BooTENDS TnRoITIoNAL SuurTERs STEp TooI Box ... - Wood Tools

Heovy MetolThough other factors are involved,what best determines a motor'sactual power output and resistanceto temperature rise are theamounts of iron and copper in itsrotor, stator, and windings. Thesematerials conduct current and actas a thermal sink for the heat createdby the flow of electricity.If youVe ever overfed a piece ofwood into a blade or cutter, youknow it's possible to stall a motor byexceeding its torque limit. Butbetween that abrupt limit and themotor's normaload range, there's awide expanse where continuedpeak demand will create more heatthan the motor is designed to withstand.Every time a motor gets inthat elevated temperature range,the coating of clear enamel insulationon the copper windingsdegrades. If the periods of overheatingare frequent or severe, theinsulation can eventually melt oreven burn, ruining the motor.Better-quality motors have adequately sized windings that offer awider margin of protection againstheat damage. They also have someform of thermal overload protection.These devices act like circuitbreakers that trip an overheatedmotor off and can't be reset until itcools down. Wood shop motorsFrame size (Mountingplate and rotor shaftsize/position)HorsepowerratingVoltageoptionsAmperageratingMotorspeedPulse cycle ofincoming cunent(per second)Service factor(Retlects built-in overloadcapacity; e.g. 1.25= 25o/omargin above normal rating.)7 .413.5-3.7should have only manual (pushbutton)thermal protectors. Automaticresettypes can turn machines onagain without any warning.Checking ReferencesThe nameplate reveals a lot abouta motor, but the warranty can alsobe a clue to quality. Sometimesthere's fine print there about themotor's intended application or anexclusion for commercial use. Ifyou're shopping for equipment,Used in portable and bench top powertools, universal motors pack more punch per poundthan induction motors, but aren't designed to withstand long run times, Power ratings arein amps; any horsepower ratings are likely to be for peak hp, not continuous.Fulload efficiency(look for 50-80% efficiencyvarieswith motor size)nr'l'fi-,Wiring diagramsfor low andhigh voltagelnsulation classDuty rating @ 40"C.(104'F.) ambienttemperatureAmperage draw@ service factor overloadask specifically about the warrantyon the electricals, since it may differfrom the coverage on themachine itself.Also, look for independent certification.Most U.S. manufacturerscomply with National ElectricalManufachrrers Association (NEMA)standards, so there's less room forstretching performance claims.North of the border, look for theCanadian Standards Association(CSA) symbol.In addition, check for a certificationstamp from UnderwritersLaboratories. UL listing meansthat an electrical product has metthat agency's standards for safedesign and operation. They don'ttest motors for actual power output,but by running them both atand beyond their rated amps andmeasuring the temperature rise,they answer the question indirectly.If the motor maintains itsrated amperage under a continuousload and stays within the designatedtemperature range, thetest confirms that the output is acontinuous horsepower rating.Translation: There's room for themotor to run intermittently athigher peak levels, without dangerouslyoverheating. tF56\Torkbench t}une 1997