# Unit 47:

### Unit introduction

In this unit, learners will gain an understanding of electrical and electronic principles through the analysis of direct current (DC) motor vehicle electrical circuits. Learners will be introduced to the principles and properties of magnetism as applied to motor vehicle circuit devices.

Learners will examine the concepts of digital electronic principles and microprocessor applications in motor vehicles. They will be introduced to single-phase alternating current (AC) theory as applied to vehicle alternators.

They will consider waveform characteristics and determine the values (using phasor and algebraic representation and actual waveform measurements using an oscilloscope) of alternating quantities.

This unit has been designed to encourage learners to take an investigative approach through practical construction, measurement and testing of circuits and, where applicable, the use of computer-based circuit analysis and simulation.

Note that the use of ‘e.g.’ in the content is to give an indication and illustration of the breadth and depth of the area or topic. As such, not all content that follows an ‘e.g.’ needs to be taught or assessed.

### Learning outcomes

On completion of this unit a learner should:

• Be able to use circuit theory to determine voltage, current and resistance in direct current (DC) motor vehicle circuits
• Understand the principles, properties and applications of magnetism in motor vehicle technology
• Know the concepts of digital principles and applications of microprocessors in motor vehicles
• Be able to use single-phase alternating current (AC) theory to determine vehicle alternator

### Unit content

• Be able to use circuit theory to determine voltage, current and resistance in direct current (DC) motor vehicle circuits

DC circuit theory: voltage, e.g. potential difference, electromotive force (emf); resistance, e.g. conductors and insulators, resistivity, temperature coefficient, internal resistance of a DC source; circuit components (power source, e.g. battery, stabilised power supply; resistors, e.g. function, types, values, colour coding; diodes, e.g. types, characteristics, forward and reverse bias modes); circuit layout (DC power source, resistors in series, resistors in parallel, series and parallel combinations); Ohm’s law, power and energy formulae,

e.g. V = IR, P = IV, W = Pt; application of Kirchoff’s voltage and current laws

DC motor vehicle circuits: circuits to include a DC power source, four components including circuit protection and switching arrangement; vehicle applications, e.g. lighting circuits (side and rear lamp, main and dip headlamp, front and rear fog lamps, stop lamp, reverse lamp, indicator and hazard warning system), auxiliary circuits (horn, window winding, central locking, interior heater, rear screen heater), vehicle security systems, air-conditioning, use of relays, circuit protection devices (DC power source circuit protection fuse and resistors (series/parallel)), operating component(s) such as motor assembly; diode resistor circuit with DC power source, series resistors and diodes,

e.g. bulb failure circuit, low oil pressure circuits, alternator rectifier

Measurements in DC motor vehicle circuits: safe use of a multimeter,

e.g. setting, handling, health and safety; measurements (circuit current, voltage, resistance, internal resistance of a DC power source); testing a diode’s forward and reverse bias

• Understand the principles, properties and applications of magnetism in motor vehicle technology

Characteristics of magnetic field: field patterns (flux, flux density (B), magnetomotive force (mmf) and field strength (H), permeability, B/H curves and loops); ferromagnetic materials; reluctance; magnetic screening; hysteresis

Electromagnetic induction: principles, e.g. induced emf, eddy currents, self and mutual inductance; motor vehicle applications (electric motor/generator, e.g. series and shunt motor/generator, transformer, e.g. primary and secondary current and voltage ratios); motor vehicle applications of Faraday and Lenz’s laws, e.g. electrical induction in an alternator, electromagnetic coil

• Know the concepts of digital principles and applications of microprocessors in motor vehicles

Digital principles: binary system, e.g. binary notation and algebra, bits and bytes, input/output (I/O) voltage levels; logic system, e.g. AND, OR, NOT NAND and NOR gates; truth tables, memory circuits, sequential and clocked circuits, flip flops, read-only memory (ROM)/random-access memory (RAM) structures and organisation; timers; digital to analogue (D/A) and analogue to digital (A/D) converters; types of integrated circuits, e.g. classification, operation, performance characteristics and identification; vehicle applications, e.g. fault diagnosis, code readers, data logging, visual/audio output, speed sensor processing, engine timing control, satellite navigation

Microprocessors: microprocessor system e.g. programmes, language, I/O interface, memory; construction of microprocessor, e.g. control section, arithmetic and logic sections, register section, memory, I/O section buses, fetch and execute cycle, control by clock pulses; motor vehicle application of microprocessors, e.g. engine management, anti-lock braking systems (ABS), climate control, suspension settings, transmission modes

• Be able to use single-phase alternating current (AC) theory to determine vehicle alternator performance

Single-phase AC circuit theory: waveform characteristics, e.g. sinusoidal and non-sinusoidal waveforms, amplitude, period time, frequency, instantaneous, peak/peak-to-peak, root mean square (rms), average values, form factor; determination of values using phasor and algebraic