Purpose of The Charging System
The purpose of the charging system is to convert the mechanical energy of the engine into electrical energy that is used to recharge the battery and power the electrical accessories. When the engine is first started, the battery(s) supplies all the current required by the starting and ignition systems.
As the battery drain continues and engine speed increases the charging system is able to produce more voltage than the battery can deliver. When this occurs, the electrons from the charging device are able to flow in a reverse direction through the battery's positive terminal. The charging device now supplies the electrical system's load requirements and recharges the battery.
The charging system consists of
- Battery.
- Generator.
- Drive Belt.
- Rectifier Assembly.
- Voltage Regulator.
- Charge Indicator.
- Ignition Switch.
- Cables and Wiring Harness
Scheme 80
Battery
The Battery is the primary EMF source in the automobile. The automotive battery is an electromechanical device that provides the potential difference (voltage). The battery does not store electrical energy. It stores chemical energy that is converted to electrical energy as it discharges.
Generator
The Generator produces free electrons necessary to charge the battery. The electron flow is produced through inductance, a magnetized rotor spinning inside a stator. The generator produces AC voltage which is converted to DC voltage or rectified.
Generator styles
- Brush Type.
- Brushless Type.
Note. In an attempt to standardize terminology in the industry, the term alternator is being replaced with generator. Often an alternator is referred to as an AC generator.
Air or liquid (coolant) is used for generator cooling.
Brush Type Generators
Brush Type generators consist of the following main components
- Generator Housing.
- Stator Assembly.
- Rotor Assembly.
Generator Housing
The Housing is made of two pieces of die-cast aluminum. Aluminum is used because it is nonmagnetic, light weight and provides good heat dissipation.
Bearings for support of the rotor assembly are mounted in the front and rear housings.
Scheme 81
Brushless Type Generators
Brushless Type generators are liquid cooled (coolant) and consist of the following main components
- Generator Housing.
- Stator Assembly.
- Rotor Assembly.
Scheme 82
Generator Housing Water Cooled
The Water Cooled Generator is housed in an encapsulated metal shell enclosure. The enclosure is installed an aluminum shell.
The space between the inner surface of the shell and the outer surface of the generator creates a water jacket that engine coolant flows through.
Coolant flows from the engine into the shell through internal ports and exits via hose connections.
Liquid cooling minimizes noise generation through elimination of generator cooling fan.
Drive Belt
It is the function of the Drive Belt to transfer rotating energy from the engine to the generator. The drive belt rotates the rotor, spinning the magnetic field. A loose belt can inhibit charging system efficiency and a belt that too tight causes early bearing failure.
Voltage Regulator
Voltage Regulators prevent excessively high voltage output of the generator. Excessive voltage would cause damage to the battery (through overcharging), light bulbs, motors, and particularly sensitive electronic components.
The regulator prevents these problems by limiting the current output of the generator.
Two types of regulators that are used
- Standard Regulator.
- Multifunction Controller.
Standard Regulator
Electronic Voltage Regulators are mounted internally in the back of the generator assembly. Generator output is controlled by varying the amount of time the field coil is energized. The duty cycle of the field coil ground side is varied based on the demand placed on the electrical system.
The electronic voltage regulator compares field current supply voltage (from the stator windings through the diode trio) against a set voltage level ( using a zener diode).
As the field current supply voltage surpasses the zener diode's breakdown voltage, the field current to the rotor is switched off. When the field current voltage to the rotor is off, the generator is not producing voltage. A rapid switching of the field current allows a fixed voltage output to be maintained. Additional diodes in the regulator, prevent current flow when the ignition is off preventing battery drain.
Multifunction Controller
In addition to voltage regulation, the Muti-function Control electronic regulator provides the following features
- Load response during start-up.
- Load response during driving.
- Fault display (under voltage, drive belt breakage, field coil interruption).
Note. Multi-function Control electronic regulators are available with and without start load response. The only difference is the time limitation of the rated current during the start procedure.
The start-up load response system provides for the alternator exciter current (field coil) to be started by a transistor two seconds after the battery indicator goes out. This means that engine start-up is unaffected by generator induced drag.
The load response during driving ensures that when large current consumers are switched on the generator output increases linearly allowing the DME/EML system to stabilize the engine speed and/or modify injection time if necessary.
Charge Indicator
The purpose of the Charge Indicator is to advise the driver that the vehicle's electrical system is not operating at peak efficiency and service should be performed.
The charge indicator operates differently depending on which type of regulator the vehicle is equipped with.
The charge indicator operates on the basis of opposing voltages. If there is no output through the diode trio, then the lamp circuit is completed to ground through the rotor field. Diode output applies voltage to the previously grounded side of the bulb, turning the bulb off (No current flow with equal voltage on both sides of the bulb).
The charge indicator is activated by an electronic switch integrated in the controller. This internal switch receives its voltage supply from KL15 of the 2 pin generator connector. The controller measures internally the difference in voltage between KL30 and KL15 and switches the indicator circuit low in case of a fault.
Ignition Switch
The Ignition Switch provides initial power for the field circuit of the alternator, reducing the time required for the field to develop the magnetic field. Depending on which type of regulator is employed the ignition switch supplies power to the charge indicator to check bulb integrity.
Voltage Rectification
The battery and the electrical system cannot store or use the 3-phase AC voltage produced by a generator, it must be rectified or converted to DC voltage.
A diode rectifier bridge is used to make the conversion.
The diode is similar to a non-return or one way valve which permits the passage of a fluid or gas in only one direction.
Scheme 83
In a simple conversion the rectifier diode suppresses the negative half waves and allows only positive half waves to pass.
To make use of the negative value half waves full rectification is applied.
Full rectification of the negative half waves invert them into positive half waves.
The result is a rectified pulsating direct current.
Scheme 84
Rectified Pulsating DC current
Three-Phase Voltage Regulation
Six diodes are used to achieve three-phase AC voltage rectification. Three diodes are positive biased and three are negative biased.
The positive half-waves pass through the positive biased diodes and the negative halfwaves through the negative biased diodes.
Diode rectification of the negative half-waves invert them into positive half-waves.
With full rectification DC voltage supplied to vehicle by generator is not ideally smooth, but exhibits a slight ripple. This ripple is further smoothed by the battery which is connected in parallel with the generator.
The rectifier diodes in the generator not only convert the current but also prevent battery discharging through the 3 phase windings of the stator. Current flow can only take place from the generator to the battery.
Scheme 85
Current flow through Y wound stator.
Scheme 86
Rectified AC output has a ripple as seen on oscilloscope.
Scheme 87
Current flow through Delta wound stator.
The Electronic Regulator uses a zener diode that blocks current flow until a specified voltage is obtained.
Sensing current from terminal 2 passes through a thermistor to the zener diode (D2). As the system voltage exceeds the breakdown voltage of the zener diode, current flows through the zener diode turning transistor 2 (TR2) on. With TR2 on transistor 1 (TR1) is shut off.
Scheme 88
Transistor 1 controls field current to the rotor. With TR1 off no current flows to the field coil and the generator has no output.
A voltage drop below the breakdown voltage of the zener diode stops the current flow to TR2 which turns on TR1.
Voltage is again applied to the field allowing the generator to produce voltage.
Scheme 89
Field coil off, no charging.
The Multifunction Controller regulates voltage in the same manner as the standard voltage regulator. Regulation is through duty cycle control of the field coil.
The differences as compared to the standard regulator are
- Manner in which malfunction indicator lamp is controlled.
- Connections to wiring harness.
Scheme 90
Terminal 1
KL 15 from fused source.
Terminal 2
D+ (KL61) to DME.
B+
Generator output to Battery.
Scheme 91
Two Pin wiring harness connector
Harness connector
B+ connection.
Scheme 92
The Charging System Indicator light operates on the principle of opposing voltage. Battery voltage is supplied to one side of the light bulb, the other side of the bulb is connected to the voltage regulator. With the key turned on, power is sent to the light bulb, through to the regulator. No voltage is being produced by the stator, so there is no voltage from the diode trio. This lack of voltage from the diode trio, allows the voltage from the ignition switch to flow through the regulator to ground. This completes the circuit allowing the charge indicator bulb to burn.
As the generator begins to produce voltage, the output of the diode trio equals battery voltage. This equal voltage is supplied to the light bulb. With equal voltage on each side of the light bulb, no current can flow and the light is turned off.
Scheme 93
The charge indicator light is activated by means of an electronic switch integrated into the controller. This switch receives its voltage supply from terminal 15 on the 2 or 3 pin connector on the generator. Terminal D+ is replaced by an isolated electronic terminal 61E in generators with a multifunction controller. The task on this terminal is to activate the battery charge indicator lamp and to indicate to the various loads that the generator is in charge mode.
The indicator lamp is supplied with voltage via terminal 15 from the instrument cluster. The lamp is illuminated when the voltage at terminal 61E is below 1.5v and goes out when the voltage is above 8v.
The indicator is on during the following conditions
- Key on, engine off.
- Generator not charging.
- Failure of drive belt.
- Interruption of field coil.
- Controller overvoltage.
- Break in charging cable.
