Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Auxillary Circuit
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Auxillary Circuit
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Subject: Auto Mechanical Works
Class: Senior Secondary 2
Term: 2nd Term
Week: 3
Theme: Electrical System
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Identify maincomponents of eachauxiliary circuit. State the irfunctions Read and interprete variousauxiliary circuits.
Electrical System Auxiliary Circuit Term: 2nd Term Week: 18 ---
1. Overview and Learning Objectives This topic introduces teachers to the fundamental concepts of auxiliary circuits in automotive systems. Auxiliary circuits refer to the electrical systems in a vehicle that are not directly involved in the engine's operation or the primary charging/starting functions but are crucial for driver comfort, safety, and convenience. Understanding these circuits is vital for students pursuing careers as auto mechanics, technicians, or even general vehicle maintenance. It equips them with the knowledge to diagnose and repair common electrical faults, a skill highly valued in the Nigerian automotive industry. This knowledge is also critical for vehicle owners and inspectors to ensure roadworthiness and safety, particularly during pre-purchase inspections or annual vehicle checks prevalent in Nigeria. Upon completion of this lesson, students will be able to: Identify the main components of various auxiliary circuits (e.g., lighting, horn, wipers, power windows). Explain the function of each component within these circuits. Read and interpret basic auxiliary circuit diagrams. These objectives connect directly to real-world applications in Nigeria by enabling students to: Troubleshoot common vehicle electrical issues such as faulty headlights during night driving, non-functional wipers during heavy downpours, or malfunctioning car horns. Perform basic electrical repairs on vehicles, contributing to their entrepreneurial skills as auto-electricians. Understand the electrical systems relevant for vehicle pre-purchase inspection or ensuring personal vehicle safety and roadworthiness.
2. Key Concepts and Explanations Definition of Auxiliary Circuit: Auxiliary circuits are electrical systems in a vehicle designed to enhance comfort, safety, and convenience. They operate independently of the primary engine management, starting, and charging systems, though they all draw power from the main vehicle battery. Examples include lighting systems, horn, wipers, power windows, central locking, and infotainment systems.
Distinction from Main Circuits: Main Circuits: Directly involved in vehicle operation (e.g., Ignition system, Starting system, Charging system, Engine Management System - EMS).
Auxiliary Circuits: Enhance driver/passenger experience and safety, but the vehicle can technically move without them (e.g., Headlights, Wipers, Horn, Radio). General Circuit Components (Applicable to Auxiliary Circuits): All electrical circuits, including auxiliary ones, typically comprise:
1. Power Source: The vehicle battery (usually 12V in cars, 24V in some heavy-duty vehicles like trucks and buses commonly seen in Nigeria) provides the electrical energy.
2. Protection Devices: Fuses: Deliberately weak links in a circuit designed to melt and open the circuit if current exceeds a safe level, protecting components from damage due due to overcurrent or short circuits. Common types include blade fuses (mini, ATM, maxi), cartridge fuses, and glass tube fuses.
Circuit Breakers: Reusable electrical safety devices that automatically trip (open the circuit) when an overcurrent is detected and can be reset manually or automatically.
3. Switches: Devices used to open or close a circuit, controlling the flow of current to a component.
Manual Switches: Operated by the driver (e.g., headlight switch, horn button, wiper switch).
Automatic Switches: Activated by specific conditions (e.g., brake light switch activated by pedal, relay coils).
4. Loads: The components that consume electrical energy to perform a function.
Bulbs: Convert electrical energy into light (e.g., headlights, interior lights).
Motors: Convert electrical energy into mechanical motion (e.g., wiper motor, power window motor).
Solenoids: Electromagnets used to perform mechanical work (e.g., door lock actuators, starter solenoid).
Heating Elements: Convert electrical energy into heat (e.g., rear defogger).
5. Conductors: Wires and cables that provide pathways for current flow. They must be appropriately sized for the current they carry to prevent overheating.
6. Control Devices (Relays): Relay: An electromagnetic switch. It uses a small current in its control circuit (coil) to open or close a switch in a larger power circuit (contacts). This allows low-current switches to safely control high-current loads, protecting the primary switch from damage.
Types: Normally Open (NO) and Normally Closed (NC). An NO relay closes its contacts when energized; an NC relay opens its contacts when energized. Specific Auxiliary Circuits and Their Components/Functions:
A. Lighting System: Purpose: Provide illumination for driving, signal vehicle intent, and illuminate the interior.
Components: Battery: Power source.
Fuses: Protect lighting Mechanical assembly that guides the window glass. Function
Example: When a power window switch is pressed (e.g., "down"), it sends current to the window motor in a specific direction (e.g., forward), causing the motor to rotate and lower the window. Pressing "up" reverses the current direction (e.g., backward), raising the window.
Reading and Interpreting Circuit Diagrams: Circuit diagrams are schematic representations of electrical circuits using standard symbols.
Standard Symbols: Battery: (+ and - terminals)
Fuse: (Zigzag line with a box or simply a box)
Switch: (Break in line with an arm, indicating open/closed)
Lamp/Bulb: (Circle with a cross, or half-circle radiating lines)
Motor: (Circle with 'M' inside)
Resistor: (Zigzag line)
Ground: (Stacked parallel lines or inverted triangle)
Relay: (Coil represented by a rectangle or zig-zag line, contacts shown as switches) Tracing Current Flow (Worked Example - Simple Headlight Circuit): Objective: Trace the current path when the high beams are activated.
Assumed Components: Battery, Main Fuse, Headlight Switch (with High/Low Beam positions), High Beam Relay, High Beam Bulb, Ground.
1. Start at the Battery (+) terminal: Current leaves the battery.
2. Pass through the Main Fuse: Protection for the entire lighting system.
3. To the Headlight Switch: The switch is manually moved to the "high beam" position.
4. Through the Headlight Switch to the Relay Coil: This sends a small current to energize the coil of the high beam relay.
5. Relay Coil to Ground: Completes the control circuit, energizing the relay coil.
6. Relay Contacts Close: The energized relay coil pulls its internal switch (contacts) closed.
7. Current to Load via Relay Contacts: Now, a larger current flows directly from the Battery (+) (often via another fuse for the load side) → through the now-closed relay contacts → to the High Beam Bulb.
8. Bulb to Ground: The current passes through the bulb filament, causing it to light up, and then returns to the battery via the vehicle's chassis (ground).
Interpretation: This shows how a small current via the switch controls a larger current to the bulb through the relay, protecting the switch. If the fuse blows, no current flows. If the relay fails, the bulb won't light even with the switch on.
3. Teaching and Learning Activities Teacher Activities:
1. Introduction (10 minutes): Begin by asking students to brainstorm various electrical functions in a car beyond starting the engine (e.g., "What electrical things make a car comfortable or safe to drive?"). Write their answers on the board. Introduce the term "Auxiliary Circuit" and differentiate it from main circuits. State the lesson's objectives clearly.
2. Key Concept Explanation (25 minutes): Using visual aids (charts, projector, actual components if available), explain the general components of any auxiliary circuit: battery, fuses, switches, loads, conductors, and relays. Emphasize the role of fuses in protection and relays in current amplification/switch protection. Show examples of different fuse types commonly found in Nigerian vehicles (blade, cartridge). Systematically explain each major auxiliary circuit: Lighting, Horn, Wiper/Washer, Power Window.
For each: State its purpose. List and show (on chart/diagram/real component) its main components. Explain the function of each component.
3. Circuit Diagram Interpretation (20 minutes): Introduce standard circuit symbols. Draw them clearly on the board. Present a simplified circuit diagram (e.g., a horn circuit or a single headlight circuit) on a chart or projector. Demonstrate step-by-step how to trace current flow, identify components, and understand the circuit's operation. Emphasize the role of grounding in completing the circuit.
4. Guided Practical Activity (30 minutes): Group Activity: Divide students into small groups. Provide each group with a different simplified auxiliary circuit diagram (e.g., brake light, turn signal, interior dome light).
Task: Each group must identify all components, describe their functions, and trace the path of current flow in their assigned circuit. Circulate among groups, providing guidance and answering questions.
5. Wrap-up and Q&A (5 minutes): Review the main points of the lesson. Address any lingering questions from students.
Student Activities:
1. Participate in brainstorming and class discussions.
2. Observe and to draw a simple circuit diagram for a specific auxiliary system (e.g., a car horn circuit), correctly labeling all components and indicating current flow.
7. Real-life Applications / Integration
1. Automotive Repair and Troubleshooting (Entrepreneurship): Knowledge of auxiliary circuits is foundational for aspiring auto-electricians and mechanics in Nigeria. Common vehicle problems encountered daily, such as non-functional headlights, wipers that stop working during the rainy season, a horn that refuses to sound, or faulty power windows, all stem from issues within auxiliary circuits. Students who master this topic can competently diagnose these faults (e.g., a blown fuse, a faulty relay, a damaged switch) and perform necessary repairs, leading to viable self-employment opportunities or employment in workshops across the country.
2. Vehicle Roadworthiness and Safety (Community & Environment): Understanding auxiliary circuits is crucial for ensuring vehicle safety and compliance with road regulations in Nigeria. Functional brake lights, turn signals, headlights, and horns are mandatory for roadworthiness. For example, a vehicle with faulty brake lights poses a significant danger on busy Nigerian roads, especially at night or during heavy traffic. This knowledge helps vehicle owners perform basic checks and maintenance, and it's essential for vehicle inspectors who assess a car's fitness for the road, contributing to safer driving conditions and reducing accidents.
3. Vehicle Customization and Aftermarket Installations (Economy): Many vehicle owners in Nigeria customize their cars with aftermarket accessories like additional security systems, upgraded sound systems, fog lights, or reverse sensors. A solid understanding of auxiliary circuits allows students to safely and correctly integrate these accessories into a vehicle's existing electrical system without causing damage or creating fire hazards. This skill can open up specialized services in the automotive accessories market, catering to a growing demand.
8. Differentiation, Remediation and Extension Differentiation (for Struggling Learners): Simplified Visuals: Provide oversized, color-coded diagrams of auxiliary circuits with labels for each component. Use physical components (fuses, relays, bulbs, switches) for hands-on identification before introducing diagrams.
Paired Learning: Pair struggling learners with more advanced peers for guided diagram tracing and component identification.
Focus on Core Concepts: Prioritize the identification of the main components (battery, fuse, switch, load, ground) and their most basic functions, rather than complex circuit interactions.
Repetitive Practice: Offer flashcards with circuit symbols and component names/functions for repetitive review. Remediation (for Learners Needing Extra Support): Review Basic Electricity: Conduct a brief review of fundamental electrical concepts like current, voltage, resistance, open/closed circuits, and short circuits, as misunderstanding here can hinder progress.
One-on-One/Small Group Tutoring: Provide focused attention to re-explain concepts and walk through circuit tracing step-by-step.
Interactive Simulations (if available): Use online automotive electrical simulators or interactive diagrams that allow learners to "build" and test simple circuits, seeing immediate feedback.
Practical Deconstruction: If a discarded vehicle or wiring harness is available, guide learners to physically trace wires, identify components, and understand how they are connected in a real-world context.
Extension (for High-Achieving Learners): Advanced Circuit Design: Challenge learners to design a simple auxiliary circuit that performs a specific function (e.g., an automatic interior light that turns on when a door opens and fades out after a delay, or a simple car alarm circuit).
Troubleshooting Scenarios: Present them with more complex fault scenarios (e.g., "The left headlight works, but the right one doesn't. What are potential causes?") and ask them to develop a logical troubleshooting process.
Research Modern Systems: Encourage research into more advanced auxiliary systems found in modern vehicles (e.g., how the CAN bus system controls multiple auxiliary functions, smart wipers with rain sensors, or complex central locking systems). They can then present their findings to the class.
Component Dissection: Allow them to carefully disassemble non-functional components like relays or switches to understand their internal working mechanisms.