Ignition & Electrical Systems
Battery testing, charging system, starter circuits, ignition coils, spark plugs, relays, fuses, circuit protection, and voltage drop testing.
- State the typical voltage of a fully charged battery and charging system output
- Explain alternator operation, rectifier function, and voltage regulation
- Describe ignition coil testing and spark plug wire resistance specifications
- Identify the purpose of fuses, relays, and circuit breakers
- Perform voltage drop testing to diagnose electrical circuit problems
Leçon 1
Battery Testing, Starter Solenoid & Starting Circuit
The Automotive Battery
The battery is the foundation of the entire electrical system. It provides power for starting, stabilizes voltage during operation, and powers accessories when the engine is off.
The typical voltage of a fully charged automotive battery is 12.6 volts. This is measured with the engine off and no loads on the battery. A reading below 12.4 volts indicates the battery needs charging; below 12.0 volts indicates a significantly discharged battery.
The Starter Solenoid
The starter solenoid functions to engage the starter motor and connect battery power. When you turn the key or press the start button, a small current flows through the solenoid coil, which pulls a plunger that does two things simultaneously: pushes the starter drive gear into the flywheel ring gear and closes a heavy-duty contact that sends full battery current to the starter motor.
Parasitic Battery Drain Testing
The proper method for testing parasitic battery drain is to use an ammeter in series with the battery to measure current draw. Normal parasitic draw with the vehicle off should be below 50 milliamps. Higher draw indicates a module not going to sleep or a circuit staying energized when it should be off.
A fully charged battery reads 12.6 volts. The starter solenoid engages the starter and connects battery power. Test parasitic drain with an ammeter in series - normal draw is below 50mA.