A generator alternator repair is needed when the engine runs perfectly but there is no voltage, low voltage or voltage that swings and damages appliances. The alternator is the electrical half of the generator: the rotor, stator windings, exciter, rotating diodes and the AVR (automatic voltage regulator) that keeps output steady at 230 V or 400 V. Tell us about the set and the fault, and we pass your request to independent auto-electricians, rewinders and generator technicians who quote you directly. We do not do the work ourselves.
Generator no voltage output
When a generator gives no voltage, technicians test from simple to serious:
- Breakers, output sockets and loose connections in the terminal box
- Brushes and slip rings on brushed alternators, which wear and stick
- Loss of residual magnetism, common after long storage, fixed by flashing the field
- Rotating diodes on brushless alternators, which short after a surge or overload
- The AVR itself, then the exciter and main windings
AVR replacement and voltage problems
A failing AVR shows up as high voltage that blows globes and chargers, low voltage that makes motors hum, or voltage that hunts with the load. Lightning, back-feeding from the mains through a wrong connection and running a set with a bad earth all kill AVRs. An AVR replacement must be matched to the alternator, and the voltage set with a meter afterwards. Good earthing, correct changeover switching and an automatic transfer switch with proper interlocks protect the alternator from mains back-feed.
Alternator rewinding and diesel generator alternators
Burnt or shorted windings, usually from sustained overloading or water ingress, can be rewound. The stator or rotor is stripped, rewound with new copper wire, varnished and baked, then tested for insulation resistance. A rewind makes most sense on diesel generator alternators from about 10 kVA up, where a new alternator end is expensive. Rodents, dust and coastal salt air are common causes, so keep the canopy clean and the louvres screened. For engine faults on the same set, see diesel generator repairs.
Alternator repair prices
Brushes cost R300 to R900 fitted, a diode set R600 to R2,500 and an AVR R900 to R3,500 for smaller sets, more for large three phase alternators. Rewinding typically costs R4,000 to R15,000 for 5 to 30 kVA, and much more for big industrial machines. Rewinds take three to ten working days. Ask for the insulation resistance reading after the repair, and keep the old AVR model number handy, since matching it exactly saves time when ordering a replacement.
What to include in your request
- Give the kVA, phase and brushed or brushless if known
- Say what the voltage reads, if you measured it
- Mention any lightning, overload or back-feed event
- Say whether the alternator can be removed and brought in
- Add photos of the rating plate and terminal box
Generator Alternator Repairs for different sites
- Homes: a standby set that runs but gives no voltage after a lightning storm
- Estates and complexes: a shared diesel set whose AVR has failed and is blowing gate motor boards
- Farms and smallholdings: a diesel generator alternator burnt out from running a borehole pump beyond its rating
- Shops, offices and restaurants: a canopied set with low voltage that makes fridges and compressors hum
- Factories, mines and sites: large three phase alternators needing diode, AVR or full rewinding work
- Lodges, venues and events: a lodge generator with fluctuating voltage that trips guests' appliances
- Clinics, schools and towers: a pump station or tower set with no output after rodents damaged the windings
Frequently asked questions
Does your site rewind alternators?
Can I test my generator's voltage myself?
Why did my generator lose voltage after standing for months?
Is kVA the same as kW on my generator?
Generator Alternator Repairs by province and city
- Johannesburg
- Pretoria
- Centurion
- Midrand
- Sandton
- Randburg
- Roodepoort
- Krugersdorp
- Randfontein
- Germiston
- Boksburg
- Benoni
- Kempton Park
- Alberton
- Vanderbijlpark
- Vereeniging
- eMalahleni (Witbank)
- Middelburg
- Secunda
- Mbombela (Nelspruit)
- Rustenburg
- Brits
- Klerksdorp
- Potchefstroom
- Mahikeng
- Polokwane
- Tzaneen
- Kimberley
- Upington
- Bloemfontein
- Welkom
- Sasolburg
- Durban
- Pinetown
- Pietermaritzburg
- Richards Bay
- Newcastle
- Ladysmith
- Gqeberha (Port Elizabeth)
- East London
- Kariega (Uitenhage)
- Mthatha
- Cape Town
- Bellville
- Paarl
- Stellenbosch
- George
- Worcester