Always powered up:

- the alternator

In our “Introducing a product” series, we give you the essential information from the experts about different vehicle technologies and equipment in a compact, uncomplicated form. Here, the focus is on the alternator.

Design and function of an alternator

Many of the functions in a vehicle require electrical power. The alternator obtains this power from the running combustion engine. In contrast, the car battery serves as a power store and buffer.

The construction and capacity of the alternator must be designed to ensure that sufficient power is available for all electrical consumers that can be operated over a longer period of time.

The alternator is usually driven by the vehicle engine via a V-ribbed belt. The turning of the rotor in the stationary stator causes the alternator to generate electrical current inductively. Most alternators are three-phase generators. A bridge rectifier with high-power diodes converts the alternating current into direct current.

Depending on the vehicle’s current power requirements, the regulator provides the exciter coil in the rotor with the necessary power. This is transferred via the carbon brushes on the controller to the slip rings on the rotor.

As a result of electromagnetic losses and the electrical resistances of the components, heat is generated in the alternator in addition to electrical output. Depending on the design, one or two fans are therefore installed on the rotor shaft to dissipate heat.

This video also shows you how an alternator works:


All from MAHLE

Following the takeover of Letrika (previously Iskra; now MAHLE Electric Drives), MAHLE Aftermarket now offers a broad product portfolio in this area for a wide variety of applications. Whether you need products for passenger cars, commercial vehicles, or agricultural and construction machinery, MAHLE can supply you with alternators and the corresponding spare parts, including voltage regulators, rectifiers, bearings, slip rings, and belt pulleys.

All of MAHLE’s alternators meet the demanding OE specifications and are designed for a long service life—even in harsh conditions. High quality and operational reliability are assured by continuously adapting the products for use in different operating conditions and thanks to numerous analyses in MAHLE’s own laboratories and in vehicles. The design of the starter motors and alternators fulfills international guidelines and standards, such as the Electromagnetic Compatibility (EMC) Directive.

Facts & figures

At the end of 2018, we added new alternators in OE quality to our range. For the ten largest manufacturers of heavy-duty commercial vehicles, MAHLE’s products cover around 80 percent of the vehicles currently on the streets.

Find more exciting MPULSE articles here:

This MPULSE article gives you >> tips about the replacement of alternators

Here you find >> installation tips

On our website you find the >> assembly instructions

Click here for the >> Technical Messenger on the topic of alternators


We regularly provide technical tips relating to the powertrain, thermal management, and mechatronics in automobiles.


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