltage potentiometer out of setting. Reset voltage potentiometer.
Intervention by protection. Current too high, power factor lower than 0.8;
speed lower than 4 % of rated speed.
Failed regulator. Substitute regulator.
Rotating bridge failure. Check diodes, disconnect cables.
Higher than rated voltage at
load.
Voltage potentiometer out of setting. Reset voltage potentiometer.
Failed regulator. Substitute regulator.
Unstable voltage.
Speed variation in engine. Check regularity of rotation.
Regulator out of setting. Regulate stability of regulator by acting on
“STABILITY” potentiometer.