Single Phase AC Induction Squirrel Cage Motors - Aerovent

Single-phase AC motors are not all equal. There are fivebasic types, all with different operating characteristicsand capabilities. As it has been shown, the differencesbetween each motor type are great enough that it isimportant for the user to understand each motor type,where it makes sense to apply them and how to applythem.What does knowing the previous technical informationon these five types of motors have to do with fans?The answer is simply this: almost every commercial fanis powered by an electric motor and other than the fanwheel it is by far the most important component of afan. The motor is the most likely component to fail in afan and a large percentage of fan motor failures can beattributed to poor selection and application of themotor.SummarySpeed control capability is also becoming more commonplacetoday (especially on direct drive fans) andapplying today’s speed controllers to any single-phaseAC motor can prove disastrous. It is important to understandthat there are only two types of single-phase ACsquirrel cage motor types that are suited for speedcontrol applications.Understanding the starting characteristics of eachmotor type is another area of importance for the motorapplication to a particular fan. All five motor types havedistinct starting characteristics that need to be properlymatched with the fan starting characteristics.The table below can be used as a quick referenceto the five motor types along with typical (acceptable)fan applications for each motor type.Table 6. Summary of Five Single-Phase Motor TypesMOTOR TYPE SPLIT-PHASE CAPACITOR-STARTDESCRIPTIONStart winding connectedin parallelwith main winding,connection controlledby centrifugal switchor relay.Identical to the splitphasedesign exceptincludes the additionof a capacitor inseries with the startwinding circuit.PERMANENTLY SPLITCAPACITORStart winding permanentlyconnected inparallel to main windingwith a continuousduty capacitor in thecircuit at all times.CAPACITOR START-CAPACITOR RUNCombination ofcapacitor-start andPSC type motor. Startwinding permanentlyconnected in parallelto main winding witha continuous dutycapacitor in the circuitat all times andcapacitor in serieswith the start windingcircuit.SHADED POLESingle main windingwith shadingcoils for providingstarting torque.HP RANGE 1/6 to 1 1/4 to 2 1/100 to 1 3/4 to 20 1/1000 to 1/4TYPICAL RATED 860, 1140, 1725,3450EFFICIENCYRANGE860, 1140, 1725,34501050, 1625, 3250 1725, 3450 1050, 1550, 310050 to 60% 50 to 60% 55 to 65% 55 to 65% 20 to 40%POWER FACTOR 60 to 70% 60 to 70% 80 to 100% 80 to 100% 50 to 60%STARTINGTORQUE 100% Up to 300% 50 to 80% Up to 300% 40 to 50%TYPICALSuitable for frequentstarting of fans inboth direct and beltdriven units.All-purpose motor forhigh starting torque,low starting currentused in both directand belt driven units.Intended for directdrive models andapplications requiringspeed control.All-purpose motor forhigh starting torque,low starting currentused mainly in largerbelt driven units.Suitable for directdrive low powerfans and multispeedapplications.ADVANTAGESa. Good startingtorque.b. Medium efficiency.a. High startingtorque.b. Lower startingcurrent than splitphase design.a. High runningefficiency.b. Capable of multispeedoperation.c. Can be used withspeed controldevices (i.e., triacs).d. Quietest of allsmall inductionmotors.a. High startingtorque.b. Lower startingcurrent than splitphasedesign.c. Available in largerHP sizes thancapacitor-start orPSC motor types.d. High runningefficiency.a. Inexpensive tomanufacture.b. Multi-speedoperation.c. Compact.DISADVANTAGESa. Not suited forhigh startingtorque loads.b. Not applicable forspeed control.c. High starting currenta. More expensivethan split-phasedesign.b. Not applicable forspeed control.a. Low startingtorque.b. Speed varies moreunder load.a. Most expensivesingle-phase motortype.b. Not applicable forspeed control.a. Low efficiency.b. Low startingtorque.10 Fan Engineering FE-1100