F11
MTU Onsite Energy
Generator Output Undervoltage
Controller displays F11 – Generator undervoltage alarm/shutdown
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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
AVR failure or loss of excitation, Broken exciter field wiring, Shorted stator winding, Incorrect voltage sensing configuration
How to Fix / Troubleshooting
Safety first: Ensure the generator is isolated from the load and cannot start automatically.
- Confirm undervoltage: Measure generator terminal voltage during a start attempt. If voltage is significantly below nominal, proceed with excitation checks.
- Inspect AVR and wiring: Check the AVR connections, including power supply, sensing, and field output leads. Tighten any loose terminals and look for burned components.
- Check exciter field circuit: Measure resistance of the exciter field winding according to MTU specifications. Open or shorted windings indicate a failed exciter.
- Verify residual magnetism: If the generator has been idle for a long time, residual magnetism may be lost. Follow MTU procedures for field flashing if applicable.
- Replace faulty components: Replace a defective AVR or exciter assembly with MTU-approved parts.
- Re-test: Clear the F11 alarm and perform a controlled start, monitoring voltage rise and stability.
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Repair Difficulty
Hard
4/5
Required Part
Automatic Voltage Regulator (AVR)
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