Technical_Information-Current-sharing

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1、SchunkKohlenstofftechnikTechnicalInformationCurrentsharingCurrentdistributionisoneofthemainbrushfeaturesinpracticalapplicationsandforOEMsaswell,sinceithasgotabiginfluenceg.onmaintenanceofelectricaldrives.A100%uniformcurrentdistributiondoesnotexist.Parallelbrushesineachset

2、alwaystrans-ferslightlydifferentcurrents.Abrush,whichinacertainobservationmomenthastransferredlesscurrent,mightbeflownthroughbymorecurrentatalaterstageandviceversa.Anexplanationforthisphenomenoniseasytobegiven,ifonetakesthevoltagedrop/cur-rentdensitycurvesintoconsideratio

3、n,whicharealsogiveninourdatasheets.Firstashortexplanationoftheusedterms:Thesumoftheresistancebetweenbrushcontactsurfaceandring-/collectorsurfaceiscalledcontactresistance.Thesumofthisvalueplustheresistanceofthebrushbodyandthearmatureiscalledthecontactresistanceofacarbonsli

4、d-ingcontact.Thevoltagedropatthecontactresistancebetweentwocarbonbrushesiscalledcontactvoltage.currentsharingIndex:1Page:1of:4SchunkKohlenstofftechnikTechnicalInformationThecontactresistancedependsonvariousparameters,Wementiononlythemostimportant•Collectorandambienttemper

5、ature•Peripheralspeed•Currentdensity•Brushpressure•Environmentalconditions•externalvibrations•frictioncoefficient•resistanceinthetampedcontact•brushgrade.....Twobrushesinparallelhavetwopointsofcommonpotential,thecollectorandthebrusharmfortheirterminals.Eachcurrentpathhast

6、heohmicresistanceofthepigtails,connectionsandbrushmaterial.Butthetotaloftheseohmiccomponentsisnegligiblecomparedwiththenon-ohmicresistanceattheinterfacebetweenbrushandcollector,whichisapprox.80%ofthetotalvalue.Ascanbeseenfromthefollowinggrapharelatively„slow“changeinvolta

7、gedropgivesaquitebigdifferenceincurrentdensityExample:Anychangeshouldgiveonebrusha5%highervoltagedropanda5%lessvalueforanotherbrush.Suchsmall,butquitecommonchangesinpracticalapplicationsareforexample:•Pressuredifferencesfromoneholdertotheother•contactchangesbyvibrationsor

8、•toosmoothsurfacescurrentsharingIndex:1Page:2of:4SchunkKohlenstofftechnikTechnicalInformationHav