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. 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.

General Motors' PCM-controlled charging system using high side pulse width control

FIGURE. General Motors’ PCM-controlled charging system using high side pulse width control.

AD200 Series AC Generators

AD200 series generator

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 and uses avalanche diodes.

Ford AC Generators

Flat-type rectifier has single plate containing all six diodes

FIGURE. Flat-type rectifier has single plate containing all six diodes.

Ford has used several different designs of AC generators. For many years, Ford used the common rear- or side-terminal AC generator. The rear-terminal AC generators used two different types of rectifiers. One rectifier had a single plate that contained all six of the diodes.

The second type of rectifier used two plates that were stacked on top of each other. One plate contained the positive diodes and the other contained the negative diodes.

On the rear-terminal AC generators there were four terminals on the end frame:

  • BAT terminal: Stator output connection to the battery.
  • FLD terminal: Connection to one side of the field winding through the insulated brush and the slip ring.
  • STA terminal: Connection to the neutral stator junction.
  • GRD terminal: Connection for the ground wire from the regulator.

The Ford side terminal AC generator is larger and has higher output capacities. The same four terminals are used; however, they are arranged differently.

In 1984, Ford introduced an integral alternator regulator (IAR) AC generator. The regulator is mounted on the exterior of the rear-end frame, which simplifies testing and replacement of the regulator. The F and A terminals are used to test the charging system. Additional modifications include the brushes being a part of the regulator.

When the ignition switch is in the RUN position, voltage is sent to the I terminal of the regulator. Regulator terminal A senses system voltage. Field current is drawn through this terminal also.

IAR charging system schematic

FIGURE. IAR charging system schematic.

Ford’s EVR charging system uses a solid-state external regulator. This style is built with either rear or side terminals. Hie side-terminal design provides higher output by using delta wound stators.

Chrysler AC Generators

Early Chrysler AC generators used separate heat sinks for the positive and negative diodes. Both heat sinks are attached to the rear-end frame. Also, the brushes are attached to the exterior of the end frame. This allows for brush replacement without having to disassemble the AC generator (in fact, the brushes can usually be replaced without having to remove the AC generator from the vehicle).

The three terminals on the rear-end frame are connected as follows:

  • BAT terminal: Connects the stator output to the battery to supply charging voltage.
  • FLD terminal: There are two field terminals. Battery voltage is applied to one of the field terminals; the regulator connects to the second field terminal.

Computer-controlled dual-output charging system

FIGURE. Computer-controlled dual-output charging system.

In 1985, Chrysler introduced a delta wound, dual-output, computer-controlled charging system. This system has some unique capabilities:

  1. The system is capable of varying charging system output based on the ambient temperature and the system’s voltage needs.
  2. The computer monitors the charging system and is capable of self-diagnosis.

When the ignition switch is in the RUN position, the PCM checks the ambient temperature and determines required field current. Based on inputs relating to temperature and system requirements, the PCM determines when current output adjustments are required.

In recent years, Chrysler used a Nipponclenso or Bosch-built AC generator that has a wye wound stator. This system also uses a PCM, to control voltage regulation by varying the field winding ground. Vehicles equipped with next-generation controllers (NGC) have high side control, similar to that of General Motors CS series discussed earlier.

Mitsubishi AC Generators

Mitsubishi AC generator terminals

FIGURE. Mitsubishi AC generator terminals.

Some Mitsubishi AC generators use an internal voltage regulator. It also has two separate wye connected stator windings. Each of the stator windings has its own set of six diodes for rectification.

The Mitsubishi AC generator uses two separate stator windings and a total of 15 diodes

FIGURE. The Mitsubishi AC generator uses two separate stator windings and a total of 15 diodes.

This AC generator also uses a diode trio to rectify stator voltage to be used in the field winding. The three terminals are connected as follows:

  • В terminal: Connects the output of both stator windings to the battery, supplying charging voltage.
  • R terminal: Supplies 12 volts to the regulator.
  • L terminal: Connects to the output of the diode trio to provide rectified stator voltage to designated circuits.

Schematic of Mitsubishi charging system using both an internal voltage regulator and the PCM to control output

FIGURE. Schematic of Mitsubishi charging system using both an internal voltage regulator and the PCM to control output.

Another method that Mitsubishi uses for charging control involves a single wye wound stator generator with an internal regulator that interfaces with the PCM. The PCM monitors the state of the field coil through terminal FR of the generator. The PCM sends 5 volts to the FR terminal. As the field coil is turned on and oft by the internal regulator, the voltage will cycle between 5 and 0 volts. When the PCM senses 5 volts, it knows the field coil is turned off, and when the voltage drops close to 0 volts, it knows the field coil is turned on. This allows the PCM to control idle speed when the regulator is applying full field. In addition, the PCM can dampen the effects of full fielding during high electrical loads. This will prevent occurrences such as lights flicking bright and dim as the field coil is turned on and off.

When a full field condition is sensed by the PCM, it will modulate its internal transistor. This will then control the power transistor in the internal regulator. The PCM has a maximum authority of 14.4 volts. If the charging system output exceeds this level, the internal regulator turns the power transistor off.

To perform this function, the PCM will duty cycle its internal transistor, which turns the TR1 in the generator on and off. In Figure, battery voltage is applied to the S terminal of the generator. This voltage goes through three resistors in series to ground. Each of the resistors has 2 ohms of resistance. If the PCM internal transistor is turned on, the voltage to the base of TRt is pulled low and TR1 is turned off. With TR, turned off, all three of the resistors are involved in the circuit. Each resistor will drop 4 volts. Since R1 drops 4 volts, 8 volts is applied to the zener diode. This is enough to blow through the diode, applying voltage to the base of TR, and turning it on. With TR2 turned on, base voltage to transistor TR3 is pulled low and transistor TR3 will be turned off. With TR3 turned off, the field coil is de-energized.

Three resistors in series on the sense circuit

FIGURE. Three resistors in series on the sense circuit.

If the internal transistor in the PCM is turned off, battery voltage will be applied to the base of TR, and turn it on. TR, will now supply an alternate path to ground, bypassing R3.

Now, only R1 and R2 are in series and each resistor will drop 6 volts. This means that 6 volts will be applied to the zener diode. This is not enough to blow through the zener; therefore, TR2 will be off. With TR2 off, battery voltage is applied to the base of transistor TR3 and it will be turned on. Since transistor TR3 is on, the field coil circuit to ground is complete and the coil is energized. The PCM internal transistor switches on and off several times a second to prevent the generator from going to full field too rapidly.

Brushless AC Generators

Brushless AC generator with stationary field and stator windings

FIGURE. Brushless AC generator with stationary field and stator windings.

Some manufacturers have developed AC generators that do not require the use of brushes or slip rings. In these AC generators, the field winding and the stator winding are stationary. A screw terminal is used to make the electrical connection. Hie rotor contains the pole pieces and is fitted between the field winding and the stator winding.

The magnetic field is produced when current is applied to the field winding. The air gaps in the magnetic path contain a nonmetallic ring to divert the lines of force into the stator winding.

The pole pieces on the rotor concentrate the magnetic field into alternating north and south poles. When the rotor is spinning, the north and south poles alternate as they pass the stator winding. The moving magnetic field produces an electrical current in the stator winding. The alternating current is rectified in the same manner as in conventional AC generators.