An automotive battery is an electrochemical device that provides for and stores electrical energy. Electrical energy is produced in the battery by the chemical reaction that occurs between two dissimilar plates that are immersed in an electrolyte solution. An automotive battery has the following important functions: It operates the starting motor, ignition system, electronic fuel injection, and other electrical devices for the engine during cranking and starting. It supplies all the electrical power for the vehicle accessories whenever the engine is not running or at low idle. It furnishes current for a limited time whenever electrical demands exceed charging system output. It acts as a stabilizer of voltage for the entire automotive electrical system. It stores energy for extended periods of time. Electrical loads that are still placed on the battery when the ignition switch is in the OFF position are called key-off or parasitic loads. The amount of electrical energy that a battery is capable of producing depends on the size, weight, and active area of the plates and the specific gravity of the electrolyte solution. The conventional battery is constructed of seven basic components: Positive plates. Negative plates. Separators. Case. Plate straps. Electrolyte. Terminals. Electrolyte solution used in automotive batteries consists of 64% water and 36% sulfuric acid by weight. The electrolyte solution causes the chemical actions to take place between the lead dioxide of the positive plates and the sponge lead of the negative plates. The electrolyte is also the carrier that moves electric current between the positive and negative plates through the separators. The automotive battery has a fully charged specific gravity of 1.265 corrected to 80°F. Grid growth is a condition where the grid grows little metallic fingers that extend through the separators and short out the plates. Deep cycling is discharging the battery almost completely before recharging it. In a conventional battery, the positive plate is covered with lead peroxide and the negative plate is covered with sponge lead. In maintenance-free batteries, the cell plates contain calcium, cadmium, or strontium to reduce gassing and self-discharge. The grid construction of the hybrid battery consists of approximately 2.75% antimony alloy on the positive plates and a calcium alloy on the negative plates. The recombination battery uses separators that hold a gel-type material in place of liquid electrolyte. Absorbed glass mat (AGM) batteries hold their electrolyte in a moistened fiberglass matting that is sandwiched between the...

Read

FIGURE. Different types of battery hold-downs. All batteries must be secured in the vehicle to prevent damage and the possibility of shorting across the terminals if the battery tips. Normal vibrations cause the plates to shed their active materials. Hoiddowns reduce the amount of vibration and help increase the life of the battery. FIGURE. Some vehicles are equipped with a heat shield to protect the battery from excessive heat. In addition to hoiddowns, many vehicles may have a heat shield surrounding the battery. This heat shield is usually made of plastic and prevents under-hood temperatures from damaging the battery. Note: It is important that all hold-downs and heat shields be installed to prevent early battery failure.

Read

Battery cables are high-current conductors that connect the battery to the vehicles electrical system. Battery cables must be of a sufficient capacity to carry the current required to meet all electrical demands. Normal 12-volt cable size is usually 4 or 6 gauge. Various forms of clamps and terminals are used to assure a good electrical connection at each end of the cable. Connections must be clean and tight to prevent arcing, corrosion, and high-voltage resistance. FIGURE. The battery cable is designed to carry the high current required to start the engine and supply the vehicle's electrical systems. The positive cable is usually red (but not always), and the negative cable is usually black. The positive cable will fasten to the starter solenoid or relay. The negative cable fastens to ground on the engine block or chassis. Some manufacturers use a negative cable with no insulation. Sometimes the negative battery cable may have a body grounding wire to help assure that the vehicle body is properly grounded. Note: It is important to properly identify the positive and negative cables when servicing, charging, or jumping the battery. Do not rely on the color of the cable for this identification; use the markings on the battery case. Note: Pinch on battery cable clamps are a temporary repair only!

Read

Battery capacity ratings are established by the Battery Council International (BCI) in conjunction with the Society of Automotive Engineers (SAE). Battery cell voltage depends on the types of materials used in the construction of the battery. Current capacity depends on several factors: The size of the cell plates. The larger the surface area of the plates, the more chemical action that can occur. This means a greater current is produced. The weight of the positive and negative plate active materials. The weight of the sulfuric acid in the electrolyte solution. The battery's current capacity rating is an indication of its ability to deliver cranking power to the starter motor and of its ability to provide reserve power to the electrical system. The commonly used current capacity ratings are explained in the following sections. Ampere-Hour Rating The ampere-hour rating is the amount of steady current that a fully charged battery can supply for 20 hours at 80°F (26.7°C) without the terminal voltage falling below 10.5 volts. For example, if a battery can be discharged for 20 hours at a rate of 4.0 amperes before its terminal voltage reads 10.5 volts, it would be rated at 80 ampere-hours. This method of battery rating is not widely used. Cold Cranking Rating Cold cranking rating is the most common method of rating automotive batteries. It is determined by the load, in amperes, that a battery is able to deliver for 30 seconds at 0°F (-17.7°C) without terminal voltage falling below 7.2 volts (1.2 volts per cell) for a 12-volt battery. The cold cranking rating is given in total amperage and is identified as 300 CCA, 400 CCA, 500 CCA, and so on. Some batteries are rated as high as 1,100 CCA. Cranking Amps Cranking Amps (CA) is an indication of the battery's ability to provide a cranking amperage at 32°F (0°C). This rating uses the same test procedure as the cold cranking rating or CCA discussed earlier, except it uses a higher temperature. To convert CA to CCA, divide the CA by 1.25. For example, a 650-CCA-rated battery is the same as 812 CA. It is important that the technician does not misread the rating and think the battery is rated as CCA instead of CA. Reserve-Capacity Rating The reserve-capacity rating is determined by the length of time, in minutes, that a fully charged battery can be discharged at 25 amperes before battery voltage drops below 10.5 volts. This rating gives an indication...

Read

FIGURE. The most common types of automotive battery terminals. Terminals provide a means of connecting the battery plates to the vehicle's electrical system. All automotive batteries have two terminals. One terminal is a positive connection; the other is a negative connection. The battery terminals extend through the cover or the side of the battery case. The following are the most common types of battery terminals: Post or top terminals: Used on most automotive batteries. The positive post will be larger than the negative post to prevent connecting the battery in reverse polarity. Side terminals: Positioned in the side of the container near the top. These terminals are threaded and require a special bolt to connect the cables. Polarity identification is by positive and negative symbols. L terminals: Used on specialty batteries and some imports.

Read

FIGURE. Ultra-capacitor cell construction. Ultra-capacitors are capacitors constructed to have a large electrode surface area and a very small distance between the electrodes. Unlike conventional capacitors that use a dielectric, the ultra-capacitors use an electrolyte. It also stores electrical energy at the boundary between the electrodes and the electrolyte. Although an ultra-capacitor is an electrochemical device, no chemical reactions are involved in the storing of electrical energy. This means that the ultra-capacitor remains an electrostatic device. The design of the ultra-capacitor increases its capacitance capabilities to as much as 5000 farads. Ultra-capacitors are used in many present-day hybrid vehicles and in some experimental fuel cell EVs because of there ability to quickly discharge high voltages and then be quickly recharged. This makes them ideal for increasing boost to electrical motors during times of acceleration or heavy loads. Ultra-capacitors are also very good at absorbing the energy from regenerative braking.

Read

Automotive manufactures have been investigating the use of high-voltage batteries for over 20 years. The first step was to the use of 42-volt systems. Today, high-voltage batteries are required by electric-drive vehicles. This section discussed the high-voltage battery system and its progression. 42-Volt Systems The first production vehicle that used the 42-volt system was the 2002 Toyota Crown Sedan, which was only sold in the Japanese market. Although the use of 42-volt systems is very limited at the current time, the technology learned has been applied to the electric hybrid systems. As you have probably come to realize, the increased use of electrical and electronic accessories in today's vehicles has about tapped the capabilities of the 12-volt/14-volt electrical system. Electronic content in vehicles has been rising at a rate of about 6% per year. It's been estimated that by the end of the decade the electronic content will be about 40% of the total cost of a high-line vehicle. The electrical demands on the vehicle have risen from about 500 watts in 1970 to about 4,000 watts in 2005. It is estimated that in 10 years the demand may reach 10,000 watts. Note: The reason for using 42 volts is based on the current 12-volt system. Today's batteries are rated at 12 volts but actually store about 14 volts. In addition, the charging system produces about 14 to 15 volts when the engine is running. With the engine running, the primary source of electrical power is the charging system. This means that the automobile's electrical system is actually a 14-volt system. Forty-two volts represent three 12-volt batteries, but since they actually hold a 14-volt charge, the system is considered 42 volts (3 times 14 volts equals 42 volts). An additional benefit that may be derived from the use of a 42-volt system is it allows manufacturers to electrify most of the inefficient mechanical and hydraulic systems that are currently used. The new technology will allow electromechanical intake and exhaust valve control, active suspension, electrical heating of the catalytic converters, electrically operated coolant and oil pumps, electric air conditioning compressor, brake-by-wire, steer-by-wire, and so on to be utilized. Studies have indicates that as these mechanical systems are replaced, fuel economy will increase by about 10% and emissions will decrease. Additional fuel savings can also be realized due to the more efficient charging system used for the 42-volt system. Current 14-volt generators have an average efficiency across the...

Read