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62SEPA EUROPE
7 tips for buying a fan
Keepingacoolheadinselectingtherightone
Thedeveloperofelectronicdevicesandequipmentisnow, (burnt-in),whichmakesearlyfailuresunlikely.Fanswithsolid
morethanafewyearsago,confrontedwiththedifficulttask bearingsare notsuitableforawidetemperaturerange,despiteall
ofheatdissipation.Althoughmanycomponentsproduce theimprovementswithsinterbearingtechnology.Claimsaremade
significantlylessheatduetotechnologicalimprovements,the thatfanswithsolidbearingsaremoreresistanttoshock.However,
devices’powerhasrisenbyalmostthesameextent.The andespeciallyathightemperaturestheyarelikelytowearout
componentdensityhasespeciallyincreased,whichmakes morequickly–eveniftheadvertisingpromisessomething
effectiveandprecisecoolingmoredifficult.Carefulcooling- different.
managementforcomponentsismoreimportantthaneverbefore.
Youcanexpectgoodcoolingresultsifcertainaspectsare
observedwhenbuyingfans. 4
Alwaysusethelargestpossiblefantominimisenoiselevel.
Whereappropriate,chooseareducedspeedoruse
1
temperaturetocontrolthespeedofthefan.
Dimensionthecoolinggenerously.Itisalwayspossibleto
simplifyanelaboratecoolingarrangement,butunder
capacitycoolingrarelysucceeds.Thecapacitysometimes 5
Ninetyninepercentoffandefects,especiallywithsmall
fans,arecausedbyin-correcthandling.Never
specifiedinthefandatasheetsisforanairflowwithoutback- touchtherotor,certainlydonotdistortit.Fansshould notbe
pressure.Here,thedatadepictsthemaximumairflow.However,if stackedinstore.
thefanblowsinaclosedspace(withoutairleakage),itproduces
maximumpressureatzeroairflow.Thischaracteristicisalso
showninthedatasheets. 6
Themountingofthefanframeisimportant.Typicallyhigh-
qualityplasticisused.Nevertheless,itispossibledueto
incorrect,toohighortoolow,processingtemperatures,during
pressuremouldingtogetbarelydiscernablefaults.Suchfansare
0
8 2
Don’tbeafraidofactivecooling!Theterm"fan-less"inthe
equipmentdescriptionisoftenconfusedwithmaximum easilydeformedbyhandandcanchangedimensionallyduring
reliability.Theelectromechanicalfanitemisoftenclassifiedasa operationsothatthefanbladestouch.Fansfromother,partially
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riskcomponent.However,afan-lessdesignisoftenboughtwith transparentplasticsarenotrecommended.Tomakesurethatthe
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manydisadvantagesandmoreriskthanadesignthatcontains fanframeisnotdistorted,theassemblymustalwaysbeattached
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fan.Thewidespreadpoorqualityoflowcostfansleadstoahigh toaflatsurface.
probabilityoffailure.Thisrisksthecooleddeviceswith
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correspondinglyhighcostsfortherepairandfortheresulting
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consequences.Asaresult,attemptsaremadetoreducetherisk 7
WhereDCvoltageisnotavailableACfansareused.These
fansareveryexpensiveandrequireadisproportionate
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ofproblemsbyusingdesignswithoutafan.Whatisoverlookedis amountofunusedpowerbecauseoftheregulationsandinsulation
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thatthelowreliabilityofthefansresultsfromtheverylowprice ofthecoils.ACfanswithintegratedAC/DCconvertershaveagood
thatsomesuppliersusetogainacompetitiveadvantage.It efficiency,buttheyarealsoexpensiveandrequireadditionalspace
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C
invariablyfollowsthatinadequatecoolingoftemperature severalcentimetresdeep.Moreover,thevarietyoftypesislimited.
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sensitivedevicesresultsinincreasedriskofdramaticdamageto ItispreferabletouseanexternalAC/DCconverterthatcansupplya
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componentssuchaselectrolyticcapacitors. standardDCfan.Thereisinvariablyalittlespaceleftsomewherein
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thedeviceforsmallconverters.Ifastandardfancanbeused,there
Cheapfansareexpensivetouse.Somefailureswithserious aremanyoptions,evenforsmallandmedium-sizedquantities.
consequencescouldhavebeenavoidedbytheuseofgood
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qualityfanswithballbearings.Also,goodfansarepre-aged >www.sepa-europe.com
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