Charging Systems: Summary

The most common method of stator connection is called the wye connection. In the wye connection, one lead from each winding is connected to one common junction. From this junction, the other leads branch out in a Y pattern. Another method of stator connection is called the delta connection. The delta connection connects the lead of one end of the winding to the lead at the other end of the next winding. The diode rectifier bridge provides reasonably constant DC voltage to the vehicle's electrical system and battery. Hie diode rectifier bridge is used to change the current in an AC generator. The converting of AC current to DC current is called rectification. The three principal circuits used in the AC generator are the charging circuit, which consists of the stator windings and rectifier circuits; the excitation circuit, which consists of the rotor field coil and the electrical connections to the coil; and the preexcitation circuit, which supplies the initial current for the field coil that starts the buildup of the magnetic field. The voltage regulator controls the output voltage of the AC generator, based on charging system demands, by controlling field current. The higher the field current, the higher the output voltage. The regulator must have system voltage as an input in order to regulate the output voltage. The input voltage to the regulator is called sensing voltage. Because ambient temperatures influence the rate of charge that a battery can accept, regulators are temperature compensated. The A circuit is called an external grounded field circuit and is always an electronic-type regulator. In the A circuit, the regulator is on the ground side of the field coil. The B+ for the field coil is picked up from inside the AC generator. Usually the В circuit regulator is mounted externally of the AC generator. The В circuit is an internally grounded circuit. In the В circuit, the voltage regulator controls the power side of the field circuit. Isolated field AC generators pick up B+ and ground externally. The AC generator has two field wires attached to the outside of the case. The voltage regulator can be located either on the ground (A circuit) or on the B+ (B circuit) side. An electronic regulator uses solid-state circuitry to perform the regulatory functions using a zener diode that blocks current flow until a specific voltage is obtained, at which point it allows...

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HEV Charging Systems

A BAS used on some HEVs
HEVs utilize the automatic stop/start feature to shut off the engine whenever the vehicle is not moving or when power from the engine is not required. Some HEV systems use a starter/generator unit to perform both functions. The difference between a motor and a generator is the motor uses two opposing magnetic fields and the generator uses one magnetic field that has rotating conductors. The use of electronics to control the direction of current flow allows the unit to function as both a motor and a generator. FIGURE. A BAS used on some HEVs. There are two basic designs of the starter/generator. Hie first design uses a belt alternator starter (BAS) that is about the same size as a conventional generator and is mounted in the same way. The second design is to mount an integrated starter/generator (ISG) at either end of the crankshaft. Most designs have the ISG mounted at the rear of the crankshaft between the engine and transmission. FIGURE. The ISG is usually located at the rear of the crankshaft in the bell housing. The ISG is a 3-phase AC motor that can provide power and torque to the vehicle. It also supports the engine, when the driver demands more power. As seen in Figure, the ISG includes a rotor and stator that is located inside the transmission bell housing. The stator is attached to the engine block and is made up of two separate lamination stacks. The rotor is bolted to the engine crankshaft and has both wire wound and permanent magnet sections. Rectification is accomplished with traditional diodes. The advantage of this rotor and stator design is that the output at engine idle speed is up to 240 amps. Maximum output can exceed 300 amps. Generation is done anytime the engine is running. Since the rotor is connected to the crankshaft, it turns at the speed of the engine. Also, during vehicle deceleration the ISG regenerates the power that is used to slow the vehicle to recharge the HV and auxiliary batteries. 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 energy (AC voltage) is converted to DC voltage and sent to the batteries for storage and use by the electrical components of the vehicle. Remember that the output of conventional AC generators is dependent upon the intensity of the magnetic field, the...

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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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Charging Indicators

Electronic regulator with an indicator light on due to no AC generator output
There are three basic methods of informing the driver of the charging system's condition: indicator lamps ammeter voltmeter Indicator Light Operation As discussed earlier, most indicator lamps operate on the basis of opposing voltages. If the AC generator output is less than battery voltage, there is an electrical potential difference in the lamp circuit and the lamp will light. If there is no stator output through the diode trio, then the lamp circuit is completed to ground through the rotor field and TR1. FIGURE. Electronic regulator with an indicator light on due to no AC generator output. On most systems, the warning lamp will be "proofed" when the ignition switch is in the RUN position before the engine starts. This indicates that the bulb and indicator circuit are operating properly. Proofing the bulb is accomplished because there is no stator output without the rotor turning. Ammeter Operation FIGURE. Ammeter connected in series to indicate charging system operation. In place of the indicator light, some manufacturers install an ammeter. The ammeter is wired in series between the AC generator and the battery. Most ammeters work on the principle of d'Arsonval movement. FIGURE. Ammeter needle movement indicates charging conditions. The movement of the ammeter needle under different charging conditions is illustrated. If the charging system is operating properly, the ammeter needle will remain within the normal range. If the charging system is not generating sufficient current, the needle will swing toward the discharge side of the gauge. When the charging system is recharging the battery, or is called on to supply high amounts of current, the needle deflects toward the charge side of the gauge. It is normal for the gauge to read a high amount of current after initial engine startup. As the battery is recharged, the needle should move more toward the normal range. Voltmeter Operation FIGURE. Voltmeter connected to the charging circuit to monitor operation. Because the ammeter is a complicated gauge for most people to understand, many manufacturers use a voltmeter to indicate charging system operation. In early systems, the voltmeter is connected between the battery positive and negative terminals. When the engine is started, it is normal for the voltmeter to indicate a reading between 13.2 and 15.2 volts. If the voltmeter indicates a voltage level that is below 13.2, it may mean that the battery is discharging. If the voltmeter indicates a voltage reading that is above 15.2 volts, the charging system is overcharging the battery. The battery and electrical...

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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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