Understanding Automotive Electrical Systems: Key Concepts and Components
Vi: Instantaneous Tension
Vi represents the tension at a specific instant in time over a given angle.
Vp: Maximum Coil Tension
Vp is the maximum tension generated by the coil.
Counter-Electromotive Force
When the engine is spinning, it acts as a power generator, producing a counter-electromotive force that opposes the applied voltage.
Vblokeo: Starter Block Voltage
Vblokeo is the voltage measured at the battery terminals when the starter is blocked.
F: Frequency
F is the number of cycles performed in one second.
T: Period
T is the time it takes to complete one cycle.
Saturation
Saturation occurs when dipoles are oriented and cannot support more lines of force.
Hysteresis
Hysteresis is the delay between magnetization and the force field.
Starter Motor Operation
Current enters the inductor coil through brushes and the armature of these spools with a large section. This generates a stationary magnetic field. The contactor circuit cuts the starter battery to a few contacts and is composed of two coils and a mobile core that moves through the inside. When it moves, the contacts come together and close the circuit, feeding the starter.
Alternator Excitation Current Connected
While the alternator voltage is below the breakdown voltage of the Zener diode, current does not pass to transistor T1. Current passes through excitation diodes from B+ through R6, connecting transistor T2 and terminal T3 (DF). Now, T2 and T3 are the drivers, passing through the excitation coil. The intensity increases, raising the input voltage of the Zener diode.
Alternator Excitation Current Switched Off
Now, the voltage is from D+ through R1, R2, and the diode. When transistor T1 becomes the driver, the voltage of T2 decreases, closing T2 and T3. The voltage drops back due to inductance in the excitation, deviating to D3 in parallel with the excitation voltage, reconnecting the excitation.
Alternator Self-Excitation Circuit
This occurs when the alternator produces at least 1.4V per phase. The pre-excitation current flows from the positive terminal of the alternator to the positive battery terminal through the control lamp. While the lamp is on, the alternator is not producing usable current. When the rotor reaches sufficient speed, the lamp turns off, and the alternator begins supplying self-excitation current to the vehicle.
Excitation Circuit
Once self-excited, the alternator rotor creates a magnetic field strong enough to induce alternating current in the stator. Part of this current is rectified by auxiliary excitation diodes, reaching the regulator incorporated into the controller terminal. It is then excited, closing the circuit through the D- terminal and negative diodes. For unincorporated regulators, the current goes from the alternator’s D+ terminal to the regulator’s D+ terminal, carried by the excitation. The main part of the induced current is rectified by the power rectifier diode bridge, conducted through the B+ terminal from the alternator to the battery and services, returning through B-.
Residual Magnetism
Residual magnetism is the amount of magnetism a substance retains.
Detailed Starter Operation
When the ignition key is turned, current flows to the battery contactor’s coils, creating a magnetic field. This moves the core, advancing the pinion to engage the flywheel. The main contacts close, sending current from the battery in series with the excitation. However, the gear teeth compress the spring, rotating the pinion and closing the motor contactor. The pinion begins to rotate the freewheel. When the engine starts, the freewheel unlocks. Turning off the ignition key returns the core to its position, opening the contacts and cutting off the motor current. The pinion disengages due to the fork’s movement.