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Initial Print Date: 5/01 Revision Date: Subject Page Battery Construction 4 Battery Types 7 How The Battery Works 8 Common Battery Terms 10 Battery Testing 12 Battery Maintainence 15 Battery Replacement 21 Special Battery Systems 25 Closed Circuit Current Draw Testing 32 Review Questions 35 Table of Contents The Battery 2 The Battery The Battery Model: All Production Date: All Objectives After completing this module you should be able to: • Explain the battery components and construction. • Understand the different types of batteries. • Explain the chemical process of charging and discharging. • Know common battery terms. • Perform battery testing. • Properly charge a battery. • Know the procedures for the Battery Log Form. • Understand dual battery systems. 3 The Battery All things electrical start at the Battery 4 The Battery The Battery Purpose of the Automotive Battery The battery is the primary EMF source in the automobile. In addition the battery performs the following functions: • Provides voltage and current for the starter motor. • Provides voltage and current for the ignition during cranking. • Supplies all electrical power when the charging system is not operating. • Supplies the extra power necessary when the vehicle’s electrical load exceeds the supply from the charging system. • Acts as a voltage stabilizer in the electrical system. The battery evens out voltage spikes and prevents them from damaging other components in the electrical system. • Provides power to KL30, KL15 and KLR. The battery does not store electrical energy. It stores chemical energy that is converted to electrical energy as it discharges. Battery Construction Modern automotive batteries are made of cases (usually plastic) containing alternating plates of Lead and Lead Dioxide (or Lead Oxide) separated by insulators. These alternating plates are connected in series to produce a volt- age of 12.6 volts, or about 2.1 volts for each set of Lead and Lead Dioxide plates. The negative terminal is connect- ed to a Lead Dioxide plate and the positive terminal to a Lead plate. The plates are covered with electrolyte which is a solution of 35% Sulfuric acid and 65% Water. 1. Plastic container. 2. Positive and negative internal plates made of lead. 3. Plate separators made of porous synthetic material. 4. Electrolyte which is a dilute solution of Sulfuric acid and water better known as Battery Acid. 5. Lead terminals which are the connection point between the battery and whatever it powers. 5 The Battery Battery Case Most battery cases and their covers are made of polypropylene. The case is divided into six sections or cells, shaped similar to an ice-cube tray. The case is designed to: • Withstand hot and cold temperature extremes. • Resist damage caused by mechanical shock in automotive applications. • Resist acid absorption and chemical damage. The Grids The grids are the supporting framework for the active material of the plates. They also con- duct current to and from the active material plates. The Plates Plates are grids covered with a paste mixture of Lead Oxide and Sulfuric Acid and water. An expander material made of powdered sulfates is added to the paste to produce negative plates. A forming charge is applied to the positive plates converting the Lead Oxide to Lead Dioxide, a highly porous material which allows the electrolyte to freely penetrate the plate. A forming charge is also applied to the negative plates converting the Lead Oxide to Sponge Lead. The Sponge Lead allows the electrolyte to penetrate freely allowing the material beneath the plate surface to take part in the chemical reaction. The Separators Separators are thin sheets of electrically insu- lating porous material used as spacers between the plates to prevent short circuits within the cells. Fine pores in the separators allow ionic current flow in the electrolyte between the positive and negative plates. 5510108.gif 6 The Battery Elements In the most common method of construction, a stack of alternate positive and negative plates are formed with separators between each positive and negative plate. The lugs of the negative plates are welded together as are those of the positive plates. The plate strap of each group of plates is used to connect them in series with the plate group of the next cell, or with a battery terminal. The assembly resulting from placing one positive plate group and one negative plate group together, with separators is known as an element. There is one element per battery cell. More or larger plates per cell will increase plate surface area and increase capacity of the battery but will not affect the voltage output. Electrolyte The electrolyte is a mixture of Sulfuric Acid and Water. Electrolyte consists of 35% sulfuric acid and 65% water. The electrolyte is the carrier for the electric current to move between the positive and neg- ative plates through the separators. The Lead Terminals BMW’s use a tapered top terminal. This design uses tapered terminal posts built to indus- try standards so that all cable clamps will fit any battery with these posts. The positive terminal is slightly larger than the negative to minimize the danger of installing the battery in reverse. The positive terminal is 17.5mm in diameter at the top. The negative terminal is 15.9mm at the top. 5510170.jpeg 15.9 mm 17.5 mm Positive + Negative - 7 The Battery Battery Types There are at least three types of the Lead-acid batteries that are currently used in the Automotive Industry. Lead-Acid Battery The three major contributors to battery chemistry are lead, lead dioxide and sulfuric acid. Pure lead is too soft to withstand the physical abuse of mobile applications, so a strenght- ener is needed. About 6% antimony, a semi metallic element produced as a by-product to copper and lead ore refining, is added to strengthen the lead. The antimony added to the grids acts as a catalyst and makes the loss of hydrogen and oxygen through outgassing worse. These batteries require frequent water replenishing. Lead/Calcium Battery Introduced in the 1970’s Lead/Calcium batteries have Calcium added to the positive and negative grids to reduce the outgassing. These batteries were first referred to as “mainte- nance free”. The Lead/Calcium batteries are not resistant to deep-cycling which occurs when a battery is drained to a very low voltage before being recharged. Frequent deep- cycling renders these batteries unable to sustain a charge. Lead/Calcium batteries need to be charged at higher voltage settings or they will not be recharged to full capacity. Hybrid Battery Hybrid batteries use a positive grid strengthened with antimony and a negative grid with calcium. The hybrid battery is more resistant to deep cycling than the lead/calcium, but still not as good as the original Lead-acid battery. Water usage is greatly reduced in the hybrid battery, although regular checking is advisable. Most cars supplied with hybrid batteries have their voltage regulators set to 14.3 volts. Hybrid batteries were first installed in the E30 convertible (SIB 61 12 91) during the 1991 Model Year. 8 The Battery How The Battery Works Discharging Batteries don’t store electrical energy, they store chemical energy and convert it to electri- cal energy during the discharging process. Each cell of a battery contains positive and negative plates (grids). The positive plate is made of lead dioxide, the negative plate of a spongy lead. The negative plate combines with the sulfuric acid to create lead sulfate and one extra electron. The positive plate pro- duces hydrogen ions and sulfuric acid ions (positive ions, atoms missing one electron). The extra electrons from the negative plate are passed from the negative battery terminal and through the electrical consumer, back to the positive battery terminal. Once back at the battery, the free electrons combine with the positive ions at the positive battery termi- nal producing lead sulfate and water. It is important to remember that the system is closed. For every electron generated at the negative terminal, there is an electron consumed at the positive terminal. As the process continues, the active materials (lead and lead dioxide plates and the elec- trolyte) become depleted and the reactions slow down until the battery is no longer capa- ble of supplying electrons. At this point the battery is discharged. The discharge process changes the ratio of sulfuric acid to water in the electrolyte, as more water is produced in the discharge process. By measuring the volume of acid in the water, the state of charge of the battery is discovered. 5510161.jpeg Starter Radio Horn Lights Ignition Positive Lead peroxide changing to Lead Sulfate Negative Sponge lead changing to Lead Sulfate. Electrolyte The sulfate of sulfuric acid unites with active material on plates leaving water and acid solution. Hydrogen of acid and oxygen of lead peroxide combine to form water diluting solution. Discharge Process 9 The Battery Charging Applying voltage to the battery from an external source such as the generator or battery charger reverses the chemical action in the battery. Reversing the chemical action in the battery, forces the free electrons at the negative ter- minal of the battery back into the electrolyte raising the sulfuric acid percentage. This chem- ical action removes the Lead sulfate that had formed on the negative plates leaving pure active material. The electrons that were forced into the electrolyte are able to react with the lead sulfate on the positive terminal again raising the Sulfuric acid content and leaving pure active materi- al on the positive plates. This process enables the battery to be used over and over again. 5510160 Charging Process Positive Plate Lead sulfate changes to lead peroxide. Sulfate returns to electrolyte Negative Plate Lead sulfate changes to sponge lead. Sulfate returns to electrolyte Very dilute electrolyte made stronger by return of sulfate from plates. 10 The Battery Common Battery Terms • Ah -Amp Hour Capacity This rating is derived from discharging a fully charged battery at a constant amp draw for 20 hours @ 80o F, without the voltage of the battery falling below 10.5 volts. The constant amp draw is multiplied by the 20 hours to come up with the Amp Hour Rating. • CCA -Cold Cranking Performance Represents the amperage capacity a fully charged battery can deliver @ 0o F for 30 seconds before the voltage of the battery falls below 7.2 volts. • RC -Reserve Capacity Reserve capacity is expressed in minutes and relates to the amount of time a fully charged battery can maintain a constant draw of 25 amps @ 80o F before the voltage falls below 10.2 volts. • W -Watts The measurement of electrical power that the battery can deliver for a cold start. It is calculated by multiplying the starter amperage draw @ 0o F times 10 volts. • V -Volt Unit of measure of potential difference (Electrical pressure). • A -Amp The current flow in a circuit. Value is proportional to the number of electrons flowing past a point in one second. • � -Ohm The measurement of the resistance of a component or circuit to current flow. Teile-Nr. (Part No.) 61021 6 902 796 12V 55AH 480A EN 555 080 048 12V 90RC 425CCA SAE Group No . 47 fur Ersatz (for replacement): Teile - Nr. 61 21 6 902 796 Nass (wet) 95101104.eps 11 The Battery • Electrolyte The mixture of sulfuric acid and water. 35% sulfuric acid, 65% water. • Specific Gravity The measurement (by weight) of the volume of sulfuric acid in the electrolyte. A specific gravity of 1.275 (the specific gravity of a fully charged battery) means that the electrolyte is 1.275 times heavier than water. The specific gravity of water is 1.000. • Sulfate Deposits formed on the plates of the battery as the electrolyte gives up its sulfuric acid. Excessive deep cycling of a battery can cause a hardening of this deposit and make it impossible to return sulfate to the electrolyte. A sulfated battery is one which has these hardened deposits on the plates and cannot be recharged to full capacity. • OCV Open Circuit Voltage The measurement of the voltage of a battery across the terminals. Notes Original BMW Teile-Nr.(Part No.) 61 21 8 381 762 12V 90Ah 720A EN 590 051 072 12 V 175C 850CA SAE fur Ersatz (for replacement). Teile-Nr.61 21 8 381 762 neB (wet) ManUfaxtured for DETA-DOUGLAS BATTERIES, INC. by: DOULAS BATTEY Winston-Salem, NC 551072-1.eps 12 The Battery Battery Testing There are four steps to follow in testing an automotive battery: • Inspection • Removal of Surface Charge • State-of-Charge Test • Load Test Tools Needed To test a battery following tools are needed: • DVOM Digital Volt Ohm Meter • Battery Load Tester (i.e. Snap On VAT 60) • DISplus or MoDic • Battery Draw Test Special Tool PN 61 2 300 • Closed Circuit Measurement Adapter PN 90 88 6 612 310 • Temperature Compensating Hydrometer 5510112.jpeg 5510173.jpeg 6510199.jpeg 5510174.jpeg 13 The Battery Inspection Visual inspection is important for the detection of obvious problems: • Loose Generator Belt • Low Electrolyte Level • Corroded Cable or Terminal Clamps • Loose Hold-Down Camps or Cable Terminals • Damaged Battery Case Removal of Surface Charge If the battery has just been recharged, or the car has been driven, eliminate any surface charge by one of the following methods: • Allow the battery to sit for 2-3 hours. • Turn the headlights on high beam for 5 minutes and wait 5 minutes after turning off. • With battery load tester, apply a load of 1/2 the battery’s CCA for 15 seconds, then wait 5 minutes. State-of-Charge Test Use the table to determine the battery’s State-of-Charge. Pay special attention if the DVOM measurement of OCV is equal to: • 0 volts -Indicate an open cell. • 10.45 - 10.65 volts -Indicates a shorted cell. Note: The proper electrolyte level is just covering the plates, not all the way to the top of the battery inspection holes. Open Circuit Battery Voltage Approximate State Of Charge Average Cell SG 12.65 + 100% 1.265 + 12.45 12.24 12.06 11.89 75% 50% 25% 0% 1.225 1.190 1.155 1.120 5510173.eps 14 The Battery For non-sealed batteries, check both specific gravity (SG) in each cell with a temperature compensated hydrometer and battery OCV, without the engine running. For sealed batteries, measuring the battery’s OCV (without the engine running) with an accurate DVOM is the only way to determine the state-of-charge. Batteries with a built-in hydrometer measure the state-of-charge in one cell only. If the indi- cator is clear or light yellow, the battery has a low electrolyte level and should be refilled before proceeding or replaced. A state-of-charge reading BELOW 75% using SG, voltage measurement or dark indicator in batteries with built-in hydrometers, indicates the battery must be recharged before pro- ceeding. Replace the battery if one or more the the following conditions are met: • More than 0.050 difference in the specific gravity readings between the highest and lowest cell (There is a weak or dead cell). • The battery will not recharge to 75% or greater state-of-charge or the built in hydrometer does not indicate good (green indicates 65% or better). • DVOM reading indicates 0 volts (Open cell). • DVOM reading indicates 10.45 - 10.65 volts (Shorted cell). Load Test A battery which has a state-of-charge of 75% or greater or has a “good” built-in hydrometer indication may be load tested. With a battery load tester properly installed, load the battery for 15 seconds to one of the following: • One-half (1/2) the CCA (Cold Cranking Amps). • Three (3) times the AH Rating (Amp Hour Rating). The voltage on a good battery will NOT drop below 9.7 volts during the battery load test. After the load is removed, wait 5 minutes, the battery should bounce back to 50% or greater state-of-charge. If a battery drops below 9.7 volts during the load test, does not bounce back or fails to start the engine, the battery should be replaced. Batteries which pass this test should be recharged to restore peak performance. Load Test Conditions Tests assume electrolyte temperature of 800F, 26.70C. If the electrolyte temperature is above 80oF add .1 volt for every 10 degrees up to 1000. If the temperature is below 800F sub- tract .1volt for every 10 degrees to 40o. 15 The Battery Battery Maintainence Electrolyte Level If battery electrolyte level is allowed to drop substantially, the gas volume inside the battery grows proportionately resulting in an increased amount of flammable gas mixture. Any external or internal spark may result in an oxyhydrogen explosion. Additionally the plates are no longer covered by the electrolyte and may corrode. As described in SIB 61 01 90, battery electrolyte level should be checked on every Inspection I and Inspection II. Use only distilled water to top up the battery ! Tap water and electrolyte must never be used to refill or top off an automotive battery. Battery Cable Connections The top of the battery should be clean. Check for and correct corrosion on the top of the battery and the cable connections. Battery Charging The purpose of charging a battery is to put back the energy that has been removed. A battery that is not properly charged will deliver sub-standard performance and display a shorter life span. A battery should be charged only after performing a visual inspection on the battery case and the electrolyte levels. Never attempt to charge a battery with a damaged case or low electrolyte levels. A state-of-charge test should be performed before attempting to charge a battery. Always connect the positive lead of the battery charger to the positive terminal of the bat- tery and the negative lead of the battery charger to the negative terminal of the battery. Unplug the the charger or turn it off BEFORE disconnecting the leads at the battery. Workshop Hint Electrolyte levels may drop at a higher rate in the winter months, due to higher loads and increased utilization of electrical systems ( SIB 61 01 90). Workshop Hint Many battery problems are caused by loose or corroded connections. Insure that cables are free from corrosion and tight before continuing diagnosis. 16 The Battery Batteries that are fully discharged should be charged according to the following table. The best charging method is to SLOWLY recharge the battery using the BMW approved battery charger. . A slow charging rate allows more time for the electrolyte to penetrate the plates. Sulfated Batteries Continuous discharging of the battery or low electrolyte levels cause crystals to form on the plates. These crystals of lead sulphate occur when a battery is discharged. The deeper the discharge the more serious the sulphation. The sulphur molecules that form the sulphate are then absent from the electrolyte, causing the electrolyte to become inefficient. A battery relies on clean plates and strong electrolyte to both receive charging current and offer strong current discharge. A sulphated