Atlas Copco QAS 275-325, Instruction Manual

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Alternator troubleshooting
Symptom Possible cause Corrective action
Alternator gives 0 Volt Blown fuse. Replace fuse.
No residual voltage. Excite the alternator by applying a 12V battery voltage with a 30

resistor in series on the + and - terminals of the electronic regulator,
respecting the polarities.
After being excited the alternator still
gives 0 Volt. Connections are interrupted. Check connection cables, measure winding resistances and compare
with values mentioned in the alternator manual.
Low voltage at no load Voltage potentiometer out of setting. Reset voltage.
Intervention of protection. Check frequency/voltage regulator.
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 10%
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.