Spare parts
Generator Alternators & Rewinds
The alternator is the component that turns engine power into electricity, and the decision that matters is usually rewind or replace, which depends on the size of the set.
Symptoms
- No output after the AVR has been ruled out
- Burning smell from the alternator end
- Output on some phases and not others
- Insulation resistance reading low
- Set had been running badly overloaded
What the alternator does and why it dies
The engine makes mechanical power; the alternator turns it into electricity. It is one of the two most expensive components on a generating set, and it fails for reasons that are almost always environmental rather than random.
Sustained overload. A set run continuously above its rating cooks its windings. The insulation degrades, the resistance readings drift, and eventually a winding shorts.
Moisture. A set that stands idle in a cold, wet place absorbs moisture into the windings. This is why alternator faults cluster in Limuru and Tigoni and on sets that run once a quarter. An anti-condensation heater and regular running prevent it.
Heat. A plant room that cannot move air keeps the alternator above its design temperature indefinitely.
Rotating rectifier failure. Where fitted, a failed diode can take windings with it.
Rewind or replace, with the arithmetic shown
Below about 15 kVA, the honest answer is usually replace. A complete 10 kVA silent diesel set lists around KES 190,000, and a serious alternator repair on a machine of that size can approach a significant fraction of that for an outcome that is still an old set.
Above 20 kVA, where sets are industrial plant at KES 970,000 and up, a rewind on a quality alternator is comfortably the better economics.
We price both and show you the two numbers. What we will not do is quote a rewind on a small imported set without telling you a new machine is comparable.
Fixing the cause as well as the part
A new alternator installed into the same overloaded, unventilated, damp conditions fails the same way. If the diagnosis finds sustained overload, the honest recommendation includes the sizing conversation, even though that is a larger and less welcome discussion than a part.
FAQ
▸Should I rewind or replace an alternator?
It depends on size. Below about 15kVA a complete replacement set often costs less than a serious alternator repair, because imported machines in that band are inexpensive. Above it, a quality alternator is worth rewinding and a new machine is a large capital item. We price both rather than assume.
▸Why did my alternator fail?
Most often sustained overload, moisture in the windings after long idle periods, or heat from poor plant-room ventilation. Occasionally a rotating rectifier failure takes the windings with it. The cause matters, because fitting a new alternator into the same conditions produces the same failure.
▸How long does a rewind take?
It is bench work, so days rather than hours, and longer if the winding data has to be recovered from the machine itself. We say which at diagnosis.