Parts of an Alternator – Labeled Diagram with Names

All 15 parts on the diagram

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Cut open along the shaft 11

Rotor The belt turns it. Current in its winding makes it a magnet, and its turning field sweeps past the stator.
Stator A ring of thin iron plates with slots for the windings. The alternator's output is made here.
Stator windings Three sets, so the alternator makes three alternating currents at once. You see the loops where they stick out of the ring.
Pulley The engine's belt turns it, and it turns the rotor.
Fan This one is outside the case, just behind the pulley. Newer alternators have their fans inside.
Brushes They carry a small current to the spinning rotor. Springs in the holder keep them pressed on.
Rectifier Its diodes let current pass one way only. That turns the stator's alternating current into the direct current a car uses. It is also called the rectifier bridge or diode bridge.
Voltage regulator It does that by changing the current sent to the rotor's winding. This one is inside the case; some cars have it as a separate box.
Bearings There is one in each end of the case.
Drive end frame It carries the front bearing. Some books call it the front housing.
Slip ring end frame It carries the rear bearing, the brushes and the rectifier. Some books call it the rear housing.

The rotor, taken apart 4

Pole pieces Each has fingers that fit between the fingers of the other. One half becomes north poles and the other south poles.
Field winding It sits between the two pole pieces. Current through it is what makes them magnets.
Slip rings Each is joined to one end of the field winding. The brushes ride on them.
Rotor shaft The pole pieces hold the field winding between them on it. The pulley goes on its other end.

How this list was compiled: Part names checked on 2026-09-30; a name is kept only when two independent sources use it. (1) US Army TM 9-8000, Principles of Automotive Vehicles, 1985, chapter 13, paragraphs 13-21 to 13-29 and figures 13-21, 13-22 and 13-25, https://archive.org/details/tm-9-8000-principles-of-automotive-vehicles-1985 (rotor, stator of a slotted laminated ring, three stator windings, pole pieces with finger-like projections, field winding on the shaft, slip rings, brushes, rectifier bridge of six diodes, drive end frame, slip ring end frame, bearing, fan, voltage regulator). (2) Missouri Auto Mechanics Curriculum Guide, Module 2, Electrical Systems, University of Missouri, 1989, https://archive.org/details/micro_IA41155136_1005 (drive pulley, fan, rotor, north and south pole pieces, field winding, slip rings, brushes and brush holder, stator windings, laminated iron core, diode bridge, rectifier assembly, bearings, front and rear housings, drive-end frame, internal regulator within the alternator housing). (3) Florida Automotive Mechanics Curriculum, Engine Tune-Up Service, Unit 2, Charging System, student guide, Florida State University, 1978, https://archive.org/details/micro_IA41153762_0988 (alternator pulley, rotor assembly, stator assembly, diodes, drive end frame, slip ring end frame, regulator as a separate unit). (4) Wikipedia, Alternator (automotive), text only (rotor with claw-pole pieces, stator, slip rings, brushes, rectifier diodes, belt and pulley, fan on the pulley and later fans inside the casing, shaft bearings, regulator). Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; no maker's alternator, nothing traced. Licence: own work

How it works

The parts of an alternator turn some of the engine's motion into electricity, to charge the battery and run the car's electrical system. This one is cut through along its shaft, pulley on the left.

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The belt turns the pulley, and the pulley turns the rotor inside the stator. The rotor is a spinning magnet, and it makes current flow in the stator windings. That current is alternating, so the rectifier's diodes turn it into direct current. The voltage regulator keeps the voltage steady. The case is two end frames with a bearing in each, and the fan cools it.

The rotor, taken apart

Two pole pieces hold the field winding between them on the rotor shaft, and their fingers fit between each other. The brushes feed current to the winding through the two slip rings.

Rotor turns, stator stays: the names say which is which.
An older car's generator makes its current in the turning part. An alternator makes it in the part that stands still.

Questions and answers

What are the parts of an alternator?

A pulley and fan on the front, two end frames with a bearing in each, a stator with its windings, a rotor made of two pole pieces and a field winding, slip rings, brushes, a rectifier and a voltage regulator.

What is the difference between the rotor and the stator?

The rotor spins and the stator does not. The rotor is the magnet: current in its field winding makes its pole pieces north and south poles. The stator is the ring of windings round it, where the output current is made.

What does the rectifier do in an alternator?

It turns alternating current into direct current. Its diodes let current flow one way only. Most car alternators have three stator windings, so the rectifier has six diodes, three positive and three negative.

Why does an alternator have brushes?

To carry current to the spinning field winding, through the slip rings. They carry only that small current, not the alternator's whole output, so they can be small.