Presentation on theme: "Chapter 7 Batteries. Objectives (1 of 2) Define the role of a battery in a vehicle electrical system. Outline the construction of standard, maintenance-free,"— Presentation transcript:
Chapter 7 Batteries
Objectives (1 of 2) Define the role of a battery in a vehicle electrical system. Outline the construction of standard, maintenance-free, and gelled electrolyte batteries. Describe the chemical action within the battery during the charging and discharging cycles. Outline how batteries are arranged in multiple battery banks in truck chassis.
Objectives (2 of 2) Verify the performance of a lead-acid battery using a voltmeter, hydrometer, refractometer, and carbon pile tester. Analyze maintenance-free battery condition using an integral hydrometer sight glass. Describe the procedure required to charge different types of batteries. Jump-start vehicles with dead batteries using another vehicle and generator methods. Outline how batteries should be safely stored out of chassis.
Battery-operating Principles A battery is a galvanic device. The lead-acid battery is the electrical energy storage device used on most vehicles. It performs a secondary role as a stabilizer for the voltage in the vehicle electrical system.
42-volt Systems A 42V system is one in which battery voltage is 36 volts and charging pressure is 42 volts. Most manufacturers expect that at least some of their chassis systems will use 42V system voltage before 2010.
Battery Construction Six series connected cells in a polypropylene casing –Each cell has positive (anode) and negative (cathode) plates. –The plates are arranged so that positive and negative plates are located alternately with each other. –Each cell in a battery is separated by partitions.
Electrolyte (1 of 2) It is any substance that conducts electricity. It is the liquid solution that enables the galvanic or chemical action of the battery. It is a solution (mixture) of sulfuric acid (H 2 SO 4 ) and pure water (H 2 O). The solution proportions should be 36 percent sulfuric acid and 64 percent distilled water.
Electrolyte (2 of 2) This produces a specific gravity of at 80° Fahrenheit. The acid-to-water proportions should never be tampered with. During discharge, the ratio of sulfuric acid to that of water is reduced. –This reduces the specific gravity which can be measured with a hydrometer or refractometer.
Specific Gravity and Temperature Temperature directly affects specific gravity. The hydrometer reading must always be temperature adjusted. To adjust specific gravity to temperature: –Add for every 10 degrees above 80° Fahrenheit. –Subtract for every 10 degrees below 80° Fahrenheit. Electrolyte tested using a refractometer does not require temperature correction.
84 Factor Specific gravity relates directly to cell voltage. The 84 factor enables cell voltage to be calculated by adding to the specific gravity measured. If the specific gravity is 1.260, cell voltage would be = volts. The 84 factor is a “ballpark” method that does not apply to discharged batteries.
Discharge Cycle The lead peroxide (PbO 2 ) on the positive plate reacts with the sulfuric acid solution electrolyte (H 2 SO 4 ) releasing an oxygen molecule (O 2 ) to the electrolyte, forming water (H 2 O). The negative plate (Pb) reacts with the electrolyte to form lead sulfate (PbSO 4 ). This chemical action will continue until both the positive and negative plates are coated with lead sulfate (PbSO 2 ) and the electrolyte has been chemically reduced to water (H 2 O).
Charge Cycle The sulfate coatings that have formed on both the positive and negative plates are reacted to return them to the liquid electrolyte. Water molecules in the electrolyte reduce to hydrogen and oxygen. Hydrogen combines with the sulfate in the electrolyte to form sulfuric acid, while the oxygen is drawn to the positive plate to reconstruct the lead peroxide coating.
Sulfation When a battery becomes discharged, both plates are coated with lead sulfate (PbSO4). During the charge cycle, this sulfate coating is converted back into electrolyte. When the sulfate coating hardens on the plates, it can no longer be converted. Battery output then becomes limited and the condition progresses to complete battery failure. A failed battery is said to be sulfated.
Maintenance-free Batteries Substances such as calcium, cadmium, and strontium replace antimony in the plates. –These substances reduce gassing. There is not a means for adding water which has been depleted. A low-maintenance battery is one that uses essentially the same construction as the maintenance-free battery, but does provide for periodic inspection and replenishing of the electrolyte.
Gelled Electrolyte Batteries A special electrolyte is used that liquefies when stirred or shaken, but when left at rest, returns to the gelled state. In the charge cycle of the battery, the oxygen that is released at the positive plate recombines within the cell with the hydrogen released at the negative plate. The recombination of hydrogen and oxygen produces water that is then reabsorbed to the electrolyte.
Battery Ratings Cold-cranking rating –The current load a battery is capable of delivering for 30 seconds at a temperature of 0° F Ampere-hour rating –The amount of current that a fully charged battery can feed through a circuit before the cell voltage drops to 1.75V (For a typical 12V battery, this would be equal to a battery voltage of 10.5V.) Reserve capacity rating –The amount of time a vehicle can be driven with its headlights on in the event of a total charging system failure
Battery Banks Multiple batteries are connected in banks. Batteries may be connected in series or parallel.
Battery Maintenance Neglect and abuse will shorten battery service life. The battery should be inspected at each chassis lubrication. Battery maintenance includes inspecting the battery and its mounting for corrosion, loose mounting hardware, case cracks, and deformation.
Winterizing Batteries When winterizing batteries, disconnect battery cables and load test each battery individually. Because it is important to keep batteries warm to optimize performance in cold weather, many trucks are equipped with battery heaters. If you suspect a battery is frozen, do not attempt to heat it rapidly. –Trickle charge and observe for charge response.
Battery Testing A complete battery test includes these steps: –1. Visual inspection –2. State of charge test –3. Battery capacity (load) test
State of Charge Test (1 of 3) Measure and record specific gravity, corrected to 80°F. If specific gravity readings are or higher and are within 50 points (0.050 specific gravity) between the highest and lowest cells, proceed to the load test.
State of Charge Test (2 of 3) If specific gravity readings are low (below 1.225) or vary more than 50 points between highest and lowest cells, recharge the battery and retest. If, after charging, specific gravity readings are greater than 50 points between highest and lowest cells, replace the battery.
State of Charge Test (3 of 3) Integral hydrometers –On many sealed maintenance-free batteries, a temperature-compensated hydrometer is built into the battery cover. Green dot = 65% or greater charged Dark = 65% of less charge Clear = low electrolyte level
Open Circuit Voltage Test (1 of 3) 1. Remove surface charge; crank the engine for 15 seconds. –Do not allow the engine to start. –To prevent the engine starting, apply the engine stop control or disconnect the fuel solenoid valve lead wire as required. See Table 7-1 on page 195 of textbook.
Open Circuit Voltage Test (2 of 3) 2. After cranking the engine, allow the battery to rest for 15 minutes. 3. Connect the voltmeter across the battery terminals to determine the battery state of charge.
Open Circuit Voltage Test (3 of 3) 4. If the stabilized voltage is below 12.4 volts, the battery should be recharged. Also, inspect the vehicle’s electrical system to determine the cause of the low state of charge. After charging the battery, proceed to the load test.
Electrochemical Impedance Spectroscopy (EIS) EIS evaluates the electrochemical characteristics of a battery by applying alternating current (AC) at varying frequencies and measuring the current response of the battery cell.
Conductance Testing (1 of 2) In the trucking industry, modified EIS testing has become known as conductance testing or AC conductance testing. –These test instruments have been proven to significantly reduce the incidence of incorrectly diagnosed battery problems. The advantages of AC conductance testing are that it is noninvasive and quick, and test instruments are inexpensive.
Conductance Testing (2 of 2)
Charging the Battery There are two methods of recharging a battery: –The slow-charge method –The fast-charge method Either method can be used to recharge most batteries. However, there are some batteries that must be charged slowly.
Caution Hydrogen gas may be discharged during charging and care should always be taken when connecting or disconnecting battery terminals not to create a spark that could result in a battery explosion. Always disconnect the ground cable first and reconnect it last.
Charging the Battery Fast-charging
Shop Talk Frequent need for refilling battery cells is a typical indication that the batteries are being overcharged. Test the charging system and adjust the voltage regulator as needed.
Tech Tip To obtain an accurate reading on a refractometer, it is necessary to view the reading in good light. –Attempting to read a refractometer in poor light will make it difficult to read the refractive scale.
Warning Never jump-start or attempt to recharge a fully discharged maintenance-free battery. –Jump-starting and charging can create an explosion hazard. –These batteries have limited means to vent gas build-up and therefore should be replaced if fully discharged.
Caution Do not overcharge batteries, particularly maintenance-free type batteries. –Overcharging causes excessive boil-off of water from the electrolyte. –Overcharging also causes the battery to produce explosive combinations of hydrogen and oxygen.
Shop Talk Batteries with charger indicators cannot be charged if the indicator is clear or light in color; replace these batteries.
Caution If smoke or dense vapor comes from the battery, shut off the charger and reject the battery. If violent gassing or spewing of electrolyte occurs, reduce or temporarily halt the charging.
Shop Talk Ensure that the vehicle with the dead batteries and the boost vehicle do not directly contact. –If the two vehicles are in contact, a ground connection could be established, which could cause sparking when jumper cables are being connected.
Shop Talk The ground connection must be sound. It used to be recommended that you not connect directly to the ground post of the discharged battery. Due to the sensitivity of electronic control modules connected to the chassis data bus, OEMs today suggest that ground clamps always be connected directly to battery ground.
Warning Make sure that the clamps from one cable do not contact the clamps on the other cable. Wear safety glasses, and do not lean over the batteries when making connections.
Summary (1 of 7) A battery converts chemical energy into electrical energy. A battery is a galvanic device. The storage device for electrical energy on current trucks is the lead-acid battery. A lead-acid battery acts as a sort of electron pump in a truck electrical circuit. A typical battery contains anode (positive) and cathode (negative) plates arranged in cells that are grouped in series within the battery housing. The electrolyte used in lead-acid batteries is a solution of distilled water and sulfuric acid.
Summary (2 of 7) The electrolyte in a lead-acid battery is both conductive and reactive. During the discharge cycle of the battery, lead peroxide on the anode (positive plate) combines with electrolyte, releasing its O 2 into the electrolyte to form H 2 O or water. Meanwhile, lead on the cathode (negative plate) reacts with electrolyte to form lead sulfate (PbSO 4 ). The result of discharging a battery is lead sulfate formation on both the anode and cathode plates.
Summary (3 of 7) During the charge cycle, the sulfate coating on the anode and cathode plates is drawn off and recombined into the electrolyte. –Charging reestablishes the correct proportions of sulfuric acid and water in the electrolyte. A fully charged battery has an electrolyte solution that consists of 36 percent sulfuric acid and 64 percent pure water. A fully charged battery should produce a specific gravity reading of at 80°F.
Summary (4 of 7) During the charge cycle, both oxygen and hydrogen are released from electrolyte in a process known as gassing. –In maintenance-free and low-maintenance batteries, the results of charge gassing are contained in a condensation chamber. Gel cell batteries are designed to sustain deep cycling and are used in truck electrical systems requiring an isolated battery to power auxiliary accessories during shutdown. Gel cell batteries should be recharged by direct connection to the battery charger.
Summary (5 of 7) Only approved chargers may be used to charge gel cell batteries. –These regulate the charging voltage to between 13.8V and 14.1V. Most battery chargers use a charging voltage of about 16V, which can destroy a gel cell battery. On trucks equipped with gel cell batteries, the voltage regulator must be set at 14.1V or less. Voltages higher than 14.2V can destroy gel cell batteries. Batteries are performance rated by cold-cranking amps, reserve capacity, and ampere-hour rating.
Summary (6 of 7) Most truck batteries are specified to a chassis electrical system by their cold-cranking amp (CCA) rating. Temperature has to be considered when evaluating the output capacity of any battery. –Available cranking power significantly drops as temperature falls. When removing a battery from a vehicle, always disconnect the ground cable first. Battery electrolyte should be tested with either a refractometer or a hydrometer.
Summary (7 of 7) When jump-starting vehicles, be sure to study the battery configuration on both vehicles before attempting to make electrical connections. Also switch off all the chassis electrical loads before connecting jumper cables. Generator charging is popular and effective, but ensure that the correct procedure is followed before using this method of charging. Capacitance testing using instruments such as the Midtronics 700 is commonly used to assess battery serviceability. Battery performance is best tested using a digital AVR.