汽车电器设备（英文版）1蓄电池

《Automotive Electrical Equipment》 Wuhan University of Technology Chen Bifeng Introduction: 1. Basic component parts of vehicle electrical equipment (1) Power sources: include battery,alternator with regulator. (2) Ignition system: includes conventional(or contact-point)ignition system or electronic ignition system. (3) Electric consumers: include starting motor,lighting and signal system, instrument and warning equipments and other accessory electrical equipments. (4) Electronic control equipments: include electronic fuel injection(EFI),electronically controlled Anti-lock brake system(ABS), electronically controlled automatic transmission. (5) Power distribution equipments:include switches,fues,cables and wires,etc. 2. Characteristics of vehicle electrical system (1) Double power sources(battery and alternator). (2) Low-voltage and direct current(DC 6v,12v,24v). (3) Parallel electric circuit and one-wire system. Series electric circuit Parallel electric circuit (4) Negative grounded. Electric consumer Fuse switch Battery Earth (vehicle chassis or body) Chapter 1 The automotive battery(lead-acid) 1. Functions of battery (1) Supply current for starting motor and ignition system when starting engine (2) Assist the alternator to supply current when the alternator is not handling the load. (3) Transform one form of energy into another,or electric energy chemical energy. (4) Protect the electric circuit when overvoltage produced.The battery seems to be a big capacitor(or condenser). 2. Battery construction There are 6 cells for a 12V battery(or 3 cells for 6V battery)in series-connection. One cell has 2 volts theorectically.Then,a battery has 12 volts(2volt×6=12 volts). Components: (1) Electrode plates: Positive plates: active material is lead peroxide (PbO2)and the colour is deep brown. Negative plates: active material is pure lead(Pb)and colour is grey. Generally negative plates have one more than positive plates. All active materials are held in the plate grids. (2) Separators :they are porous materials of wooden sheets,spun glass,spong-rubber sheets. (3) Electrolyte:it consists of sulfuric acid and distilled water. Specific gravity is about 1.24~1.30g/cm3 according to the battery status. (4) Case: made from hard rubber,or modacrylic plastic. (5) Connectors (internal):they connect positive plates and negative plates. (6) Terminals:include positive terminal and negative terminal.Generally ,the positive terminal is larger than the negative terminal. (7) Vent caps(or filler plugs):to add electrolyte and ventilate. (others include cell partition,element rest,sediment space,one-piece cover) 3. Battery model number The model number is composed of four portions. 6cells or 3cells Q-for starting A-dry charged type expressed in Ah H-wet charged type W-maintenance-free type Note: some special properties can be added after. G means high starting power; D is used for low temperature. For example: 3-Q-90: 3cells, rating voltage is 6 volts,rating capacity is 90Ah 6-Q-105: 6cells, rating voltage is 12 volts, rating capacity is 105Ah 6-QAW-100: 6cells, rating voltage is 12 volts,dry charged and maintenance-free type, rating capacity is 100Ah 4. Operating principle(or chemical reaction)in battery As mentioned above, active material of positive plate is PbO2 , active material of negative plate is Pb, electrolyte is H2SO4(about 35%)and H2O(about 65%). Chemical reactions on positive and negative plates: Positive plates’ chemical equation is as following: recharge PbSO4-2e+2H2O+SO42- PbO2+2H2SO4 discharge Negative plates’ chemical equation is as following: recharge PbSO4+2e+2H+ Pb+H2SO4 discharge General chemical equation of battery: discharge PbO2+ Pb+2H2SO4 2PbSO4+2H2O recharge When discharging, the specific gravity decreases. When recharging, the specific gravity increases. The chemical reactions that take place are rather complicated.The sponge lead(on negative plates)and lead peroxide(on positive plates)change to lead sulfate during the discharge process.The sulfate comes from the sulfuric acid.The electrolyte loses acid and gains water as sulfate goes into the plates.Therefore,discharing the battery changes the two different chemicals in the battery plates to a third chemical,lead sulfate. Recharging the battery changes the lead sulfate back to sponge lead in the negative plates,and to lead peroxide in the positive plates. Meanwhile,the sulfuric acid reappears in the electrolyte of the battery. 5. Operating characteristics of battery 5.1 Battery electromotive force,internal resistance,and terminal voltage 5.1.1 Single cell’s static electromotive force E0=0.84+ρ25℃ E0- static electromotive force ρ25℃- relative specific gravity(or density)at 25℃ For different temperature,specific gravity should be converted into the standard. Conversion formula of variations of specific gravity: ρ25℃=ρt+β(t – 25) ρ25℃—standard specific gravity ρt—actually measured specific gravity β—temperature coefficient,0.00075 t—actually measured temperature e.g. 1.250 g/cm3(at 48.9℃) 1.268 g/cm3(at 25℃) 1.280 g/cm3(at-1.7℃) 1.260 g/cm3(at 25℃) In other words: ρt =ρ25℃ -β(t – 25) t↗, ρ↘; t↘, ρ↗ 5.1.2 Internal resistance(R0) Internal resistance is the summation of resistances of electrode plates,separators,electrolyte, connectors,terminal posts.Generally it is very small(about 0.011Ω),and sufficient for starting the engine.For a fully charged battery,R0 at 20℃can be calculated by the following empirical formula: Ue— rating voltage (V)of battery C20 — rating capacity(Ah)of battery Characteristics: (1) Electrode plate resistance decreases after battery recharged and increases after discharged because of PbSO4 produced. (2) Separator resistance: Usually the resistance of wood material is greater. (3) Electrolyte resistance(R1):It varies with temperature (t) and specific gravity (ρ).Lower the temperature,higher the resistance,and R1 is the minimum at 1.2g/cm3(15℃) because of the easy dissociation of electrolyte. 5.1.3 Terminal voltage (U):When discharging,terminal voltage is less than electromotive force, Relation formula is U=E-IfR0; When charging,terminal voltage is greater than electromotive force, Relation formula is U=E+IfR0 5.2 Discharging characteristics of battery 5.2.1 Definition: Discharging characteristics describe the variation regularity of terminal voltage(U), electromotive force (E0) ,specific gravity(ρ) with the discharging time(tf) during discharging battery at constant current. U 2.1V E0 1.95V Uf ρ25℃=1.29 1.75V ρ25℃=1.1 If=5.25A C=If*tf=105Ah 20 tf(h) Discharging characteristics of battery 5.2.2 Termination characteristics of discharging (1) Single cell’s voltage decreases to 1.75V(at 20h) (2) Specific gravity decreases to 1.10g/cm3 Note:excessive discharging will damage electrode plates and reduce battery capacity. 5.3 Charging characteristics of battery 5.3.1 Definition: Charging characteristics describe the variation regularity of terminal voltage(U), electromotive force (E0) ,specific gravity(ρ) with the charging time(tc) during charging battery at constant current. termination of charging 2.4V 2.7V rest U Uc E0 2.1V 2.1V 1.95V ρ25℃=1.29 ρ25℃=1.1 Ic=10.5A overcharging C=Ic*Tc=105Ah 10 11 tc(h) Charging characteristics of battery 5.3.2 Termination characteristics of charging (1) Large amount of air bubbles occur and present a boiling phenomenon. (2)Terminal voltage reaches maximum and stops increasing within 2 hours. (3) Specific gravity reaches maximum and stops increasing within 2 hours. 6. Battery capacity Battery capacity is the ability in Ampere-hours(Ah) of a fully-charged battery to deliver current under the specified conditions. C=Ift C—Battery capacity If—Discharge current t—Discharge time Battery capacity is related to the discharge current, discharging end-point voltage and the temperature of electrolyte. The national standard stipulates that Ampere-hour capacity (or 20h capacity) is designated as the battery rating capacity. Classification of battery capacity: Ampere-hour capacity (or 20h capacity or rating capacity) Reserve capacity 6.1 Ampere-hour capacity (or C20) Ampere-hour capacity is the capacity which a fully-charged battery can supply for 20 hours at a specified discharge current (one-twentieth of the nominal quoted capacity) before the end-point voltage of 1.75v per cell is reached. The temperature of the electrolyte must be 25℃. For example,a battery that can deliver a current of 5A for 20 hours at 25℃ is rated as having a 100 Ah capacity(5×20=100Ah). For example,6-Q-105: at25℃,5.25A,20hs’discharging,and cell voltage dropping above 1.75V , then,C20=5.25×20=105 (Ah) 6.2 Reserve capacity(Cm) Reserve capacity is the length of time in minutes that a fully charged battery at 25＋2℃can deliver 25A without the cell voltage dropping below 1.75v. This figure tells how long a battery can carry the electric operating load if the alternator quits. A typical capacity would be 75 minutes for some battery. Conversion relation between Ampere-Hour capacity and Reserve capacity: C20－Ampere-Hour capacity,Ah Cm－Reserve capacity,min When Cm≥480min or C20>200Ah,the conversion relation is not suitable. Factors that influence battery capacity include the number of plates per cell,the size and thickness of the plates,the cell size,and the quantity of electrolyte,etc. 7. Battery charging 7.1 Battery slow charging Two methods of slow charging batteries are in use, the constant-current and the constant-voltage methods.In the constant-current method,the current input to the battery is adjusted to the manufacture’s specifications.The charging is continued until the battery is gassing freely and there is no rise in specific gravity for 2 hours. In the constant-voltage method,the charging voltage is held at a constant value(6V battery→7.4+ 0.05V, 12V battery→14.8+ 0.05V). The battery ,as it approaches a charged condition, increase in resistance to the charging current.At the same time , the current input gradually tapers off. When the battery is fully charged , the current input has been reduced to a few amperes.The battery electrolyte temperature must remain within limits.If the battery electrolyte temperature increases greatly,the resistanse of the battery will remain low. Then the battery will be damaged by overcharging,unless it is quickly removed from the charger. Before charging a battery,check the electrolyte level.If the level is low,the battery can be damaged.If the level is too high,the electrolyte can overflow because of gassing and heat.Here are cautions to observe: (1) The gases released by batteries under charge are very explosive.Be sure the area is well ventilated.Do not smoke or have open flames around charging batteries.This could cause an explosion. (2) Be sure to disconnect the battery ground strap if the battery being charged is in a car.Otherwise,you can damage the electrical equipment in the car. (3) Most manufacturers recommend leaving the cell caps in place.But make sure the vent holes are open.Cover the caps with a cloth during the charging procedure.Some manufacturers recommend removing the caps and covering the openings with a cloth. (4) Do not charge a battery that is frozen.It could explode. (5) Always wear some type of eye protection(goggles). (6) If the charge indicator of a maintenance-free battery shows yellow or clear,do not charge it.The electrolyte level is low,and charging it could cause an explosion.The battery should be discarded. (7) Do not turn the charger on until the charger cables are connected to the battery.Turn the charger off before disconnecting the cables. (8) Check the specific gravity and temperature of the electrolyte periodically during charge.If the temperature goes above 51.7℃(125℉),stop the charge. (9) The battery is fully charged when the specific gravity shows no increase for2~3 hours.Also,the cells should be gassing freely. (10) After charging,wash and dry the battery top.This removes any electrolyte that might have spewed out during charge. 7.2 Quick charger The quick charger can be wheeled up to the car and connected to the battery in the car. Here are some special points to watch when using a quick charger.These chargers can supply a fast charge up to 100 amperes(0.8~1C20) for some types. Normally,you would set the charging rate for about 40 to 50 amperes and charge the battery for about 30 to 45 minutes.This boosts the battery with up to 38 ampere-hours of charge.A battery in normal condition can stand high charging rates without damage if the electrolyte temperature does not go above 51.7℃(125℉). Quick charging usually cannot bring the battery up to full charge in a short time.To bring it up to full charge,the battery should be given a slow charge after the quick charge. A very low battery may not accept a fast charge.The electrolyte in a very low battery does not have very much sulfuric acid in it.Therefore,the conductivity of the electrolyte is too low to allow a high current to flow through the battery.You might think a battery that refuses to take a high charge is worn out.However,it may be possible to restore the battery to a charged condition.First,slow charge it for a few minutes to see whether it starts coming up to charge.If it does,then it can be put on fast charge. 8.Battery troubles, possible causes and corrections (1) Sulfation If the battery stands for a long period in a discharged condition,the lead sulfate is converted into hard,crystalline substance and is difficult to reconvert into active materials by normal charging processes.Such a battery should be charged at half the normal rate for 60 to 100 hours.Even though this long charging period may reconvert the sulfate to active material,the battery may still remain in a damaged condition.The crystalline sulfate,as it forms,tends to break the plate grids. Main causes: · Left unused for a long period · Electrolyte level is too low,active materials are oxidized · Electrolyte is impure and specific gravity is excessively high. PbSO4 is difficult to resolve. · Outside temperature varies greatly and accelerate recrystalization of PbSO4 Precautions: · Charge battery in a good condition · Check the electrolyte level regularly · Select proper specific gravity according to different seasons and areas · Care of battery in stock properly and it should be recharged every 30 days (2) Self-discharging It results from: · Impurity in the electrolyte · Dirty outside · Being left unused for a long period · Active material breaking off Correction: Clean battery; discharge completely and then,change electrolyte,recharge it. (3) Electrode plates shorted Main causes: · Separator damaged · Warped electrode plates · Excessive sediment of active material Correction: Disassemble and repair or discard. Other troubles: overcharging,undercharging,cracked case,bulged case,corroded terminals and cable clamps,corroded battery holder,dirty battery top. 9.Battery maintenance Complete baterry maintenance includes the following: (1) Visually check the battery(e.g. leakage,crack,corrosion,missing vent caps.) (2) Check electrolyte level and add distilled water if necessary. (3) Clean corrosion off battery. The corrosion of the terminals and cable clamps can be cleaned off with special wire brush.Top corrosion can be cleaned off by brushing the top with baking-soda solution and then flush it with water. (4) Check battery condition through hydrometer and battery discharge tester. 9.1 Checking electrolyte level Electrolyte level should be checked every 1000 km or 10~15 days in winter or 5~6 days in summer. Procedures: (for non-transparent case) (1) Remove all the vent caps of battery. (2) Insert a glass tube with a diameter of 5~6 mm into a cell. (3) Hand-press the open end of the top of glass tube and lift it vertically. (4) Read the level height at eye level .Properly it is 10~15 mm above the top of electrode plates. (5) If the level is low,add some distilled water. (6) One by one check the other cells. Note: If the battery case is clear,you can observe the level directly from the outside of battery. 9.2 Hydrometer test The hydrometer is used to test the specific gravity of battery electrolyte. There are two types of hydrometer: ball-type and float-type 9.2.1 Ball-type Ball-type uses a series of plastic balls.To use a Ball-type hydrometer,stick the rubber tube in the electrolyte.Then squeeze and release the rubber bulb.This draws electrolyte up into the glass tube.The number of balls that float tells you the battery state of charge.If all balls float,the cell is fully charged.If none float,the cell is discharged. 9.2.2 Float-type The float-type hydrometer has a float with a stem that sticks up above the electrolyte level in the tube.The float stem is marked to indicate the specific gravity of the electrolyte(a charged cell is between 1.25~1.30).The height of the stem above the eletrolyte tells you the battery state of charge.Here is what the readings mean: Readings (ρ25℃) Conclusions 1.265~1.299 fully charged battery 1.235~1.265 three-fourths charged 1.205~1.235 one-half charged 1.170~1.205 one-fourth charged 1.140~1.170 barely operative 1.110~1.140 completely discharged Note: · Reading must be taken at eye level. · A temperature error correction must be applied to this reading as mentioned above. ρ25℃=ρt+β(t – 25) For example: Given: t=50℃, ρt=1.265g/cm3 . Calculate: ρ25℃ Solution: ρ25℃=ρt+β(t – 25)=1.265+0.00075(50-25)=1.284 (g/cm3) 9.3 Battery discharge tester(6/12 volt heavy-duty) 1 2 R G G 3 4 Battery discharge tester Meter face 1—terminal tip 2—shunt resistance G—Green Band R—Red Band 3—meter 4—handle Before use,remove all vent plugs. Do not test immediately after charging.Test small battery (20Ah)for about 8 seconds and large battery up to 120Ah to 15 seconds.Wait 90 seconds between tests to allow tester to cool. To get reading,touch terminal tips with battery terminals and hold it within specified time.Here is what the readings mean: Meter readings Conclusion and recommendations Registers and remains steady in Green Band Battery healthy and charged Registers in Green Band then drops quickly into Red Band Battery healthy but discharged, recharge battery Registers in Green Band then drops quickly into Red Band and cell gases freely Battery has faulty cell, replace battery Registers low or zero. No gassing but sometimes make a fizzing sound Battery sulphated or internal open circuit(run down or dead battery),replace battery 9.4 Compound(make up)battery electrolyte Procedures: (1) Add sulfuric acid into distilled water slowly. (2) Meanwhile stir the mixture with wood stick or glass stick. (3) After the temperature drops below 30℃,check and adjust the specific gravity.Pour it into the battery.Statically keep it more than 4 hours. (4) Adjust the level ,15 mm above the electrolyte plates. (5) Charge battery. Proportion of water and acid 15℃specific gravity(g/cm3) Weight(%) Volume(%) Distilled water Thick acid Distilled water Thick acid 1.24 68.0 32.0 78.4 21.6 1.25 66.8 33.2 77.4 22.6 1.26 65.6 34.4 76.4 23.6 1.27 64.4 35.6 75.4 24.6 1.28 63.2 36.8 74.4 25.6 1.29 62.0 38.0 73.4 26.6 Selection of specific gravity at different temperature Lowest temperature of the applied area Winter(g/cm3) Summer(g/cm3) ＜- 40℃ 1.31 1.27 -30℃－ -40℃ 1.29 1.26 -20℃－ -30℃ 1.28 1.25 0℃－ -20℃ 1.27 1.24 10.New-type batteries 10.1 Dry-charged batteries Dry-charged batteries contain fully charged positive and negative plates but no electrolyte. The batteries are sealed with rubber or plastic seals placed in the vent plugs.Since they contain no moisture,practically no chemical action can take place in them.This means that they will remain in good condition for as long as 36 months. Add ready-mixed electrolyte supplied by manufacturers.Keep it still about 30 minutes,then it can be used. 10.2 Maintenance-free batteries(MF) This type of battery can be used for more than 3 years without any distilled water added because of its special construction. It is very convenient for vehicle drivers. Many maintenance-free batteries have a charge indicator on their top. The appearance of the charge indicator shows the state of charge of the battery. Battery top A: Green dot B: All dark C: All light A: If the green dot shows, the battery is charged. B: If the indicator shows black, the battery is low and should be charged before testing. C: If the indicator shows light yellow,the battery is dead and should be discarded. Characteristics Rating capacity Number of cells Purpose Page 11 of 11 _1185144348.unknown _1185309549.unknown