Electrical System
The automotive electrical system consists of various wires, lights, circuits, fuses, relays, and switches. Even though the electrical system is extremely complex, there are still many repairs that you can do without taking your vehicle to a service facility. A simple thing like a headlight burning out can stop you from driving safely down the road. At some point in time most people will have to jump-start a vehicle, yet many are scared of the procedure. This section provides the basics of how to maintain, test, and repair various electrical system components.

Electrical Terms
Electricity can be defined as the movement of electrons in a conductor. Copper is a well known conductor. Electrons orbit the nucleus of an atom much like the moon goes around the earth. Electricity flows through a conductor, which is usually in the form of a wire covered by an insulator. An insulator, such as plastic, is something that restricts the flow of electrons. Before discussing the electrical system, you need to be able to identify and describe three main terms: voltage, current, resistance.

Voltage
A volt is the measure of voltage or pressure pushing electrons. Compare this to a faucet in your home. When the faucet is off there is still potential to flow, but the valve holds back the pressure. Voltage is the electrical pressure that causes current to flow. In technical terms, one volt is the amount of pressure required to move one ampere of current through a resistance of one ohm. (Amps and ohms will be discussed later.) Most vehicles have 12-volt systems, while most homes have 120-volt systems. Another difference in most home and vehicle electrical systems is the current. Automotive batteries are DC (Direct Current) while homes use AC (Alternating Current).

Current
Amperage is the unit used to measure electrical current. Current can be described as the quantity of electrons moving through a conductor. There are two types of electrical current: Direct Current (DC) and Alternating Current (AC). In DC systems the electrons are moving through the conductor in one direction. In AC systems the electrons change direction at a given rate of time. The alternator in a vehicle generates AC, but then converts the current to DC to recharge the battery.

Resistance
An ohm is a measure of electrical resistance. The resistance in a circuit is usually a load such as a light, radio, electrical motor, or sensor. For example, there needs to be resistance in the filament of a light bulb for it to produce light. Ohm’s Law shows the direct relationship between volts, amps, and ohms. Ohm’s law states that: Voltage = Current x Resistance. This simple mathematical equation can be used to find one unknown variable if any two of the other variables are known.

Starting System
The starting system converts chemical energy (molecular energy) to electrical energy (electrons moving through a conductor) to mechanical energy (energy of motion). The starting system consists of basically five components: battery, key switch, solenoid, starter, and neutral safety switch.

Battery
The purpose of the battery in a vehicle is to store chemical energy, supply electrical energy to the starter when the engine is cranking, and supplement the alternator in running various accessories (e.g., lights, radio, etc.). Most automotive batteries are 12 volts DC. The battery stores energy in a chemical form. In the starting system, the battery converts the chemical energy to electrical energy when the operator turns the key switch to start the engine.

Key Switch
A switch is a unit that can connect or disconnect electrical current from flowing. The key switch is the unit that is turned to start the engine. Usually located on the steering column, the key switch completes the circuit of electrical current to the starter solenoid.

Solenoid
A solenoid is another type of switch. It is called an electromechanical switch. The key switch sends electrical current to the solenoid. Without the solenoid large amounts of current would have to go through the key switch. The solenoid is placed in the electrical circuit to switch from a low current to a high current. A small amount of electrical current energizes a coil within the solenoid, which creates a magnetic field. This closes the circuit for the higher current to go to the starter. The solenoid can either be located on the inside fender wall of the vehicle or mounted on or near the starter.

Starter
After the current goes through the solenoid it reaches the starter. The starter is an energy converter. The starter converts electrical energy to mechanical energy to crank over the engine. The starter uses a small gear that meshes with the vehicle’s flywheel gears. The flywheel is connected to the crankshaft. The starter is usually mounted on the underside of the engine.

Neutral Safety Switch
The neutral safety switch only allows current to flow in the starting system if the clutch is depressed (manual transmission) or if the vehicle is in park or neutral (automatic transmission). This prevents the possibility of the vehicle being started while in gear.

Charging System
The charging system is somewhat a reverse of the starting system. The charging system converts mechanical energy to electrical energy to chemical energy. The charging system keeps the battery recharged. The four main components of the charging system are: alternator drive belt, battery, alternator, and voltage regulator.

Alternator Drive Belt
The alternator drive belt turns the pulley on the alternator. Sometimes also referred to as a fan belt, the alternator drive belt may or may not be connected to other accessories such as the power steering pump, water pump, fan, air conditioning, and air pump. Belts come in two types: serpentine and “v”. A serpentine belt, also called a multi-ribbed belt, is flat on one side and has grooves that run parallel with the belt. Commonly, serpentine belts will have between 2 to 8 grooves on one side. Serpentine belts are usually ½ to 1 inch wide depending on the number of grooves and automotive application. In contrast, a v-belt is usually less than ½ inch in width and has a cross-section that looks like a “v”.

Battery
The battery is part of the charging system as well as the starting system. It is called a 12-volt DC battery, but actually should maintain about 12.6 volts when fully charged. The battery converts electrical energy to chemical energy (and vice versa). The battery stores energy for future use.

Alternator
The drive belt rotates the alternator pulley, which then turns a shaft in the alternator. The alternator converts mechanical energy to electrical energy. Initially it converts the electricity to alternating current, but the end result is direct current. Diodes are used in the alternator to make the conversion from AC to DC current.

Voltage Regulator
The voltage regulator is commonly located in or near the alternator. It does basically what the name suggests; it regulates the electrical pressure (voltage). Common voltage from the regulator while the engine is running is 14.5 volts. If the regulator does not hold electrical pressure at or near 14.5 volts, the battery could be overcharged or undercharged by the alternator.

Battery Performance Ratings
When purchasing an automotive battery it is important to identify the correct battery for your vehicle. Besides being the correct physical size, a battery must meet the amperage requirements to start the engine and run accessories. When comparing batteries from different vendors make sure you are comparing the same type of rating. Battery manufacturers basically use two ratings: cold-cranking amps and cranking amps.

Cold-Cranking Amps
A battery that is rated with cold-cranking amps has been tested to deliver the specified number of amperes at 0 degrees Fahrenheit for a duration of 30 seconds.

Cranking Amps
A battery that is rated with cranking amps has been tested to deliver the specified number of amperes at 32 degrees Fahrenheit for a duration of 30 seconds.

Fuses
A junction block containing fuses can be found under the dash or under the hood. A cover on the junction block often identifies the purpose of each fuse. If the cover is unclear, refer to your owner’s manual for a fuse diagram. Fuses are used in electrical circuits to safeguard the vital components. A fuse will blow if too much current is trying to get to the intended load. Fuses are rated in amps such as: 5, 10, 15, 20, 25, 30, etc. Never replace a blown fuse with a larger amperage rating. A fuse is rated so it is the weakest link in the electrical circuit. If a blown fuse is replaced with a larger amp rated fuse severe electrical damage could result. Fuses can be broken down into two types: glass cylinder and blade style. Most vehicles from the 1980s and newer use the blade style fuse. Some vehicles use a smaller blade style fuse called a mini-fuse. Always consult your owner’s manual for fuse specifications.

Lights

Lights are an important safety feature in a vehicle. Without them we could not see at night or notice when someone is braking or turning ahead. The activity on the attached CD will guide you in replacing and testing bulbs and headlamps. Lights burn out with age. Miniature light bulbs (e.g., taillights, brakelights, sidemarkers, etc.) come in various types: bayonet, screw-in, and push-in. Headlights usually come in two types: composite and sealed beam. When a light has the word halogen printed on it, it indicates that inside the bulb is a gas, which results in a brighter light.

Summary

The electrical system may seem quite complex to the do-it-yourselfer, but there are simple ways to maintain it and save money. The starting system converts chemical energy to electrical energy to mechanical energy in order to start the engine. The charging system converts mechanical energy to electrical energy to chemical energy to recharge the battery. Fuses are over-current protection devices. Lights are used in many places on the automobile and periodically need replacing.

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