Thermoelectric Coolers Direct Performance Testing - TEC ...

Qmax is the max TEC cooling capacity - the level of heat a thermoelectric cooler can pump from the cold side to the heatsink. And here we should bear in mind ... Thermoelectriccoolersareusednowinmanyapplications.TherearefourkeyTECparametersyoumayfindinanyspecificationfromTECvendor:dTmax,Qmax,ImaxandUmax.Thefirsttwo-dTmaxandQmaxparameters-arethemostimportantforTEcooler-theyindicateTECperformancelevel.Secondtwo-ImaxandUmax-describetherequiredelectricalcurrentandvoltagetoreachthespecifieddTmaxorQmaxlevel.dTmaxisthemaxpossibletemperaturedifferencethatTEcoolercancreatebetweenitscoldandhotsidesatzeroheatload.It’sessentialtounderstandthatdTmaxisspecifiedwithoutheatloadappliedtoTEC.QmaxisthemaxTECcoolingcapacity-thelevelofheatathermoelectriccoolercanpumpfromthecoldsidetotheheatsink.AndhereweshouldbearinmindthatthermoelectriccoolerparameterQmaxisspecifiedatzero(!)temperaturedifferencebetweenTECcoldandhotsides(dT=0). Thuswegottwo“setpoints”-dTmaxatzeroheatloadandQmaxatzerodT-bothparametersfromtheTECdatasheetareconnected,andtheactualapplicationoperatingpoint(withaheatloadandrequireddTunderthisheatload)issomewhereinbetween.ThesetwokeyTECparameters(dTmaxandQmax)arethefirsttocheckwhenlookingforsuitableTEC.OnceobtainedfromtheTECdatasheet,theseparametersareacceptedastrustfulbydefault,preciselyastheTECmanufacturerspecified,nodoubtonthecustomerside.ButwherearetheseparametersinitiallytakenfrombyTECmanufacturers?Interestingly,theTECmanufacturerestimatedtheparametersdTmaxandQmaxusinginitialBi-TematerialpropertiesandFigure-of-Meritvalue.Thecriticalquestionisaboutverifyingtheseestimations,atwhatconditionstheyarespecifiedandhowclosetheestimationsaretoreality.Intherealworld,it’salwayspossibletofacespecificdifferencesbetweentheoreticalestimationsandactualresultsintherealworld.Inthecaseofthermoelectriccoolers,therearemanyfactorswithmoreorlessbeneficialinfluenceonactualTECperformanceafterassembly.AndtheestimatedTECperformancelevelmayhavecertaindifferencesfromactualTECparameters.Moreover,someTECmanufacturersmayapplythequitesimplifiedmathematicalmodelandestimationstocalculateTECperformanceparametersandpowerconsumption(andit'sclosetoactualvaluesas,say,carfuelconsumptionintheadvertbrochure-attractive,butlet'ssayfarfromreal).ThustheactualTECperformanceistobemeasuredbydirecttestingandcomparedwithinitiallyestimatedvalues.ThisishowithastobedonebyanexperiencedandreliableTECmanufacturer,bydefault.SuchproofrequiresadvancedR&DequipmentandhighexperienceinTECanalysistoexcludealldistortionsandtakeintoaccountallcorrectionsduringmeasurements.TherecanbesituationswhentheTECmanufacturerskipstheactualproofofTECperformancelevelandsimplyspecifiestheestimateddata.Andtherearealsocertaintrickstoattractcustomerattention-makingabithighervaluestodemonstratebetterperformance.Forexample,settingTECdTmax=75KinsteadofdTmax=72KlooksgoodintheTECdatasheet.Itcreatesagoodimpression,andonceit'sdTmax(specifiedatabsolutezeroheatload)-nobodyneedstheprecisionproofs.ThesameisabouttheQmaxparameter-it'sspecifiedatzerodT.Intherealapplication,thereisnoabsolutezerodT.ThuswhynotspecifyQmax=10Winsteadof9.5W?Itlooksbetter,shallwe?Thereisanothertrick-performancevaluesspecifiedathigherambienttemperature(specifiedusuallyasTamborThotinTECdatasheets):TECQmaxanddTmaxvaluesgrowwithambienttemperature.Thuslet'sspecifydTmaxandQmaxatambienthigherthancompetitorsandcreateaneye-catchingeffect.Whynot?It'sallaboutmakingagoodfirstimpression. Inmostcases,bigprojectsrequireseveralTECvendors,andtheinitialchoiceofvendorismadeundertheimpressionofinitiallyprovidedtechnicaldatasheetsandparametersestimations.ThesameTECsolution,withevenslightlyhigherperformance,looksbetter.Thussomeslight“advantages”inTECspecsgivecertainbenefitsfortheTECvendor(andtheprice,ofcourse).Usually,TECconsumerhasnoactualabilitytoprovetheexactTECmaxperformancelevel.TECconsumersimplyreliesondatasheetvaluesasspecified.TECmaxperformanceparametersarerequiredfortheinitialTECchoiceandveryroughanalysisonly.Theytechnicallycreateaninitialimpressionandstartnext-levelnegotiations,whileactualTECperformanceistobetestedlaterinrealapplicationconditions.Marketingtricksareusedforthethermoelectricindustry,sameasinmanyothers.TECkeyparametersinthedatasheetcanbespecifiedat,say,50ºCambient,whileothervendorscanrateitat27ºCbydefault-andtherewillbeavaluablevisualdifferenceintermsofdTmaxandQmax.ItwillbevaluableenoughtoattractcustomersattheinitialTECchoicestage.SomeTECmanufacturersgofarmoreandspecifyTECmaxperformanceparametersatmuchhigherambienttemperatures.Itlooksexcellentinthedatasheet,whiletheperformanceisthesame(orevenlower)asothervendorshaveiftospecifyitat27ºCambienttemperature.HINT:ThefirstthingtocheckwhenlookingatperformanceparametersinTECdatasheetistheambienttemperature,atwhichTECperformancedataisspecified.Inmostcases,it'snotedas"Tamb","Thot"or"Th"inthedatasheet("Thot"and"Th"meansthetemperatureofTEChotside,whichisacceptedequaltoambienttemperatureinoptimalconditions).Whenit'snotspecified,it'sessentialtoasktheTECmanufacturertoavoidanymisunderstanding.MostTECvendorsspecifyTECperformancedataat+27ºCand+50ºC.Example-fragmentfromTECDatasheet(Japan)ThenextcriticalmomentfortheTECperformancedatasheetstudyistheambientconditions-gasorvacuum.TECdemonstratesthebestperformanceinavacuum,withoutapassiveconvectionalheatloadfromthegasambience.Inthecaseofagas-filledatmosphere,itsconvectionalheatloadhasaparticulareffectonTECparameters,directlyproportionaltoTECsize.ThelargertheTECsizeis,themoreeffectfromconvectionalheatload.TraditionallyTECvendorsspecifyperformanceparametersat+27ºCinavacuumand+50ºCinDryAirorDryNitrogen.ThishistoricallycomesfromtypicalTECapplications:X-RayorIR-detectorsinvacuum-sealedpackagesoperatinginnearroomconditions,andtypicallaser(LD)applicationswithoperatingtemperaturescloserto50ºC,withgas-filledcontrolledambiance.Andifforthecaseofsingle-stageTEcoolers,thereisnosignificantdifferenceinmaxperformanceinvacuumorgas-filledatmosphereforsingle-stageTEcoolers,whilemulti-stageTECsareprettymuchsensitiveforsuchthings. InthecaseofprofessionalsupportfromtheTECvendor,alltheestimationsaboutTEC'sTEC'sactualpowerconsumptionintheoperatingmodecanbeprovided.Theactualtestingresultsinoperatingmodehavetomatchtheestimations,ideally.Butitistherealworld,andtheactualresultsmaydifferfromtheestimations.AllthesemayleadtocertaindebatesbetweenTECsuppliersandTECconsumers.Hereisaprettytypicalsituation:TECconsumerspecifiesapplicationrequirements(intermsofTECsize,operatingconditions,heatloadlevelandrequireddT),TECvendorsuggestsoptimalTECsolutionandprovidesnecessaryestimations;consumerinstallsTECandobserveshigherpowerconsumptionthanestimatedbyTECvendor,orlowerTECperformancelevel.TECvendorisprettysureaboutestimatedvalues.TECconsumerisprettymuchsureaboutthedesignandspecifiedapplicationconditions.Whereistheproblem?Therecanbevariousreasonsforthat.Incorrectlyestimatedapplicationconditions:higherambienttemperature;overheatingduetoimproperheatsinkorpoorthermalcontact;excessiveheatloadtoTEC;ambientinfluence(unexpectedconvectionalandradiationalpassiveheatload),etc.Also,itispossibletogetTECperformancedropbecauseofspecificimpactsordamagesduringthedeviceassembly/TECintegratingstage.Orthecompellingcase-actualTECperformancemayhaveaparticulardeviationfromdatasheetvaluesorTECmanufacturerestimationsbecauseofaninsufficientorsimplifiedmathematicalmodelinestimations.Thus,thereshouldbeareliableTECperformanceverificationandapprovalmechanism-alaboratorytestingsystemwhereyoucanmakeactualTECapplicationoperatingconditionsandapplyapreciselycontrolledheatloadtotestTEC'sactualperformanceleveldirectly,inpraxis.Oncesuchaverificationapproachisimplemented(realized),itiseasytoanalyzetheresultsandgetthereal,verifiedTECperformancelevel.Thenitispossibletoanalyzethereasonsforobtaineddeviationswiththeoreticalestimations-ifit'saboutunexpectedapplicationconditionslikeoverheatingorexcessiveheatload,oractualdeviationofTECrealperformancevaluesfromtheestimatedvalues.TECMicrosystemsGmbH,withalreadytenyearsofexperienceinthermoelectriccoolersanalysis,developmentandmanufacturingsetup,offerstheuniqueservice-directtestingofTECperformanceandpowerconsumption.AllTECperformanceparameterscanbeanalyzedandmeasureddirectly.TheanalysisismadewithaspeciallydevelopedprofessionalTECtestingsystem-DX8020TECExpert(availablealsoforordering).DX8020combinesdirectTECperformanceparameterstestingandmeasuringparametersofthermoelectricsingle-stageandmultistagemodules.ThetestingprocesswithDX8020allowscheckingthefollowingparameters: DIRECTTECPARAMETERSTESTING MeasuredParameter  Designation  TEmoduletemperaturedifferenceversuselectriccurrentatzeroheatload  ∆T=f(I)  TEmodulemaximumtemperaturedifferenceatzeroheatload  ∆Tmax  Electriccurrentatwhich∆Tmaxisachieved  Imax  TEmoduleelectricvoltageversuselectriccurrentatzeroheatload  U=f(I)  Electricvoltageatwhich∆Tmaxisachieved  Umax  TEmoduletemperaturedifferenceversusheatloadavailableatelectriccurrentfixed(loadedplots) Q=f(∆T)  MaximumheatloadcapacityatImax(∆T=0)  Qmax  ActualTECPowerconsumptionunderspecifiedheatloadQ0 P ActualTEC∆Tlevelunderspecifiedconditions(ambience/heatload) ∆T TEmoduleFigure-of-Merit  Z  TEmoduleelectricresistance  R  TEmoduletimeconstantat0.01Imax  τ  AverageSeebeckcoefficientofTEmaterial  α  AverageelectricconductivityofTEmaterial  σ  TECtestingwithDX8020providestheautomaticcapabilitytomeasurethefullspecificationsofaTEmoduleatonemeasuringcycleingivenambientconditions.It’sintendedforacceptance,qualificationandresearchtestingofTEcoolers.Thedirectanalysisismadeonananonymousbasis.TECvendornamesarenotrequiredfortesting.TECMicrosystemslaboratoryanalyzesona“SampleA,SampleB”basis.TherearethreetypesofdirectTECtestingservicesprovidedbyTECMicrosystems:     1.     Standardtests,simpleTECverification-directtestingofactualTECperformancelevel(maxparameters),comparisonwithTECvendorestimations/datasheetvalues.     2.     Expertmodetests-detailedTECanalysiswithdirectperformanceandpowerconsumptiontestinginoperatingconditionsspecifiedbythecustomer.     3.     AdvancedcomparisonanalysisofmultipleTECs,optimalsolutionfinding-directtestingofseveralprovidedsamplestofindthemostoptimalone,comparisonoftheperformancelevelandpowerconsumptionatspecifiedoperatingconditions.ExpertmodeandadvancedcomparisontestingalsoincludeTECmaterialandperformanceanalysis-directmeasurementofpelletsmaterialElectricalconductivityandSeebeckcoefficient.TECMicrosystemsdirectTECtestingservicessavetimeandbudgetforTECconsumers,solvethedisputablesituationsaboutdifferenttestingresultsandhelptounderstandtheactualTECperformancelevel.Professionalanalysiswithhigh-endlaboratoryequipmentsimplifiesoptimalTECsearchandgivespreciseandaccurateresultsaboutactualTECperformancelevelandpowerconsumption.SEND  REQUESTHerearesomeexamplesofdirectTECtestingstories:Story#1:Customerobservessignificantlyhigherpowerconsumptioninapplicationconditions,differenttoestimationsinitiallymadebyTECvendor.DirectTECtestinginthelaboratoryprovedthecorrectestimationsofTECvendor,estimatedvaluesmatcheddirecttestingresults.Followingthedetailedanalysisofcustomerapplicationanddesignrevealedsignificantpassiveheatloadlevel,nottakenintoaccount.Problemsolved.Story#2:CustomerobserveslowerperformancelevelofTECinactualapplicationconditions,haddoubtsinTECparametersspecifiedbythevendor.DirectTECtestingwasorderedas3-rdpartyexpertise.Laboratoryprovedtheproblem.CustomerdesignhadnomistakesdespitetheTECvendorstatement.TheactualTECperformancelevelwasfound~15%lowerthanexpected.ThecustomerswitchedtoareliableTECvendor.Story#3:CustomerclaimedhigherTECpowerconsumption,muchhigherthanexpectedfromestimationsprovidedbyTECvendor.DirectTECtestingintheTECMicrosystemslaboratoryprovedtheperformancelevelofTEC.Thedetailedanalysisofcustomerdesignrevealeda2-wiresmeasurementschemeforTECvoltageandseverevoltagedroponheaderpinsconnectedtoTEC.Problemsolved.Story#4:ScientificcenterordereddetailedTECperformanceanalysisinvacuumconditionsandpossiblerisksofperformancedropincaseofleakageandgas-filledambiance.Researchmade,optimalTECsolutionwithcoolingcapacityreservewasfoundandapproved.Story#5:Customerordereddetailedcomparisonanalysisofthermoelectriccoolersmadebybulkandthin-filmtechnologyinvariousapplicationconditions.SignificantadvantagesofbulkTECtechnologywereconfirmedinspecifiedapplicationconditions.Story#6:TECvendorappliedchangesintechnologywithrelatedPCNtocustomer.TECparametersremainthesame,butthecustomerobservesspecificperformancedifferenceswiththenewsolutionandinitiatesanRMAdiscussionwiththeTECvendor.DirectTEC'stestingwasorderedandusedas3-rdpartyexpertise.DirectTECtestingrevealedmoderatechangesintheupdatedTECsolution.Bothsidesagreed,theproblemwassolved. 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