Lesson Notes By Weeks and Term v3 - Senior Secondary 1
Auxiliary circuit diagram
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Auxiliary circuit diagram
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Subject: Auto Electrical Works
Class: Senior Secondary 1
Term: 2nd Term
Week: 4
Theme: Auxiliary System
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Read and in terpretauxiliary circuitdiagram. Draw an auxiliarycircuit diagram. Label each unitthat is classified as auxiliary.
Auxiliary System Solution to Question 2: ``` +V (Battery Positive) | [FUSE] (e.g., 20A for brake lights) | [BRAKE PEDAL SWITCH] (Normally Open, closes when pedal pressed) | /----------[BRAKE LIGHT BULB 1]----------\ | | \----------[BRAKE LIGHT BULB 2]----------/ | [GROUND] | -V (Battery Negative) ``` Explanation: The circuit starts from the positive terminal of the battery. A fuse protects the entire brake light circuit. The Brake Pedal Switch is normally open (no current flow). When the brake pedal is pressed, the switch closes. When the switch closes, current flows to both Brake Light Bulbs (connected in parallel, so if one fails, the other can still work). From the bulbs, the current returns to the Ground (chassis) and back to the negative terminal of the battery. --- Question 3 (Labeling and Identification) Identify which of the following vehicle components are classified as auxiliary electrical units. For each identified auxiliary unit, state its primary function. a) Starter Motor b) Horn c) Fuel Injector d) Headlamp Assembly e) Power Window Motor f)
Alternator Solution to Question 3: The following components are classified as auxiliary electrical units: b)
Horn: Primary function is to provide an audible warning signal. d)
Headlamp Assembly: Primary function is to illuminate the road ahead for night driving and make the vehicle visible to others. e)
Power Window Motor: Primary function is to mechanically raise or lower the vehicle's windows.
Explanation of non-auxiliary units: a)
Starter Motor: Part of the primary starting system, essential for cranking the engine. c)
Fuel Injector: Part of the engine management system, essential for fuel delivery to the engine. f)
Alternator: Part of the charging system, essential for generating power and charging the battery while the engine is running.
5. Independent Practice (Questions Only)
1. Draw a complete circuit diagram for a vehicle's interior dome light that is controlled by a single ON/OFF toggle switch, including the battery, fuse, bulb, and ground. Label all components clearly.
2. Provide a step-by-step explanation of how to interpret a circuit diagram showing a car radio connected to the battery, an inline fuse, and a speaker.
3. List five (5) electrical components that are not typically classified as auxiliary in a car and briefly explain why.
4. Draw the standard automotive electrical symbols for: a) Battery b) Fuse c) Lamp (Bulb) d) Push-button Switch (Normally Open) e) Ground
5. A vehicle owner reports that their turn signals (indicators) are not working, but the hazard lights function correctly. Based on your understanding of auxiliary circuits, suggest a likely fault area for the turn signals.
6. Explain the purpose of a fuse in any auxiliary circuit and describe what happens when a fuse "blows."
7. Consider a circuit with a battery, a fuse, a switch, a relay (coil and contacts), and a high-current load (e.g., powerful off-road lights). Explain why a relay is used in such a circuit instead of directly wiring the switch to the load.
8. Identify three (3) advantages of understanding auxiliary circuit diagrams for a roadside mechanic in a typical Nigerian setting.
6. Evaluation and Assessment 6.
1. Formative Assessment Question and Answer Session: Throughout the lesson, the teacher should ask targeted questions to check for understanding of symbols, component functions, and circuit flow.
Observation of Practical Work: Observe students' attempts during guided practice for drawing and interpreting diagrams, providing immediate feedback.
Quick Quizzes: Administer short quizzes on symbol identification or tracing simple circuit paths. 6.
2. Summative Assessment Assessment Question 1 (Reading and Explaining Auxiliary Circuit Diagram) Observe the provided simplified circuit diagram for a vehicle's reverse light system. ``` +V (Battery Positive) | [FUSE - R/L (Reverse Light)] | [IGNITION SWITCH] (ACC/ON position) | [REVERSE SWITCH] (Normally Open, closes when reverse gear engaged) | /----------[REVERSE LIGHT BULB 1]----------\ | | \----------[REVERSE LIGHT BULB 2]----------/ | [GROUND] ``` Explain, in detail, the operational sequence of this reverse light circuit from the moment the engine is started and the driver selects the reverse gear. Clearly state the role of each component in the circuit.
Marking Scheme for Assessment Question 1: * Identification of Power Source and Fuse: 1 mark Auxiliary circuit diagram Term: 2nd Term Week: 17 ---
1. Overview and Learning Objectives This topic introduces students to auxiliary electrical circuits in automobiles. While primary circuits are essential for engine operation, auxiliary circuits enhance a vehicle's safety, convenience, and comfort. Understanding these circuits is fundamental for diagnosing electrical faults, performing maintenance, and installing aftermarket accessories, skills highly relevant to the automotive industry in Nigeria. This knowledge equips future technicians and enthusiasts with practical skills applicable to a wide range of vehicles, from commercial buses (`danfo`, `molue`) to private cars, commonly found on Nigerian roads. Upon completion of this lesson, students will be able to: Understand and explain the symbols, connections, and operational principles depicted in an auxiliary circuit diagram. Create a basic drawing of an auxiliary circuit diagram, correctly illustrating the power source, protective devices, switches, loads, and grounding points. Accurately name and identify various electrical components that are classified as auxiliary within a vehicle's electrical system. These objectives are crucial for real-world applications such as: Troubleshooting common electrical problems like faulty headlights, non-functional horns, or inoperative windscreen wipers, which are critical for vehicle roadworthiness and safety in Nigeria. Properly installing or repairing accessories such as car radios, charging ports for mobile devices in commercial vehicles, or additional lighting, ensuring functionality and preventing electrical damage. Understanding the electrical layout of vehicles for efficient maintenance and repairs, contributing to safer transportation and more reliable vehicles across the country.
2. Key Concepts and Explanations 2.
1. Definition of Auxiliary Circuit Auxiliary circuits are electrical systems within an automobile that are not directly involved in the engine's primary operation (ignition, fuel injection, starting). Instead, they provide power for features that enhance driver and passenger safety, comfort, and convenience. These circuits typically draw power from the vehicle's battery and are protected by fuses or circuit breakers.
Examples of Auxiliary Systems: Lighting Systems: Headlights (low beam, high beam), tail lights, brake lights, turn signals (indicators), hazard lights, interior dome lights, dashboard illumination.
Warning Systems: Horn, seatbelt warning light, low fuel warning light.
Wiper and Washer Systems: Windscreen wipers, rear window wipers, washer pumps.
Convenience Systems: Power windows, central locking, car radio/infotainment system, cigarette lighter/12V power outlets, power seats (in some vehicles).
Security Systems: Car alarms, immobilizers. 2.
2. Basic Components of an Automotive Electrical Circuit All automotive electrical circuits, including auxiliary ones, consist of fundamental components: Power Source (Battery & Alternator): Battery: Stores chemical energy and converts it to electrical energy (DC) to power the vehicle's electrical components, especially when the engine is off or starting. Typically 12V in modern vehicles.
Alternator: Generates alternating current (AC) which is then rectified to direct current (DC) to charge the battery and supply power to the vehicle's electrical systems when the engine is running. Protection Devices (Fuses & Circuit Breakers): Fuse: A safety device containing a thin wire designed to melt and break an electrical circuit if the current exceeds a specified level. This protects the wiring and components from damage due to overcurrent or short circuits. Fuses are one-time use and must be replaced after blowing.
Circuit Breaker: An automatic electrical switch designed to protect an electrical circuit from damage caused by overcurrent or overload. Unlike a fuse, it can be reset (manually or automatically) to resume normal operation. Common in systems with high current draws or where temporary overloads might occur.
Switches: Devices that open or close an electrical circuit, thereby controlling the flow of current to a component.
Manual Switches: Operated by the driver (e.g., headlight switch, wiper switch, horn button).
Automatic Switches (Relays): Electrically operated switches that allow a small current in a control circuit to switch a larger current in a power circuit. This protects sensitive switches and allows for shorter, heavier gauge wiring for high-current loads.
Sensor-activated Switches: Activated by environmental conditions (e.g., door switch for interior light).
Conductors (Wires): Typically copper wires, insulated with plastic, that provide the path for electrical current to flow between components. Different wire gauges (thickness) are used depending on the current capacity required. * Loads: The electrical wiper switch, horn button).
Automatic Switches (Relays): Electrically operated switches that allow a small current in a control circuit to switch a larger current in a power circuit. This protects sensitive switches and allows for shorter, heavier gauge wiring for high-current loads.
Sensor-activated Switches: Activated by environmental conditions (e.g., door switch for interior light).
Conductors (Wires): Typically copper wires, insulated with plastic, that provide the path for electrical current to flow between components. Different wire gauges (thickness) are used depending on the current capacity required.
Loads: The electrical components that consume electrical energy to perform work (e.g., light bulbs produce light, motors produce motion, horns produce sound, radios produce sound).
Ground: The return path for electrical current to the negative terminal of the battery. In vehicles, the chassis and body often serve as the common ground connection, reducing the amount of wiring needed. 2.
3. Reading and Interpreting Auxiliary Circuit Diagrams Circuit diagrams use standardized symbols to represent components and lines to represent wires.
To read a diagram:
1. Identify the Power Source: Usually the battery (indicated by symbols resembling positive and negative plates). The positive terminal is often marked with a `+` and the negative with a `-` or connected to ground.
2. Locate Protection Devices: Fuses or circuit breakers are typically found immediately after the power source on the positive side, protecting the entire circuit or specific branches.
3. Follow the Current Path: Conventionally, current flows from the positive terminal of the battery, through the protection device, to a switch.
4. Identify Switches: Observe the type of switch (e.g., push-button, toggle, multi-position, relay). The switch's position (open or closed) determines if current flows.
5. Identify Loads: After the switch, the current flows to the load (e.g., a bulb, motor, horn). The load converts electrical energy into another form (light, motion, sound).
6. Locate Ground: From the load, the current returns to the negative terminal of the battery, usually via a ground point on the chassis. The ground symbol (three decreasing parallel lines or an inverted triangle) indicates this connection.
7. Trace Parallel Branches: Many auxiliary circuits have multiple components connected in parallel. Each branch will have its own path to the load and then to ground.
Common Automotive Electrical Symbols: Battery: `[+ ||| -]` (rectangular cells) or `[+ () -]` (circle with + and -)
Fuse: `---[~]---` (zigzag line between two dots) or `---[| |]---` (rectangle with a line in the middle) Switch (SPST - Single Pole, Single Throw): `---/ -----` (line with a break and a diagonal line/lever)
Lamp/Bulb: `---O---` (circle with a cross inside)
Motor: `---M---` (circle with 'M' inside)
Horn: `---( ))---` (circle with sound waves emanating)
Resistor: `---/\/\/\---` (zigzag line)
Relay (Coil): `---( )---` (rectangle or coil shape)
Ground: Three decreasing parallel lines `_ _ _` Wire Junction: A dot `.` where lines cross/meet Wire Crossing (no connection): `---` (line passing over another without a dot) Worked Example (Reading a Simple Headlamp Circuit): Consider a basic circuit for a single low-beam headlamp. ``` +V (Battery Positive) | [FUSE] (e.g., 15A) | [HEADLIGHT SWITCH] (ON/OFF) | [HEADLAMP BULB] | [GROUND] ``` Explanation:
1. Current flows from the Battery Positive (+V) terminal.
2. It passes through the FUSE, which protects the circuit from excessive current. If the fuse blows, the circuit opens, and the headlamp will not light.
3. The current then reaches the HEADLIGHT SWITCH. When the switch is in the "ON" position, it closes the circuit.
4. Current flows from the switch to the HEADLAMP BULB, causing it to illuminate.
5. Finally, the current leaves the bulb and returns to the GROUND (vehicle chassis), which is connected to the Battery Negative terminal. 2.
4. Drawing an Auxiliary Circuit Diagram To draw an auxiliary circuit diagram, follow these steps:
1. Identify Components: List all the components required for the specific auxiliary system (e.g., for a horn: battery, fuse, horn button, horn unit, wires).
2. Place Power Source: Draw the battery symbol on one side, typically the top or left, indicating the positive and negative terminals.
3. Add Protection: Draw the fuse symbol immediately