Electrical and Electronic Systems
Batteries, alternators, starters, CAN bus, multiplexing, and diagnostic tools.
- Identify battery types and standard voltage systems for commercial trucks
- Describe alternator function and diagnose low charging voltage
- Explain starter motor operation and proper jump start procedures
- Describe CAN bus and multiplexed electrical systems
Lesson 1
Batteries and Charging Systems
Battery Fundamentals
The most common type of battery in trucks is the lead-acid battery. Commercial trucks use either 12 or 24 volt systems. Most North American Class 8 trucks use a 12-volt system with three or four Group 31 12V batteries wired in parallel - this keeps the system at 12V while combining Cold Cranking Amps (typically 3000-4000+ CCA total) needed for high-displacement diesel starting. 24-volt systems use two 12V batteries in series (voltage additive) and are the standard in European trucks, where reduced current draw allows thinner gauge wiring.
Alternator Function
The alternator charges the battery and powers electrical systems while the engine is running. It converts mechanical energy from the engine (via belt drive) into AC electrical energy, then rectifies it to DC for the vehicle electrical system. The voltage regulator (often built into the alternator) controls output voltage to prevent overcharging.
Low Charging Voltage
Low charging voltage is caused by worn brushes, faulty regulator, or loose belt. Other causes include high-resistance connections, a failing rectifier bridge, or excessive electrical loads that exceed the alternator's output capacity.
Charging System Test
Normal charging voltage is 13.5-14.5V (12V system) or 27-29V (24V system) at operating RPM. Voltage below this range indicates a charging problem. Always check belt tension and connections before replacing the alternator.
Trucks use lead-acid batteries in 12 or 24 volt configurations. The alternator charges the battery and powers electrical systems. Low charging voltage is caused by worn brushes, faulty regulator, or loose belt.