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Alternator repairs

Leroy-Somer Generator Alternator Repairs & Servicing

Leroy-Somer is the alternator on many diesel generator sets. ProService Generator Repairs inspects that end when there is no voltage, low voltage, unstable voltage, or a winding fault. The diesel engine, if there is one, is a separate diagnosis.

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Technician rewinding copper windings in a generator stator

What a Leroy-Somer visit covers

Inspection starts with the complaint. No output voltage, low voltage and unstable voltage are not the same fault. Excitation, the AVR, the breaker and the wiring are checked before the windings are condemned. The wider alternator visit is on generator alternator repairs. A set that runs and the building stays dark is also covered on generator not producing power.

Winding faults and insulation deterioration are assessed when the electrical tests point there. Bearing noise and mechanical symptoms are noted when they are present. A rewind is recommended only when that is the repair, and it is linked to generator rewinding.

AVR-related problems — no output, low voltage, high voltage, unstable voltage — also sit on AVR repairs. Low voltage has its own page at generator low voltage, and voltage that will not settle is on unstable voltage. A diesel set that will not start at all belongs on diesel generator repairs, because that is an engine and control visit.

ProService Generator Repairs is not a Leroy-Somer dealer or a warranty centre. Parts follow the diagnosis and what is available for that alternator.

Symptoms

How a Leroy-Somer output fault presents

The complaint decides the first test. These are different faults even though they all look like a generator that is not doing its job.

  • Engine runs, no output at all

    The set starts and holds speed, and nothing reaches the board. The breaker, the excitation circuit, the AVR and the main windings are all candidates. A healthy engine proves nothing about the alternator end.

  • Voltage present but low

    Output appears and sits below where it should. That can be the AVR, the excitation supply, engine speed or a winding problem. It is measured on a running set rather than inferred.

  • Voltage will not settle

    Readings wander or lights flicker. A changing load, engine speed that is not held and a regulator that is not controlling properly all look similar until the engine side is settled first.

  • Output collapses under load

    Voltage looks acceptable off load and falls away when the load is applied. This separates an excitation or winding limitation from a simple regulator setting.

  • Voltage high or rising

    Over-voltage is treated as urgent because it damages connected equipment. The set is taken off load before anything else is investigated.

  • Noise or heat at the alternator end

    Bearing noise, a burnt-insulation smell or heat and discolouration are mechanical and insulation findings. They are recorded even when the original complaint was electrical.

The sequence

What is tested, and in what order

The cheap and reversible checks come before anything is dismantled. A rewind is a conclusion, not a starting assumption.

  • 01

    Confirm the engine side first

    Speed and stability are established before output is judged. An engine that is not holding its governed speed will produce voltage and frequency symptoms that are not alternator faults.

  • 02

    Check breakers and connections

    An open breaker, a loose terminal or a damaged cable explains a dark board without any fault inside the machine. These are checked before the alternator is opened.

  • 03

    Measure at the terminals

    Readings are taken on the running set so the fault is described by measurement rather than by the customer’s symptom alone.

  • 04

    Test the excitation and AVR

    The regulator and its supply are assessed as a circuit. Swapping an AVR without establishing why there is no output can leave the real fault in place.

  • 05

    Assess windings and insulation

    Where the electrical tests point at the machine itself, winding condition and insulation are examined. This is what separates a repairable fault from a rewind.

  • 06

    Report, then quote

    The finding is explained and the proposed work is quoted before parts are changed. Where a part cannot be sourced for that alternator, the quote says so.

Why the alternator is a separate diagnosis

On most standby sets the engine and the alternator are built by different manufacturers. Leroy-Somer is the alternator, and the engine beside it may be Perkins, Cummins, Deutz or another make entirely. That matters when a fault is booked, because an engine that will not start and an engine that runs without producing power lead to two different visits with different equipment.

It also matters for parts. An AVR or a winding repair belongs to the alternator model on the alternator plate, not to the engine badge on the canopy. This is why a photograph of the alternator plate is more useful than the generator brand on the enclosure, and why the kVA and the alternator model are both asked for before a visit.

Where the engine itself is the problem, the work moves to diesel generator repairs. Where the set never turns over, start with generator not starting. Where it runs and the board stays dead, generator not producing power is the closer match.

Google reviews of ProService Generator Repairs

  • Google Review

    [ProService Generator Repairs] rewound our Leroy-Somer alternator and bench-tested it to exact factory specs. They replaced the diodes and AVR perfectly, saving the whole machine.

  • Google Review

    True Leroy-Somer alternator experts.

Do you repair Leroy-Somer generator alternators?

Yes. Leroy-Somer alternators fitted to generator sets are inspected and repaired independently across Gauteng. This is alternator work, not a diesel-engine brand page.

Why does the engine run and the Leroy-Somer alternator make no voltage?

No output with the engine running can be the breaker, the AVR, excitation, or the alternator windings. The engine being healthy does not prove the alternator is healthy.

Can low or unstable voltage be an AVR fault?

Yes. Low, high or unstable voltage can sit in the AVR, the excitation circuit, engine speed, wiring or the windings. The cause is confirmed before parts are replaced.

Do you rewind Leroy-Somer alternators?

Winding and insulation faults are assessed. Rewinding, when it is the right repair, is handled through the generator rewinding service. Not every electrical fault needs a rewind.

Is Leroy-Somer a diesel engine brand?

No. Leroy-Somer is treated here as an alternator manufacturer. Diesel engine brands stay on the diesel generator repairs pages.

What should I send before the visit?

A photo of the alternator plate, the generator kVA, and a description of the voltage fault. Say whether the engine starts and whether any voltage appears.

Where to go next

Voltage faults, rewinding and the engine side

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