Project Overview
A construction company operating heavy equipment relied on a diesel generator for continuous site power. They contacted PowerProKe Ltd after experiencing a complete loss of power output. The engine was running normally, but the alternator produced zero voltage, putting site operations at risk of severe delays.
This created an immediate work stoppage on site, risking project timelines and potential financial losses.
Initial Symptoms
- Engine running normally at correct RPM
- Complete loss of electrical output (0 Volts)
- Breaker tripped or failing to close
- Control panel displaying voltage faults
Initial Inspection
Our field technicians arrived on-site to perform a full technical assessment of the alternator and excitation system.
Electrical Output Testing
We measured the main terminal output and confirmed zero voltage across all phases while the engine was running at synchronous speed.
Excitation System Analysis
We tested the Automatic Voltage Regulator (AVR) and the exciter stator. The AVR was receiving power, but the excitation field was not building up.
Diagnostic Process
Diagnosing a "no output" condition requires isolating the main stator, the exciter, and the rotating diode assembly.
1Internal Component Inspection
We disassembled the alternator end to inspect the internal windings. Visual inspection revealed severe heat damage and burnt insulation on the main stator windings.
2Diode Testing
We isolated and tested the rotating rectifier diodes using a multimeter. Several diodes had failed short, which prevents the exciter rotor AC output from converting to DC for the main rotor field.
3Excitation Coil Check
Insulation resistance testing (Megger test) on the excitation coil showed a breakdown in insulation, confirming a faulty excitation coil alongside the stator damage.
Root Cause Analysis
Findings
The complete loss of power was caused by a combination of burnt stator windings, a faulty excitation coil, and failed rectifier diodes.
Repair Process
Instead of recommending a costly full alternator replacement, we implemented a complete alternator restoration in our workshop.
Full Stator Rewinding
We stripped the burnt copper wire from the main stator core, cleaned and insulated the slots, and performed a full precision rewind using high-grade, temperature-resistant copper wire and Class H insulation varnish.
Excitation Coil Rewinding
The damaged exciter stator was similarly rewound and varnished to restore the magnetic field generation capability.
Replacement of Rectifier Diodes
The entire rotating diode assembly was replaced with new, correctly rated forward and reverse diodes, and surge suppressors (varistors) were installed to protect against future voltage spikes.
Final Testing & Validation
After the repair and reassembly, the alternator was coupled back to the engine for electrical testing and calibration.
Output Restored
Generator output was fully restored to the correct 415V phase-to-phase voltage.
Stable Voltage
The AVR was calibrated to maintain stable voltage under varying load steps.
Full Operation
Equipment was brought back to full operation, handling the heavy construction loads without voltage dips.
Lessons from the Case
Key Insight: Misdiagnosis
Many generator failures are misdiagnosed as "dead generators" requiring full replacement, when the real issue is isolated to the alternator end.
Repair vs. Replace
With proper diagnosis, most of these cases are repairable through rewinding and component replacement at a fraction of the cost of a new alternator.
Preventing Similar Problems
The business impact for the client was substantial:
Minimized Downtime
Avoided costly generator downtime by completing the rewind faster than sourcing a new imported alternator.
Cost Savings
Saved significantly compared to the capital expenditure required for a complete alternator replacement.
Immediate Resumption
Resumed construction operations immediately, protecting project timelines.
Case Study FAQ
Why is my generator running but not producing power?
This usually indicates an alternator failure. Common causes include a blown AVR (Automatic Voltage Regulator), failed rectifier diodes, loss of residual magnetism, or burnt stator/rotor windings.
Can a burnt alternator be repaired?
Yes. In most cases, a burnt alternator can be fully restored through a process called rewinding, where the damaged copper coils are replaced with new wire and re-insulated.
What causes an alternator to burn out?
Alternators typically burn out due to severe overloading, unbalanced phase loading, poor ventilation causing overheating, or short circuits in the connected electrical system.
Eng. Okumu
Lead Technical Reviewer & Auditor
Specialization
Alternator Rewinding & Precision Servicing
Experience
18+ Years Industrial Power Systems
All information in this guide has been field-verified by our engineering team to meet current Kenyan Energy Regulatory Authority (EPRA) standards and manufacturer-specific diagnostic protocols for Perkins, Cummins, and Caterpillar systems.