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Key information May2010edition/subjecttochange

maxon DC motor and maxon EC motorKeyinformation

The motor as an energy converter

TheelectricalmotorconvertselectricalpowerPel(currentIandvoltageU)intomechanicalpowerPmech(speednandtorqueM).Thelossesthatarisearedividedintofrictionallosses,attributabletoPmechandinJoulepowerlossesPJofthewinding(resistanceR).IronlossesdonotoccurinthecorelessmaxonDCmotors.InmaxonECmotors,theyaretreatedfor-mallylikeanadditionalfrictiontorque.Thepowerbalancecanthereforebeformulatedas:

Thedetailedresultisasfollows

Electromechanical motor constantsThegeometricarrangementofthemagneticcircuitandwindingdefinesindetailhowthemotorconvertstheelectricalinputpower(current,voltage)intomechanicaloutputpower(speed,torque).Twoimportantcharac-teristicvaluesofthisenergyconversionarethespeedconstantknandthetorqueconstantkM.ThespeedconstantcombinesthespeednwiththevoltageinducedinthewindingUind(=EMF).Uindisproportionaltothespeed;thefollowingapplies:

Similarly,thetorqueconstantlinksthemechanicaltorqueMwiththeelectricalcurrentI.

Themainpointofthisproportionalityisthattorqueandcurrentareequivalentforthemaxonmotor.Thecurrentaxisinthemotordiagramsisthereforeshownasparalleltothetorqueaxisaswell.

Seealso:Technology–shortandtothepoint,explanationofthemotor

Motor diagrams

AdiagramcanbedrawnforeverymaxonDCandECmotor,fromwhichkeymotordatacanbetaken.Althoughtolerancesandtemperatureinfluencesarenottakenintoconsideration,thevaluesaresufficientforafirstestimationinmostapplications.Inthediagram,speedn,currentI,poweroutputP2andefficiencyhareappliedasafunctionoftorqueMatconstantvoltageU.

Speed-torque lineThiscurvedescribesthemechanicalbehaviorofthemotorataconstantvoltageU:– Speeddecreaseslinearlywithincreasingtorque.– Thefasterthemotorturns,thelesstorqueitcanprovide.Thecurvecanbedescribedwiththehelpofthetwoendpoints,no-loadspeedn0andstalltorqueMH(cf.lines2and7inthemotordata).DCmotorscanbeoperatedatanyvoltage.No-loadspeedandstalltorquechangeproportionallytotheappliedvoltage.Thisisequivalenttoaparallelshiftofthespeed-torquelineinthediagram.Betweentheno-loadspeedandvoltage,thefollowingproportionalityappliesingoodapproximation

whereknisthespeedconstant(line13ofthemotordata).

Independentofthevoltage,thespeed-torquelineisdescribedmostprac-ticallybytheslopeorgradientofthecurve(line14ofthemotordata).

Derivation of the speed-torque lineThefollowingoccursifonereplacescurrentI withtorqueMusingthetorqueconstantinthedetailedpowerbalance:

TransformedandtakingaccountofthecloserelationshipofkMandkn,anequationisproducedofastraightlinebetweenspeednandtorqueM.

orwiththegradientandtheno-loadspeedn0

UnitsInallformulas,thevariablesaretobeusedintheunitsaccordingtothecatalog(cf.physicalvariablesandtheirunitsonpage42).42).).

Thefollowingappliesinparticular:– AlltorquesinmNm– AllcurrentsinA(evenno-loadcurrents)– Speeds(rpm)insteadofangularvelocity(rad/s)

Motor constantsSpeedconstantknandtorqueconstantkMarenotindependentofoneanother.Thefollowingapplies:

Thespeedconstantisalsocalledspecificspeed.Specificvoltage,generatororvoltageconstantsaremainlythereciprocalvalueofthespeedconstantanddescribethevoltageinducedinthemotorperspeed.Thetorqueconstantisalsocalledspecifictorque.Therecip-rocalvalueiscalledspecificcurrentorcurrentconstant.

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