AL15
Kohler-SDMO Generator Undervoltage / Underfrequency Trip

Controller shows AL15 / Alternator Undervoltage and load is dropped

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Engine underspeed due to fuel issues, Faulty AVR, Short circuit or heavy overload on output, Loose alternator excitation connections

How to Fix / Troubleshooting

Safety first: Open the generator output breaker and disconnect non-essential loads. Set controller to OFF before inspection.

  • Check engine speed: Verify frequency on the controller (50/60 Hz). If low, address engine fuel and governor issues first.
  • Inspect load: Ensure the connected load does not exceed the generator's rated kVA. Remove large motor loads and re-test.
  • Check AVR and excitation: Inspect AVR connections and excitation leads from the alternator field. Tighten any loose terminals.
  • Measure voltage: Start the generator with no load and measure voltage. If still low, the AVR or alternator field may be faulty and require replacement or repair.
  • Reset alarm: Clear AL15 and gradually reapply load while monitoring voltage.

Persistent undervoltage with correct speed suggests alternator or AVR failure; contact a generator specialist.

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Repair Difficulty

Hard 4/5

Required Part

Automatic Voltage Regulator (AVR)
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