Electrical Principles

Electrical fundamentals	Basic electricity	Metals typically have many free electrons, and are good conductors. In insulators, electrons cannot easily move freely, so they are not readily available for electric current.
	Free electrons	For electric current to flow, the electrons need a complete pathway, or circuit. To make them move, there must be a force. It is called electromotive force, also known as voltage.
	Basic electronic principles	An n-type semiconductor has an excess of electrons. N for negative. If holes are in excess, it is a p-type. P for positive.
	Semi-conductors	Most electronic components combine p-type and n-type semi-conductors. Where they join is called the p-n junction. In this area, some electrons and holes cancel each other out. A thin layer forms, that acts like an insulator.
	Semiconductor device	Semiconductor devices are electronic components that exploit the electronic properties of semiconductor materials.
	Depletion layer	An insulating region within a conductive, doped semiconductor material where the charge carriers have been swept away through recombination.
	Dielectric	A dielectric, or electrical insulator, is a substance that is highly resistant to flow of electric current.
	Resistance	A measure of the degree to which an object opposes the passage of an electric current.
	Ground	Ground is a term used to indicate connecting a component to the vehicle frame or chassis.
	Ohm's law calculations	Using the rules of Ohm's Law gives an accurate method of determining values in an electrical circuit.
	Power equation	Electrical power is a measurement of output, or the rate of work. Unlike EMF, current flow and resistance, electrical power is not a direct measurement.

Sources of electricity	Electrostatic energy	Static electricity can be induced by rubbing two insulators together.
	Thermo-electric energy	Thermo-electric energy can produce electrical energy from heat energy.
	Electrochemical energy	Producing electrical energy from chemical energy is known as electrochemical energy. Most car batteries operate in this way.
	Photo-voltaic energy	Producing electrical energy from light energy is known as photo-voltaic energy.
	Piezo-electric energy	Producing electrical energy from mechanical stress is known as piezo-electric energy.
	Electromagnetic induction	When a conductor cuts across a magnetic field, current flows in the conductor.
	Electromagnetic components	When an electrical current passes through a wire, a small magnetic field is produced around the wire.
	Solar cells	A solar cell, or photovoltaic cell, is a semiconductor device consisting of a large-area p-n junction diode, which, in the presence of sunlight is capable of generating usable electrical energy.

Effects of electricity	Heating effects	Electricity can be transformed into other forms of energy such as the heat in head lamp bulbs.
	Chemical effects	Electricity may be used to store energy through chemical reactions such as in a lead acid battery.
	Magnetic effects	Sending current through coils on a shaft, in a magnetic field, draws them across the field. If the current is accurately switched, this attraction is constantly repeated to produce the rotary motion of the electric motor.
	Electrical conduction	The movement of electrically charged particles through matter.
	Electrical resistance	A measure of the degree to which an object opposes the passage of an electric current.
	Electromagnetic field	An electromagnetic field is considered to be limited to a local area around an object in space.

Circuits & measurement	Ohm's law	Ohm’s Law states that current flow in a circuit varies in direct proportion to changes in voltage, and in inverse proportion to the changes in resistance.
	Electrical power	In an electrical circuit, the unit of power is the watt. 1 watt is produced when 1 volt causes a current flow of 1 ampere.
	Watt	It is the rate in joules per second at which energy is being converted, used, or dissipated.
	Electrical measurement	An ammeter is connected in series. A voltmeter is connected in parallel. With an ohmmeter, the item to be tested must first be disconnected from its circuit.
	Series circuits	In a series circuit, the same current flows through every point of the circuit, but the voltage at different points can change.
	Parallel circuits	In a parallel circuit, all components are connected directly to the voltage supply. If one of the connections or components fails in a parallel circuit, current continues to flow through the rest.
	Parallel circuit resistance	Total resistance in a parallel circuit is found by adding the reciprocals of each resistance, then turning the answer back up the way it was.
	Series-parallel circuits	Series-parallel circuits are analyzed using the laws applied to separate series or parallel circuits.
	Wire sizing	Wire size is very important for the correct operation of electrical circuits. Selecting too small a gauge wire for an application will adversely effect the operation of the circuit. Selecting too large a gauge increases costs and weight.
	Networking & multiplexing	A multiplex network reduces the number of wires in the wiring harness and greater vehicle content flexibility.
	Fiber optics	Fiber optics are long, thin strands of very pure glass about the diameter of a human hair. They can be arranged in bundles and are called optical cables. Light signals can be transmitted along the cable over very long distances.

Wires & connectors procedures	Stripping wire insulation	When electrical wire is joined to other wires or connected to a terminal, the insulation needs to be removed.
	Installing a solderless terminal	Solderless terminals require a clean, tight connection. So make sure the wire and the connection are clean before fitting any terminals.
	Soldering wires & connectors	Flux is needed to prevent the metals being joined from oxidizing when they are heated.

Electrical testing procedures	Using a non-powered test light	Non-powered test lamps are very useful to determine a live part of a circuit.
	Using a lead light	Also known as drop lights or utility lights, the light they produce can make locating components and faults easier and more accurate.
	Using a DVOM to measure continuity	When checking continuity with a DVOM, the power supplied to the circuit during operation MUST be switched OFF.
	Using a DVOM to measure voltage	Always follow the specific manufacturer's instructions in the use of the meter, or serious damage either to the meter and/or to the electrical circuit could result.

Electrical components	Capacitors	Inside a capacitor are 2 surfaces, separated by insulating material. When the capacitor is charged, one surface is positively charged, the other is negative.
	Conductors & insulators	Conductors are materials that allow electrical current to flow. Insulators are materials that do not allow electrical current to flow.
	Wires	Electric wires are used to conduct electric current around the motor vehicle.
	Shielding	To prevent noise (interference), some vehicles use shielded wiring harnesses.
	Wire sizes	There are two scales used to measure the sizes of wires: Metric and AWG (American Wire Gauge).
	Length vs. resistance	Current capacity for different AWG wire sizes.
	Fuses & circuit breakers	Fuses and circuit breakers are used to protect electrical systems from allowing too much current to flow.
	Relays	Relays act as switches that are turned on and off by a small current. They can allow large current to be switched on and off in a circuit.
	Lamps	Turn electrical energy into heat energy and produce light. Various types of lamps are used in the automobile.
	Ballast resistor	A ballast resistor is used to reduce the voltage to the ignition coil during normal running conditions.

Electronic components	Diodes	In a circuit with an alternating current, a diode lets forward current through, but it blocks the reverse current. This is called rectifying the current.
	Types of diodes	The first diodes were vacuum tube devices (also known as thermionic valves), arrangements of electrodes surrounded by a vacuum within a glass envelope, similar in appearance to incandescent light bulbs.
	Lamps	Turn electrical energy into heat energy and produce light. Various types of lamps are used in the automobile.
	Resistors	Resistors are used to cause a drop in voltage in circuits. They are used to control current flow.
	Resistor ratings	To identify its value, each resistor is marked with four or five colored bands. Each color represents a number value, so by reading the color values it is possible to identify its resistance value.
	Variable resistors	Some resistors found in the motor vehicle are variable. Variable resistors can have their value altered by movement of a slide or by temperature change.
	Thermistors	Thermistors are semi-conductor resistors. Their resistance changes according to their temperature and they are used to control many electrical items in the automobile.
	Transistors	The 2 types of transistor are npn and pnp. In each type, the centre region is always the base. The outer regions are the collector, and the emitter. Transistors are used as switches, and to amplify currents.
	Avalanche diodes	An avalanche diode is a silicon diode that is designed to break down and conduct at a specified reverse bias voltage.
	Transient voltage suppression diodes	A transient system is a short-lived oscillation in a system caused by a sudden change of voltage, current or load.
	Zener diodes	A Zener diode contains a heavily doped p-n junction allowing electrons to tunnel from the valence band of the p-type material to the conduction band of the n-type material.
	P-n junctions	A p-n junction is formed by combining N-type and P-type semiconductors together in very close contact.
	Superconductors	Superconductivity is caused by a force of attraction between certain conduction electrons arising from the exchange of phonons, which causes the conduction electrons to exhibit a superfluid phase composed of correlated pairs of electrons.
	Thyristor	The thyristor is a solid-state semiconductor device similar to a diode, with an extra terminal which is used to turn it on.

Batteries	Lead acid batteries	Lead-acid batteries are the most commonly used rechargeable batteries today. They also represent the oldest design with one of the worst energy-to-wight ratios, they are cheap and can supply the high surge currents needed in started motors.
	Batteries & cells	Increasing the surface area of the plates in a cell increases its current capacity, but not its nominal voltage. Cells connected in series make a battery. The number of cells determines its nominal voltage.
	Battery charging	During discharge, the chemical energy of the plates is transformed into electrical energy, then used to perform work. The plates develop the same composition, which reduces the potential of the cell.

Battery maintenance procedures	Inspecting & testing a battery	Batteries come in many sizes and power ratings, so always check the rating of the battery you are servicing.
	Cleaning & replacing a battery	If replacing a smaller battery with a larger one, replace the restraining device and tray used to secure the new battery.
	Charging a battery	Slow charging a battery is less stressful on a battery than fast charging is.