Most of us know the basics of our cars' electrical/ignition systems. Pre-electronic ignition systems were fairly basic; 6 or 12 volt, negative or positive ground, with electricity flowing from the battery to the spark plugs, without computer complications. My cars are non-computer cars and I hadn't realized how complicated automotive electronics had gotten. I have always had an interest in Bentleys, and recently made a study of the S-Z series of 1980-1992. They were redesigned and engineered to create the excitement of the Lemans-winning racing Bentleys of the 1920's. They have a 6.75 Litre V-8, performance suspension system, turbo and one of the greatest burled walnut dash faciae I have ever seen.
I always buy motors manuals first, before buying a car, and when I looked at the Bentley's wiring diagram and a picture of the dash facia removed, showing miles of wiring, dual fuse boxes, sensors and relays, I realized how lucky I am to have such a simple system in my old cars. But, seeing the complexity of the Bentley system made me think about the principles that are the same for all electrical systems, and reviewing these principles might help in understanding more complex systems.
BASIC ELECTRICITY is an invisible force which behaves according to definite rules and procedures, producing predictable effects and results. Scientists have developed the Electron Theoryto explain the nature of electricity.
ELECTRON THEORY vs WATER ANALOGY: If we understand how electricity is supposed to behave in a circuit or unit, we will be more able to diagnose unusual circumstances when electricity malfunctions. The flow and behavior of electricity can be explained by comparing it with the flow of water. It is a good way to explain volts, amps and ohms.
VOLTAGE IS PRESSURE. Using the water analogy, compare a car battery to a water tower. They both provide pressure. The battery is a source of electrical pressure and the water tower supplies water pressure, so think of voltage as electrical pressure. Voltage is what pushes electricity through wires in a circuit, like pressure pushes water through plumbing pipes.
AMPERAGE IS FLOW. Just as water flows through a pipe, electrical current flows through a circuit. Amperage is the electrical unit that tells you how much current is flowing through the wires of a circuit. Amperage is the measure of the rate of current flow A current of one ampere flowing through a wire means that a definite amount of electricity is moving through that wire each second of each minute.
OHMS MEASURES RESISTANCE. Electrical resistance is resistance to the flow of an electrical current. An easy illustration would be that a small wire has more resistance to the flow of electricity than a large wire of the same material. This can also use the water analogy, with the principle of water moving through a small pipe versus a larger one. An ohm is a unit of measurement indicating the amount of resistance to the flow of an electrical current. The amount of current flowing through a wire depends on the electrical pressure or voltage pushing the current and the amount of resistance in the wire. Wires which let current flow easily have low resistance and wires that slow down current flow have high resistance Wire size and length affect resistance in the circuit. The material that the wire is made of also affects the resistance. This is important to remember when you are re-wiring your old car. Six-volt systems carry more amps than do twelve-volt systems, so if you are using 12-volt wire to re-wire a 6-volt system, the general rule is to use a wire two gauges heavier. An example is the old 6-volt harness using a 16-gauge wire, should be re-wired with 12-gauge, 12-volt wire. Short wires offer less resistance than long wires Good conductor materials offer less resistance than poorer conductors. Most of our automotive wires are copper because it is an excellent conductor with very low resistance.
OHMS LAW defines the relationship between volts, amps and ohms. Ohms Law states that VOLTAGE=AMPERAGE x RESISTANCE. Simply put, one volt will push one ampere of current through one ohm of resistance. Ohms Law can be written three ways: Voltage = Amperage x Resistance; Amperage = Voltage + Resistance; Resistance = Voltage + Amperage.
FORCE: To make a circuit operate, we must have electrical pressure. In other words, electromotive force must be applied to produce electrical action in the circuit.
FLOW: The electrical pressure of voltage causes flow (current) and this is what makes things work, such as head lights, ignitions, etc., as current flows through them. As current flows through a circuit, it meets resistance. The pressure must overcome the resistance to make the current flow. The amount of pressure (voltage) applied and the total resistance in the circuit determines how much current will flow.
A CIRCUIT is an electrical path. Batteries and alternators apply electrical pressure and cause an electrical current to move through a circuit from the high pressure to low pressure side. Of course, you must have a complete circuit of wires or other conductors or the current will not flow. If a wire is broken, the current stops.
We will continue next month with the types of circuits and their characteristics.