How a Battery Functions

Electrical System Introduction

Electricity is used to perform a vast number of procedures and operations. For instance, an automobile’s electrical system operates the starter motor to crank the engine; it makes the sparks that ignite the compressed air-fuel mixture; it operates the radio, the lights, the horns, and many other devices including computerized units. This article will describe both the nature and the fundamentals of electricity.

Electricity

All things are made up of extremely small particles known as atoms. The atom itself is made up of smaller particles such as protons and electrons. An proton is a positively (+) charged particle, and an electron is a negatively (-) charged particle.

In certain types of materials — i.e., conductors — electrons can be detached from their atoms, becoming free electrons with the ability to flow. Such a flow is known as an electrical current, and when many electrons are flowing, the current will be high. Conversely, when few are flowing, the current will be low. A large number of flowing electrons will be required to produce an electric current which is strong enough to do work.

In order to have current, you must also have voltage. Specifically, voltage is the force or pushing power of the electricity.

An electrical power source such as a battery or a generator is used to supply voltage. These power sources can force all flowing electrons to move in the same direction. When a current of a sufficient rate is produced, enough energy will be available to illuminate lights or to turn motors, etc.

Current

An electrical current is a mass movement of electrons through a conductor. The number of electrons passing any given point in the circuit in one second determines the amount of current, which is measured in amperes (A or Amps).

It is important to realize that the direction of current does not coincide with the direction in which the electrons are flowing. In earlier days, it was believed that electricity actually flows from the positive terminal to the negative terminal in a circuit. It was subsequently discovered, however, that electrons actually flow in the opposite direction. Since it was too late (and too dangerous) at that stage to reverse the definitions of positive and negative, it is still held that current flows from positive to negative while electrons actually flow from negative to positive.

The following figure illustrates a simple circuit utilizing a battery as its power source. As soon as the circuit is closed, electrons will flow from the negative terminal to the positive terminal of the battery. Note that the current is indicated as flowing from positive to negative.

Voltage

Current flow is produced by having a difference in electrical potential — or, in other words, electrical pressure — at each end of a conductor. If one end has surplus electrons while the other end is lacking electrons, a pressure differential, or voltage, will arise and a current will be caused to flow. In order to keep the current flowing, it is necessary to maintain the voltage. Degrees of voltage are measured in volts (V).

In a vehicle’s electrical system, voltage is supplied either from a battery or from an alternator.

Resistance

When current flows in a circuit, it will come up against a certain degree of resistance. The greater the resistance, the harder it will be for the current to continue to flow. Resistance is measured in ohms.

Electricity must push against the resistance in a circuit in order to do any kind of work, such as generating heat, producing light, or moving objects to a new location. A circuit’s electrically-operated devices generally have a certain degree of resistance and these essentially constitute loads in the circuit. In a circuit which is operating normally, the load is usually the only measurable source of resistance.

Conductors and Insulators

Materials with a great number of free electrons are called conductors. In most electrical circuits, copper is widely used as a conductor since its resistance is extremely small and it is relatively inexpensive. Vehicle bodies are also considered as conductors and usually form part of the vehicle’s overall electrical system.

Materials with extremely large resistances are called insulators. In addition, many conductors are covered or isolated with insulators made of glass, ceramics, plastics, rubber, fiber, etc. Insulation prevents electricity from escaping and ensures the flow of current along the correct path. 

Magnets

Magnetism and electricity are closely related. At this point, however, it is sufficient to remember just two important facts about magnets:

1. Electricity can produce magnets.
2. Magnets can produce electricity.

Electrically produced magnets are called electromagnets, and it is widely known that magnets attract iron. Magnetic components such as solenoids, relays, and motors are essentially devices that convert electric energy into motion.

Magnets are also used in the generation of electricity. The electromagnet inside the alternator helps to convert rotating motion into electricity.

Direct Current (DC) and Alternating Current (AC)

Electrical current can be classified into two major types — namely direct current (DC) and alternating current (AC). In a DC circuit, current will always flow in the same direction. In an AC circuit, however, the direction of current flow switches back and forth many times per second.

The power source which is employed in a circuit will determine whether AC or DC will be generated. Batteries provide DC; consequently, automotive electrical systems are based on DC circuits. However, automobiles are usually equipped with AC generators (i.e., alternators) since these are more effective than DC generators. AC generated by the alternator is rectified and regulated into DC which is suitable for supply to the electrical system and for charging the vehicle’s battery.

Power outlets in homes and workshops usually provide AC.

Automotive Circuit Fundamentals

Every vehicle contains dozens of electrical circuits — some may look quite complicated, but they all operate on the same basic principles.

Circuits consist of many components, and most vehicle electrical systems comprise the following:

• Power sources such as the battery and the alternator
• Protection devices such as fuses and circuit breakers
• Control devices such as switches and relays
• Loads such as light bulbs and motors
• Conductors such as cables and wires
• A ground which is usually the vehicle’s chassis

All circuits must form a complete loop. Regardless of the number of paths or the location of components, current must flow in a closed loop from the positive battery terminal, though the components to ground, and finally back to the negative battery terminal. Some circuits have just one path, while others have several paths and several loads as shown in the simplified diagram below. 

Schematic Symbols Used in Shop Manual

Shop Manual are important tools for carrying out maintenance on vehicle electrical equipment. Proper use of Shop Manual during service and repair work will allow the required information to be located quickly and efficiently.

Shop Manual contain circuit diagrams that show both the relative positioning of parts and how these parts are connected. Diagrams of the entire electrical systems will be provided, as will diagrams of smaller sub-systems. Using these system diagram, the location of electrical operations can be easily identified.

Major schematic symbols which are used in Shop Manual are shown below.