Generator shuts down; controller shows AL12 – Generator Overvoltage

Safety first: Isolate the generator from the load (open output breaker) and ensure the set is stopped. High voltage can damage connected equipment.

• Inspect AVR connections: Open the alternator terminal box and locate the AVR (often a Stamford or Leroy-Somer type in FG Wilson sets). Check all sense and excitation wires for tightness and signs of overheating.
• Check sensing configuration: Verify that the AVR is wired for the correct phase and voltage sensing (e.g., line-to-line for 400 V 3-phase). Refer to the alternator wiring diagram.
• Measure output voltage: Start the generator in MANUAL with no load and measure line voltage with a true RMS meter. If it is significantly above nominal, stop the set.
• Adjust or replace AVR: If the AVR has a voltage adjustment pot, reduce the setting slightly and retest. If voltage remains uncontrolled, replace the AVR with the correct FG Wilson-specified part.
• Reconnect load: Once voltage is stable at nominal, close the output breaker and monitor voltage under load.