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.
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HEV Charging Systems

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.

A BAS used on some HEVs

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.… READ THE REST

AC Generator Design Differences

All AC generators operate on the same principles, there are differences in the styles and construction.

General Motors 10SI Series

10SI AC generator

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.… READ THE REST

Charging Indicators

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.

Electronic regulator with an indicator light on due to no AC generator output

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

Ammeter connected in series to indicate charging system operation

FIGURE. Ammeter connected in series to indicate charging system operation.… READ THE REST

Regulation

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.… READ THE REST

AC Generator Operation Overview

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.… READ THE REST

AC Generator Circuits

There are three principal circuits used in an AC generator:

  1. The charging circuit: Consists of the stator windings and rectifier circuits.
  2. The excitation circuit: Consists of the rotor field coil and the electrical connections to the coil.
  3. 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.… READ THE REST