Generator Maintenance: Alternator that unknown thing.

The alternator .. that unknown thing

Warning: The following information is reserved exclusively for qualified technical personnel who have undergone specific training on all risks related to the generator set and the risk of electrocution. Read the manuals provided by the manufacturer carefully.

Alternator, so much important though so much overlooked

One is led to think that the engine the most important working part, and that instead the alternator is nothing but two windings put in rotation, which generate electricity. But, thanks to that electrical part that the generator is defined as such because it is the alternator which is responsible for channelling  the energy the engine needs.

Mechanical controls

It often happens that our staff bother removing the fan’s protection grid or the rear shield for routine checks and customers say to me they’ve never someone removing those parts before.

From there it’s  possible to get access to the coupling/discs/rubber supports and everything that hold the coupling between the engine and the alternator. Only this way it is possible to verify the integrity of the clamping disks.

The ventilation of the alternator is through forced air which is sucked in at the rear, and after having passed through the windings it’s pushed out from the fan. Therefore, you can clean internally and free the airways by avoiding overheating only by removing it.

From the rear shield you can measure the air gap (distance between the rotor and the stator) using a special feeler gauge and comparing the values with the manufacturer's data. a decrease or increase of the air gap can easily signal an anomalous movement of the bearing.

The bearing greasing must be carried out according to the annual frequency or to  the hours worked indicated on the alternator’s plate. if you pay attention, the plate also shows the type of grease to be used.

Electrical controls


They could fall within the mechanical controls but, having to do with the power cables, it is possible to remind it now: I’m referring to the testing of the power cables placed inside the upper casing. a dedicated section of the user manual indicates the cables tightening to the power terminals.

It’s also the opportunity to check if there are signs of rust or oxidation to the terminals or if there are cracks in the insulators.

Having finished with the power cables you can check all the wires of the auxiliaries that go to the terminal board trying to be delicate with these latter especially if you are working on an old alternator. They are easy to break because of the deteriorated plastic.

Before closing everything, you will have also taken a look at the windings, using a bright lamp, so you can make sure that there are no loosening or dirt. I'll cover the "cleaning"  topic later in this article.


To avoid damage to the customer's utility, it is absolutely necessary to measure the voltage and frequency with an instrument, periodically calibrated and certified. (Calibrated and certified in accordance with a quality system)

You must verify that the no-load voltage is in the threshold values as stated on the generator's plate ( 400, 380, 230V etc) that does not deviate from the established limits. it then compares the values with those of the previous maintenance, to check if there have been variations that could anticipate a problem of the alternator's return or a voltage regulator problem.

Now you can close the alternator power box, tighten the cover bolts well and make sure that there are still stickers with a symbol for electrical danger otherwise it will be your concern to get new ones.

Our Generators are equipped with Mecc Alte ; Stamford ; Marelli ; Leroy Somer