Electrical Principles: 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.
	Semiconductors	Semiconductors are widely useful because their conductivity can be manipulated and precisely controlled – by such means as introducing impurities, or an electric field, or just light.
	Ground	Ground is a term used to indicate connecting a component to the vehicle frame or chassis.
	Ohm's law calculations	Ohms Law states that: I = V/R where I is the current in amperes, V is the potential difference in volts, and R is a resistance, measured in ohms. 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. If an electrical component has a rating in Watts, it will be a measurement of power consumption. To calculate power: P = I x E or Watts = Amps x Volts.

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.

Effects of electricity	Heating effects	Electricity can be transferred into other forms of energy such as the heat which generates light in headlight bulbs.
	Chemical effects	Electricity may be used to store energy through chemical reactions such as in a lead acid battery.
	Magnetic effects	Current passed through a coil of wire creates a magnetic field. Turning the current on and off can activate a mechanical relay, or create the rotary motion of an electric motor.
	Electrical resistance	Electrical resistance is the measure of how much an object resists the passage of an electrical current. Resistance is measured in ohms.

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.
	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.

Electrical testing procedures	Using a non-powered test light	Non-powered test lamps are very useful to determine a live part of a circuit. The objective of this procedure is to show you how to use a non-powered test light.
	Using a lead light	Also known as drop lights or utility lights, the light a lead light produces can make locating components and faults easier and more accurate. The objective of this procedure is to show you how to demonstrate the correct method of operating a lead light.
	Using a DVOM to measure continuity	The objective of this procedure is to show you how to use 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	The objective of this procedure is to show you how to use 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 two surfaces, separated by insulating material. When the capacitor is charged, one surface is positively charged, the other is negatively charged.
	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. The type of shielding used can be one of three forms: twisted pair, Mylar tape and drain lines.
	Wire sizes	There are two scales used to measure the sizes of wires: Metric and AWG (American Wire Gauge).
	Length vs. resistance	As the length of the wire increases, so does the resistance within the wire. Therefore the greater the length of the wire, the larger the cross-sectional area needs to be.
	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.
	Ballast resistor	The ballast resistor is used to reduce the voltage to the ignition coil during normal running conditions.

Wires & connectors procedures	Stripping wire insulation	The objective of this procedure is to show you how to correctly strip an electrical wire and connect a solderless connector. Always use the correct tool for stripping the insulation from a wire, it is much safer and more effective.
	Installing a solderless terminal	There are different types and sizes of wire terminals, but the procedure for installing all of them is the same. The objective of this procedure is to show you how to correctly strip an electrical wire and connect a solderless terminal.
	Soldering wires & connectors	Solder is applied with a hot soldering iron. Solder is available as solid or flux cored. Solid solder requires an external flux to be applied in the soldering process. The objective of this procedure is to show you how to correctly solder an electrical connection to an electrical wire.

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.
	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 semiconductor resistors. Their resistance changes according to their temperature and they are used to control many electrical items in the automobile.
	Transistors	Transistors are used as switches, and to amplify currents. The two types of transistor are 'npn' and 'pnp'.

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-weight 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. The objective of this procedure is to show you how to inspect and test a battery.
	Cleaning & replacing a battery	The objective of this procedure is to show you how to clean and replace an automotive battery. The first step is to disconnect the battery, always removing the clamp from the negative terminal first.
	Charging a battery	The objective of this procedure is to show you how to correctly charge a battery using battery charging equipment. Before charging a battery always carry out a visual inspection of the battery to ensure there are no cracks or holes in the casing.

Topic group	Topic	Summary