The charging system consists of an alternator containing a rectifier pack and regulator to maintain a constant direct current (dc) voltage in the system. The alternator is belt driven from the crankshaft and cooled by a fan mounted behind the pulley. The alternator has a fixed coil wound stator in which a field coil rotor rotates. Slip rings conduct current to and from the field coils via 2 carbon brushes. The regulator senses output voltage and controls this to approximately 14 volts.
Charging
Feed from the positive battery terminal is connected to the engine compartment fuse box (C632-1) by a brown wire. Current passes through fusible link 2 and fusible link 3, which are connected in parallel. Fusible link 2 (C907-2) is connected to the ignition switch (C028-1) by a brown wire. With the ignition switch in position "II" (C094-1), a feed is supplied to the ignition/no charge warning lamp (C230-5) on a white wire.
The warning lamp (C230-5) is earthed via the diode (C118-1) on a yellow/brown wire and through the alternator field windings (C185-1) on a brown/yellow wire. The flow of current through the warning lamps and field windings partially magnetises the rotor. A resistor (C037-1 & C038-1) is wired in parallel with the warning lamps to ensure continued exciter voltage in the event of bulb failure.
When the engine starts, the magnetised rotor rotates within the stator windings, generating a 3 phase alternating current (ac) and voltage which rises rapidly with rotor speed. The field diodes convert the ac current to direct current (dc) and the generated voltage is fed back to the field windings. As the feed back voltage increases, the magnetic influence of the rotor also increases, resulting in self-excitation of the rotor. Generated current and voltage increases with rotor speed until the alternator is fully excited.
When the alternator outputs a voltage equal to that supplied by the battery, the warning lamp is extinguished as the potential difference across the lamp is 0 volts. The diode between the alternator and warning lamp prevents reverse flow.
The regulator functions as an electronic control switch on the earth side of the field coils. The regulator rapidly switches the earth circuit off and on to control the generated voltage and current to safe limits.
If the battery is in a low state of charge or current draw from the electrical system is high and causes a voltage drop, the alternator charges at its maximum rate until 14 volts is generated. As battery voltage rises, the generator current output reduces.
Starting
Feed from the positive battery terminal is connected to the engine compartment fuse box (C632-1) by a brown wire. Current passes through fusible link 2 and fusible link 3, which are connected in parallel. Fusible link 2 (C907-2) is connected to the ignition switch (C028-1) by a brown wire.
When the ignition switch is turned to the "crank" position, power flows across the switch (C090-1) to the starter relay coil (C151-85) on a white/red wire. Current then flows from the starter relay (C151-86) to the alarm ECU (C057-10) on a black/orange wire. Assuming the alarm ECU has received the correct code from the RF handset, it will complete the path to earth (C057-11) on a black wire and energize the starter relay.
Power from fusible link 2 (C907-2) can now flow across the starter relay switch and onto the engine immobilisation ECU (C863-6). Again, assuming the alarm ECU has received the correct code from the RF handset, it will inform the engine immobilisation ECU (C863-10) to provide a feed to the starter motor solenoid (C179-1) on a black wire. This feed will energize the solenoid, allowing a positive feed from the battery to flow across the solenoid (C178-1) and power the starter motor. An earth is provided by the starter motor.
Glow Plugs
Glowplugs are fitted to the Tdi engine to assist starting. A constant battery feed is supplied by fusible link 3 (C907-3) to the glow plug timer (C189-5) on a brown wire. When the ignition switch is turned to position "II", a second feed is supplied to the glow plug timer (C189-3). This triggers a feed (C189-6) to the glow plugs.
With the ignition switch in position "II", the glow plug warning lamp (C230-4) is provided a feed via fuse 17 (C580-33) of the passenger compartment fuse box on a white wire. The warning lamp (C233-10) is connected to the glow plug timer (C189-2) by a yellow/black wire.
When the glow plug timer provides a feed for the glow plugs (C189-6), it simultaneously provides an earth path (C189-4) for the warning lamp. After a set period, feed to the glow plugs, and the earth path for the warning lamp are cut; extinguishing the warning lamp.