Alternator

Alternators are so named because they produce alternating current. It is sometimes more desireable to produce alternating current because it is a mechanically simpler thing to do. You can simply rotate a permanent magnet in a set of field coils, rather than having to rotate the coils in a magnetic field, requiring a commutator.

There are many different kinds of alternators, ranging from the tiny one in your car to the giant ones at your local power plant. Depending on how many poles an alternator has, it will produce that many number of phases. Three-phase power is produced using a three-pole alternator with each pole at 120 degrees.

The rotation rate of an alternator must remain constant if the current produced is to have a constant frequency. This isn't an issue in your car, since the power is rectified and filtered by the battery anyway, but in a power plant, all the power produced must be 60Hz (or 50hz if you're not in the United States). Thus, an alternator in this sort of duty has two modes: Spinning at the correct speed, or off. Thus, overloading is a bad idea, since the more energy consumed, the more torque is required to maintain a specific rotation rate. Alternators in mains duty tend to have familiar rotation rates, such as 1800 or 3600 RPM. Note that these rates divide evently into 60.

Alternating current is handy because you can voltage-convert it efficiently using transformers. If you want direct current, you can employ a dynamo.

The part of a car engine which generates the electricity required by the car, for such things as the ignition system, headlights, the stereo, etc. The bearings and the regulator are common points of failure. You can attach an alternator to a lawn mower engine to construct a makeshift emergency generator.

The charging system for an automobile has three major components: the battery, alternator, and the regulator.

The alternator works together with the battery to supply power when the vehicle is running. The output of an alternator is direct current, however, AC voltage is actually created and then converted to DC as voltage leaves the alternator on its way to the battery and the electrical loads.

Four wires connect the alternator to the rest of the charging system:
B is the alternator output wire that supplies current to the battery.
IG is the ignition input that turns on the alternator/regulator assembly.
S is used by the regulator to monitor charging voltage at the battery.
L is the wire the regulator uses to ground the charge warning lamp.

Alternator Terminal ID's:
S terminal - Senses battery voltage
IG terminal - Ignition switch signal turns regulator ON
L terminal - Grounds warning lamp
B terminal - Alternator output terminal
F terminal - Regulator Full-Field bypass

The alternator contains: A rotating field winding called the rotor; a stationary induction winding called the stator; a diode assembly called the rectifier bridge; a control device called the voltage regulator; and two internal fans to promote air circulation.

Most regulators are on the inside the alternator. Older models have externally mounted regulators. On some models, the rear cover can be removed to expose internal parts, making it easy to service from the rear of the unit. (And I can hear what you’re saying about that sentence, so DON’T! – s.) However, today's practice is to correctly diagnose the problem and replace the alternator as a unit, should one of its internal components fail.

Drive Pulley
Alternator drive pulleys either bolt on or are pressed on the rotor shaft. Both 'V' and Multi-grove types are used. Some alternators do not have external fans as part of the pulley assembly, while many manufacturers do use a external fan for cooling. Some alternators even have two internal fans to draw air in for cooling. (You’ll have to wing it! – s.)

Inside the Alternator
Removal of the rear cover reveals: the regulator which controls the alternator output; the brushes that conduct current to the rotor field winding; the rectifier bridge to convert AC voltage to DC voltage; the slip rings (part of the rotor assembly) connected to each end of the field winding; two stationary carbon brushes ride on two rotating slip rings (Brushes are either soldered or bolted.); two slip rings are located on one end of the rotor assembly. Each end of the rotor field winding is attached to a slip ring, thereby allowing current to flow through the field winding.

Electronic IC Regulator
The regulator is the brain of the charging system. It monitors both battery and stator voltages and depending on the measured voltages, the regulator will adjust the amount of rotor field current to control alternator output. Regulators can be mounted both internal or external. Current technology uses an internal regulator. (Just like my grandfather’s heart! – s.)

Diode Rectifier
The diode rectifier bridge is responsible for the conversion or rectification of AC voltage to DC voltage. Six or eight diodes are used to rectify the AC stator voltage to DC voltage. Half of these diodes are use on the positive side and the other half are on the negative side.

Inside the Alternator
Separating the case reveals: the rotor winding assembly rotates inside the stator winding. The rotor generates a magnetic field; the stator winding develops voltage and current begins to flow from the induced magnetic field of the rotor.

Rotor Assembly
A basic rotor consists of an iron core, coil winding, two slip rings, and two claw-shaped finger pole pieces. Some models include support bearings and one or two internal cooling fans. The rotor is driven or rotated inside the alternator by an engine (alternator) drive belt. The rotor contains the field winding wound over an iron core which is part of the shaft. Surrounding the field coil are two claw-type finger poles. Each end of the rotor field winding is attached to a slip ring. Stationary brushes connect the alternator to the rotor. The rotor assembly is supported by bearings. One on the shaft the other in the drive frame.

Alternating Magnetic Field
The rotor field winding creates the magnetic field that induces voltage into the stator. The magnetic field saturates the iron finger poles. One finger pole becomes a north pole and the other a south pole. The rotor spins creating an alternating magnetic field, North, South, North, South, etc.

As the rotor assembly rotates within the stator winding, the alternating magnetic field from the spinning rotor induces an alternating voltage into the stator winding. The strength of the magnetic field and the speed of the rotor affect the amount of voltage induced into the stator.

Stator Windings
The stator is made with three sets of windings. Each winding is placed is a different position compared with the others. A laminated iron frame concentrates the magnetic field. Stator lead ends output current to the diode rectifier bridge. Neutral junction in the Wye design can be identified by the 6 strands of wire.

3-Phase Windings
The stator winding has three sets of windings. Each is formed into a number of evenly spaced coils around the stator core. The result is three overlapping single phase AC sine wave current signatures, A, B, C. Adding these waves together make up the total AC output of the stator. This is called three phase current. Three phase current provides a more even current output.

Stator Designs
Delta wound stators can be identified by having only three stator leads, and each lead will have the same number of wires attached.

Wye style has four stator leads. One of the leads is called the Neutral Junction. The Neutral Junction is common to all the other leads. Wye wound stators have three windings with a common neutral junction. They can be identified because they have 4 stator lead ends. Wye wound stators are used in alternators that require high voltage output at low alternator speeds. Two windings are in series at any one time during charge output.

Delta wound stators can be identified because they have only three stator lead ends. Delta stators allow for higher current flow being delivered at low RPM. The windings are in parallel, rather than in series as like the Wye design.

Rectifier Operation
The diode rectifier bridge is responsible for the conversion or rectification the AC voltage into DC voltage. Two diodes are connected to each stator lead. One positive the other negative. (Because a single diode will only block half the AC voltage.) Six or eight diodes are used to rectify the AC stator voltage to DC voltage.

Diodes
Diodes are used as one-way electrical check valves. Passing current in only one direction, never in reverse. Diodes are mounted in a heat sink to dissipate the heat generated by the diodes. Diodes redirect the AC voltage into DC voltage, so the battery receives the correct polarity.

Voltage Regulation
The regulator will attempt to maintain a pre-determined charging system voltage level. When charging system voltage falls below this point, the regulator will increase the field current, thus strengthening the magnetic field, which results in an increase of alternator output. When charging system voltage raises above this point, the regulator will decrease field current , thus weakening the magnetic field, and results in a decrease of alternator output.

Regulator Types:
Two regulator designs can be used. The first type is the grounded regulator type. The regulator controls the amount of battery ground (negative) going to the field winding in the rotor. The second type is the grounded field type. The regulator controls the amount of Battery Positive (B+) going to the field winding in the rotor.

Working Alternator
The regulator monitors battery voltage.
The regulator controls current flow to the rotor assembly.
The rotor produces a magnetic field.
Voltage is induced into the stator.
The rectifier bridge converts AC stator voltage to DC output for use by the vehicle.



This has been a completion of a quest set up by NatchLucid. I hope that you learned something about this on the way, I know *I* did! - siouxsie

Al"ter*na`tor (?), n. (Elec.)

An electric generator or dynamo for producing alternating currents.

 

© Webster 1913