C&DTECHNOLOGIES,INC.DYNASTYDivision900EastKeefeAvenueMilwaukee,WI53212Phone414-967-6500Fax414-961-6506Form41-2131(10/99)PrintedIntheU.S.A.TableofContents3345577899ChargerOutputACRippleVoltageandAffectonVRLABatteriesDCFloatVoltage,FloatCurrentandHeatingLeadAcidBatteryandDirectCurrentFlowACVoltageandCurrentConditionedACPowerforChargingandRippleVoltageRmsvs.P-PACVoltageandCurrentACRippleCurrentandBatteryHeatingACRippleVoltageandBatteryGassingACRippleVoltageandBatteryCyclingRecommendationsforOptimumServiceLifeListofFigures34556789Figure1-VRLABatteryFloatCurrentvs.VoltageFigure2-DirectCurrentFlowfromaBatteryFigure3-AlternatingCurrentFlowfromaGeneratorFigure4-120VAC(rms),60Hz(cps)WaveformFigure5-BatteryChargerRegulatedPowerSupplyFigure6-DCFloatVoltagewith0.9%P-PACRippleFigure7-ACRippleCurrentontheServiceLifeofaBatteryFigure8-ExtremeACRippleVoltageof9.9%P-PofVf2ChargerOutputACRippleVoltageandAffectonVRLABatteriesTheoperatingtemperatureis amajorfactorin thedeterminationofaVRLAbattery'sservicelife.Thebatterytemperatureisa functionofboththetemperatureoftheoperatingenvironmentandtheheatgeneratedwithinthebattery.Heatwillbegeneratedwithinthebatteryduetoexothermicelectrochemicalreactionswithinthecellsandcurrent,bothDCandAC,passingthroughtheresistivecomponentsofthecells(12RJ.DuringfloatchargingofthebatterywithapureDCvoltage(noACripple),thetotalenergyinputtothecellisexpressedinwattsandcalculatedasthefloatchargingvoltage(Vr}multipliedbythefloatchargingcurrent(Ir}.Forexample,ifafullychargedVRLAbatterywasaccepting0.2ampereswhilefloatchargedat13.8vdcitwouldbeconsuming2.76watts(Wattsdc=ViXlidc )fromthecharger.Theself-dischargerateoftheVRLAbatteryis verysmallandonlyabout2%ofthefloatcurrentwillbeconsumedinoffsettingtheself-dischargereactions.Undernormalconditions,another2%to3%is consumedin theoverchargegridcorrosionandgassingreactions.Thebulkofthefloatchargingcurrentorpower(upto96%)is consumedintheoxygenrecombinationcycle.Theoxygenrecombinationcycleisanexothermicreactionandit generatesheatinadditiontothatresultingfromthepassageofthefloatcurrentthroughtheresistivecomponentsofthebattery.Therefore,itis safetoassumethatupto95%ofthefloatchargingDCpoweris consumedanddissipatedasheat-sothewattsdissipatedasheatwouldbe:Wattsdc=VIXIldc X95%DCFloatVoltage,FloatCurrentandHeatingTheDCfloatcurrentis actuallyquitesmallandwillnaturallyvarywiththechargingvoltageasisshowninFigure1 .NotethatthefloatcurrentvarieswithnotonlythefloatvoltagebutalsowiththetypeofVRLAbatterytechnology(AGMvs.gel).Thisreflectsinlargepartthedifferencesintheefficienciesoftheoxygenrecombinationcycleofthetwotechnologies.Forexample,a100AhAGMVRLAbatterydraws200milli-amperes(0.2amperes)whenchargedat2.30voltsDCpercellwhilethegelVRLAequivalentbatterywillonlydraw100milli-amperes.Asaresult,theheatgeneratedbytheAGMbatterywillalsobegreater.Figure-VRLABattery Float Current vs. VoltageThe100AhcapacityAGMbattery,drawing0.2ampereswithachargingvoltageof13.8vdcwoulddevelopasamaximum,2.6watts(0.2amperesX13.8vdcX95%).Incontrastthe100AhgelVRLAbatterydrawing0.1amperescouldonlygenerate1.3watts(0.1AmperesX13.8X95%vdc)ofheat.HeatisgenerallyexpressedintermsofBritishThermalUnits(BTU's)whichistheamountofheatrequiredtoheatonepoundofwaterfrom59Fto6ifF.Onewattofheatwillgenerate3.4129BTU'sofheatperhour.Therefore;(AGM)2.6wattsX3.4129BTUperhour/watt=8.87BTUperhourper12voltbattery(Gel)1.3wattsX3.4129BTUperhour/watt=4.435BTUperhourper12voltbatteryLeadAcidBatteryandDirectCurrentFlowTheleadacidbatteryisanelectro-chemicaldevicethatproducesa constantpolarityandamplitudeofvoltageresultingina constantdirectflowofcurrent(DCordirectcurrent)inasingledirectionwhenappliedtoaresistiveload.~ iXed(Direct)VoltagePolarity+Figure2-DirectCurrentFlowfromaBatteryTheleadacidbatteryproducesaDCvoltageandcurrentondischargeasnotedinFigure2.Likewise,itrequiresaDCvoltageandcurrentforrecharging.However,theDCpowerrequiredforchargingisnormallygeneratedbyconvertingthecommercialACpowertoanacceptableformofDCpower.4~ IternatingVoltage-Polarity +~+Figure 3-Alternating Current Flow from a GeneratorACVoltageandCurrentThe.commercialACpoweris generatedelectro-mechanicallyin thewirewindingsoftherotatingarmatureofalargegenerator.Thiswillproduceanoutputvoltage,whichvariesinamplitudeandpolarityaboutaneutralpointasthegeneratorarmaturespins.Thefrequencyatwhichthepolaritychangesisa functionofthearmaturespeedofrotationandisusually50or60timespersecond.Thisisreferredtoas50or60cps(cyclespersecond)orHertz(Hz)power.Asaresultofthevoltagepolaritychanges,theresultingcurrentflowtoaloadwillalsochangedirectionandvaryinamplitudeatthesamefrequency-hencethenamealternatingcurrentorACFigure4-120VAG(rms),60Hz(cps)WaveformConditionedACPowerforChargingandRippleVoltageCommerciallyavailablepoweris ACandassuch,it mustberectifiedtopulsatingDC,regulatedtothecorrectamplitudeandfilteredwithcapacitorstoominimizeanyremainingAC,thusprovidingpureDCforchargingofVRLAbatteries.Thismaybedoneviaseveraldifferenttechniqueshowever,thatofFigure5illustratesa typicalapproach.Figure5-BatteryCharger/RegulatedPowerSupplyWhiletherectifyingdiodesconverttheACpowertopulsatingDC,thevoltageJegulatorwillclipthepeakstotheappropriatelevelforchargingofthebattery.Thefiltercapacitorwillthenstorepowerduringthepeakregulatedvoltageperiodtobereleasedduringthevalleysbetweencycles,thus"smoothing"theoutputandminimizingtheACripple.AsnotedinFigure5 theremaybea slightresidualACripplein theoutputvoltageofthechargingsystem.ThetotalheatdissipatedbythebatterywillbethesumofthatgeneratedduetotheDCfloatchargingcurrentandanyremainingACripplecurrentsuppliedbythechargerandflowingthroughthebattery.Thefrequencyoftheripplewillbea functionofthechargerdesignandwillhavelessimpactthehigherthefrequency.CloserexaminationofthisoutputwithanoscilloscopewouldrevealawaveformsimilartothatofFigure6.62.28..J2.26..JW2.24(,)~2.22Wc..2.2W"2.142.120 0.005 0.010.0150.02SECONDS0.025 0.030.035Figure6-DCFloatVoltagewith0.9%p-pACRippleIf thischargeroutput,havinganACripplevoltageof.020voltspeaktopeak(p-p)percellasshowninFigure6,isappliedtoa2 voltcellhavingaresistanceof0.001 ohms,anACripplecurrentof20amperesp-pwillflowthroughthecell(20amperesp-p= 0.020voltsp-p/0.001ohms)resultinginanadditionalheatingeffect.Rmsvs.p-pACVoltageandCurrentMosttestequipmentusedinmaintenanceofbatterysystemsreadswhatiscalledtherms(rootmeansquared)valueofthemeasuredvoltageandcurrentratherthanthepeaktopeak(p-p)values.The"rms"valueis thatACvaluewhichwilldotheequiliventworkofthesameDCvalue.Asanexample,10 amperesACrmswillgeneratethesameheatthrougharesistance,aswill10amperesDC.Therelationshipbetweenthermsvalueandthepeaktopeak(p-p)valueis:Yrms=0.707X(Yp-p/2)Forexample,the120voltsAC(rms)wemeasureatourelectricaloutletathomeis actually338voltspeaktopeak(p-p)asshowninFigure5andis calculatedas:120V rms =0.707X(338Vp-p/2)AC.RippleCurrentandBatteryHeatingIntheprecedingexample,the0.02voltsp-pripplevoltagepercellwouldbemeasuredas0.007Vrms percell.Thiswouldbe0.3%ofthepercellfloatvoltageof2.25vdc(0.007Vrms/2.25v/c).TheresultingACripplecurrentwouldbe7amperesrms(0.007Vrms /0.001ohms).Notethattheripplevoltageiswithinthetypicallyrecommendedmaximumof0.5%(rms)oftheDCfloatvoltage.However,theripplecurrentof7amperesrmsdoesexceedthenormallyrecommendedmaximumof5amperesrmsper100Ahratedcapacity.Thisripplecurrentof7ampereswillcreateheatingwithinthe6-ce11100Ahbatteryof0.294watts(12rmsRJ.Thisisinadditiontothe2.6wattscreated---~.--~...,ACRippleVoltageImposedontheDCChargingVoltageEqualsRe$ultingChargingVoltageIDCChargingVoltageperCeJICellOpenCircuitVoltage-~""'bytheelectro-chemicalfloatchargingreactionswithinthebatteryandtheIfdc2R;losses.Obviously,excessiveamountsofACripplecurrentcanhaveamajorimpactonbatteryinternalheatgenerationandservicelife.TheimpactofbatteryheatingduetoACripplecurrentontheservicelifeofa 31AhVRLAgelledbatteryisillustratedinFigure7.1.005-11.-40)(/)~30)~~m2~0)a.E10)1-00.95c00.90~mu..0.854)-::i0.800.75159 10 11 12 13 142 3 4 5 6 78ACAmps0 1LifeFraction PredictedTemp ActualT emp .~Figure7TheACripplecurrent(IAc)isdrivenbytheACripplevoltage(V AC) fromthechargerandwillbeafunctionofthecell(battery)internalresistance(RJinaccordancewithohmslaw,IAc=V Ac/R.Ascanbeseenin theequation,IAc=VAdA,theACripplecurrentwillincreasewithincreasingACripplevoltagefromthecharger.Also,notethattheACripplecurrentfora givenACripplevoltagewillvarywiththeinternalresistanceofthespecificbattery.Forexample,ahighrateAGMtypeofcellwitha verylowinternalresistancewillexperiencea greaterACripplecurrentthanthatexperiencedbyahigherresistancegelledelectrolytecellwiththesameappliedACripplevoltage.ACRippleVoltageandBatteryGassingBeyondtheconcernforheatingduetoexcessiveACripplecurrentthereis theadditionalconcernforbatterygassinganddryoutduetoexcessivechargingvoltages.ConsiderthattheVRLAbatterymaystarttogasatabout2.35v/c,andthatthemaximumrecommendedDCfloatvoltageis2.30v/c.It becomesobviousthattheripplevoltageshouldneverexceed+/-0.05v/c(0.1v/cp-p)or4.3%p-p(1.5%rms)ofthefloatvoltageorthepeakvoltagewouldbeabovethegassingvoltageandthiswillresultinelectrolyteprematuredryout.82.4w2.35(0?1--JO2.3>(/)~02.25wZ1-Z2.21-(/)~2.152.10 0.005 0.010.0150.020.025SECONDS(60CYCLES= 1 SECOND)0.03 0.035Figure8-ExtremeACRippleVoltageof9.9%p-pofVIACRippleVoltageandBatteryCyclingTheopencircuitvoltageoftheDynastyVRLAbatterywithSG=1.300is 2.14voltspercell.Obviouslythechargingvoltageshouldnotgobelowthisvalueortheload,whichisconnectedinparallelwiththechargerandbattery,willdischargethebatteryduringthatportionofthecycle.Witha floatvoltageof2.25vlc,theripplevoltagemustneverexceed+1- 0.11(0.22vp-p)or9.9%ofthefloatvoltage.Shouldthisoccurethebatterywillactuallybecycledattheripplefrequencyastheresultingchargingvoltageperiodicallydipstobelow2.14vdc(2.25vdc-0.11vdc).Again,thiswouldresultnotonlyinextremeheatingduetotheexcessiveACripplecurrentpassingthroughthebatterybutalsorapiddeteriorationoftheoftheplateactivematerialandgridduetocycling.RecommendationsforOptimumServicelifeBasedontheprecedingcommentsit isobviousthatideally,therewouldbenoACripplein theDCchargingvoltage.Realistically,thisisnotalwayspracticalfromaneconomicstandpointorevennecessary.However,toobtainoptimumservicefromtheDynastyVRLAbatterythefollowingrecommendationsshouldbeadheredtoo:TheACpoweredfloatchargerdesignshouldbesuchtominimizetheACripplecurrentthatwillbedrawnbythebatteryduringthefloatphaseofchargingtolessthan5amperesper100Ahofratedbatterycapacity.Thismaydemandthatoutputripplevoltagebelessthanthemaximumallowedduetothelowinternalresistanceofthespecifictypesofbatteriestobefloatcharged.12 Themaximumallowableripplevoltageduringthebulkphaseofchargingshouldbelimitedto1.5%rmsofthefloatvoltageandto0.5%ofthefloatvoltageduringthefloatphase.9Themaximumallowableripplevoltageduringthefloatphaseofchargingshouldbelimitedto0.5%ofthefloatvoltage.3.Themaximumallowableripplevoltageduringcycleservicechargingshouldbelimitedto1.5%rmsofthechargingvoltage.4.Whenperformingperiodicmaintenance,theACripplecurrentshouldbemeasuredtoassureitislessthantherecommendedmaximumof5 amperesrmsper100Ah.Ifthemeasuredvalueisincreasingfromtheoriginalvalueitmaybeanindicationthatthechargeroutputfiltersaredegradingandrequirereplacement.5.10