AC Generator Design Differences

10SI AC generator
All AC generators operate on the same principles, there are differences in the styles and construction. General Motors 10SI Series FIGURE. 10SI AC generator. SI series AC generators use an internal voltage regulator that is mounted to the inside of the slip ring end frame. There are three terminals on the rear-end frame of the AC generators: Terminal number Is Connects to the field through one brush and slip ring and to the output of the diode trio. In addition, this terminal is connected to a portion of the regulator and warning light circuitry. Terminal number 2: Connects to the regulator to supply battery voltage to a portion of the regulator circuitry that senses system voltage. BAT terminal: Connects to the output of the stator windings and supplies the battery with charging voltage. Most SI series AC generators use a 14-pole rotor. Depending on model, the stator is wired either in wye or delta fashion. Models 10 and 12 use the wye connection. All other models use the delta connection. General Motors CS Series Beginning in 1986 and continuing through the 1999 model year, General Motors used the smaller CS series AC generator with an internal regulator. This generator uses a delta wound stator. Hie field current is supplied directly from the stator, thus eliminating the need for a diode trio. The generators in this series include the CS-121, CS-130, and CS-144, which represent the unit size in millimeters. As mentioned earlier, recent CS series generators use computer control regulation of the AC generator. In addition to regulation control by varying the ground of the field windings, General Motors also uses a system of pulsing the voltage output to the field windings from the PCM. This type of generator has a constant field winding ground connection. FIGURE. General Motors' PCM-controlled charging system using high side pulse width control. AD200 Series AC Generators FIGURE. AD200 series generator. Beginning in 1999, General Motors began to change to a Delphi-designed AD200 series generator. The AD200 designation refers to second-generation (200), aircooled (A) and dual internal fans (D). There are three AD200 series models being used, depending on unit diameters: AD230 (130 mm), AD237 (137 mm), and AD244 (144 mm). Amperage output of these alternators ranges from 102 amps to 150 amps. The AD200 series generator uses an offset-wound stator to achieve a more consistent output voltage. Some models also use a pulley with a built-in clutch. The rectifier design has an increased surface area...

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Regulation

The regulator can control the field current by (A) controlling the resistance in series with the coil, or (B) by switching the field on and off
The battery, and the rest of the electrical system, must be protected from excessive voltages. To prevent early battery and electrical system failure, regulation of the charging system voltage is very important. Also, the charging system must supply enough current to run the vehicle's electrical accessories when the engine is running. AC generators do not require current limiters; because of their design, they limit their own current output. Current limit is the result of the constantly changing magnetic field because of the induced AC current. As the magnetic field changes, an opposing current is induced in the stator windings. This inductive reactance in the AC generator limits the maximum current that the AC generator can produce. Even though current (amperage) is limited by its operation, voltage is not. The AC generator is capable of producing as high as 250 volts, if it were not controlled. Regulation of voltage is done by varying the amount of field current flowing through the rotor. Hie higher the field current, the higher the output voltage. Control of field current can be done either by regulating the resistance in series with the field coil or by turning the field circuit on and off. By controlling the amount of current in the field coil, control of the field current and the AC generator output is obtained. To ensure a full battery charge, and operation of accessories, most voltage regulators are set for a system voltage between 13.5 and 14.5 volts. FIGURE. The regulator can control the field current by (A) controlling the resistance in series with the coil, or (B) by switching the field on and off. The regulator must have system voltage as an input in order to regulate the output voltage. The input voltage to the AC generator is called sensing voltage. If sensing voltage is below the regulator setting, an increase in charging voltage output results by increasing field current. Higher sensing voltage will result in a decrease in field current and voltage output. A vehicle being driven with no accessories on and a fully charged battery will have a high sensing voltage. The regulator will reduce the charging voltage until it is at a level to run the ignition system while trickle charging the battery. If a heavy load is turned on (such as the headlights), the additional draw will cause a drop in the battery voltage. The regulator will sense this low system voltage and...

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AC Generator Operation Overview

(A) Individual stator winding voltages; (B) voltages across the stator terminal A, B, and C
When the engine is running, the drive belt spins the rotor inside the stator windings. This magnetic field inside the rotor generates a voltage in the windings of the stator. Field current flowing through the slip rings to the rotor creates alternating north and south poles on the rotor. The induced voltage in the stator is an alternating voltage because the magnetic fields are alternating. As the magnetic field begins to induce voltage in the stator's windings, the induced voltage starts to increase. The amount of voltage will peak when the magnetic field is the strongest. As the magnetic field begins to move away from the stator windings, the amount of voltage will start to decrease. Each of the three windings of the stator generates voltage, so the three combine to form a three-phase voltage output. In the wye connection, output terminals (A, B, and C) apply voltage to the rectifier. Because only two stator windings apply voltage (because the third winding is always connected to diodes that are reverse-biased), the voltages come from points A to В, В to C, and С to A. FIGURE. (A) Individual stator winding voltages; (B) voltages across the stator terminal A, B, and C. To determine the amount of voltage produced in the two stator windings, find the difference between the two points. For example, to find the voltage applied from points A and B, subtract the voltage at point В from the voltage at point A. If the voltage at point A is 8 volts positive and the voltage at point В is 8 volts negative, the difference is 16 volts. This procedure can be performed for each pair of stator windings at any point in time to get the sine wave patterns. The voltages in the windings are designated as Va, Vb, and Vc. Designations of Vab, Vbc, and Vca refer to the voltage difference in the two stator windings. In addition, the numbers refer to the diodes used for the voltages generated in each winding pair. Note: Alternating current is constantly changing, so this formula would have to be performed at several different times. The current induced in the stator passes through the diode rectifier bridge, consisting of three positive and three negative diodes. At this point, there are six possible paths for the current to follow. The path that is followed depends on the stator terminal voltages. If the voltage from points A and В...

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AC Generator Circuits

The diode trio connects the phase windings to the field. To conduct, there must be 0.6 V more positive on the anode side of the diodes
There are three principal circuits used in an AC generator: The charging circuit: Consists of the stator windings and rectifier circuits. The excitation circuit: Consists of the rotor field coil and the electrical connections to the coil. The preexcitation circuit: Supplies the initial current for the field coil that starts the buildup of the magnetic field. For the AC generator to produce current, the field coil must develop a magnetic field. Hie AC generator creates its own field current in addition to its output current. For excitation of the field to occur, the voltage induced in the stator rises to a point that it overcomes the forward voltage drop of at least two of the rectifier diodes. Before the diode trio can supply field current, the anode side of the diode must be at least 0.6 volt more positive than the cathode side. When the ignition switch is turned on, the warning lamp current acts as a small magnetizing current through the field. This current preexcites the field, reducing the speed required to start its own supply of field current. Note: If the battery is completely discharged, the vehicle cannot be push started because there is no excitation of the field coil. FIGURE. The diode trio connects the phase windings to the field. To conduct, there must be 0.6 V more positive on the anode side of the diodes. FIGURE. Schematic of a charging system.

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AC Generators

Components of an AC generator
Note: The first charging systems used a DC generator that had two field coils that created a magnetic field. Output voltage was generated in the wire loops of the armature as it rotated inside the magnetic field. Current sent to the battery was through the commutator and the generator's brushes. FIGURE. Components of an AC generator. The DC generator was unable to produce the sufficient amount of current required when the engine was operating at low speeds. With the addition of more electrical accessories and components, the AC (alternating current) generator, or alternator, replaced the DC generator. The main components of the AC generator are: The rotor. Brushes. The stator. The rectifier bridge. The housing. Cooling fan. Rotors FIGURE. Components of a typical AC generator rotor. The rotor creates the rotating magnetic field of the AC generator. It is the portion of the AC generator that is rotated by the drive belt. The rotor is constructed of many turns of copper wire around an iron core. There are metal plates bent over the windings at both ends of the rotor windings. The poles (metal plates) do not come into contact with each other, but they are interlaced. When current passes through the coil (1.5 to 3.0 amperes), a magnetic field is produced. The strength of the magnetic field is dependent on the amount of current flowing through the coil and the number of windings. FIGURE. The north and south poles of a rotor's field alternate. The poles will take on the polarity (north or south) of the side of the coil they touch. The right-hand rule will show whether a north or south pole magnet is created. When the rotor is assembled, the poles alternate from north to south around the rotor. As a result of this alternating arrangement of poles, the magnetic flux lines will move in opposite directions between adjacent poles. This arrangement provides for several alternating magnetic fields to intersect the stator as the rotor is turning. These individual magnetic fields produce a voltage by induction in the stationary stator windings. FIGURE. Magnetic flux lines move in opposite directions between the rotor poles. The wires from the rotor coil are attached to two slip rings that are insulated from the rotor shaft. The slip rings function much like the armature commutator in the starter motor, except they are smooth. The insulated stationary carbon brush passes field current into a slip ring, then through the field coil,...

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Integrated Starter Generator

A BAS mounted external to the engine
One of the newest technologies to emerge is the ⚡ integrated starter generator ⚡ (ISG). Although this system can be used in conventional engine-powered vehicles, one of the key contributors to the Hybrid's fuel efficiency is its ability to automatically stop and restart the engine under different operating conditions. A typical Hybrid vehicle uses a 14 kilowatt (kW) electric induction motor or ISG between the engine and the transmission. The ISG performs many functions such as fast, quiet starting, automatic engine stops/starts to conserve fuel, recharges the vehicle batteries, smoothes driveline surges, and provide regenerative braking. The ISG is a three-phase AC motor. At low vehicle speeds, the ISG provides power and torque to the vehicle. It also supports the engine, when the driver demands more power. During vehicle deceleration, ISG regenerates the power that is used to charge the traction batteries. The ISG can also convert kinetic energy from AC to DC voltage. When the vehicle is traveling downhill and there is zero load on the engine, the wheels can transfer energy through the transmission and engine to the ISG. The ISG then sends this energy to the HV battery for storage. FIGURE. A BAS mounted external to the engine. An ISG can be mounted externally to the engine and connected to the crankshaft with a drive belt. This design is called a belt alternator starter (BAS). In these applications, the unit can function as the engine's starter motor as well as a generator driven by the engine. Both the BAS and the ISG use the same principle to start the engine. Current flows through the stator windings it generates magnetic fields in the rotor. This will cause the rotor to turn, thus turning the crankshaft and starting the engine. In addition, this same principle is used to assist the engine as needed when the engine is running.

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