motor amperage, PF & efficiency questions

Discussion in 'Homework Help' started by notoriusjt2, Apr 6, 2011.

  1. notoriusjt2

    Thread Starter Member

    Feb 4, 2010
    209
    0
    The following information is found on a motor nameplate:
    HP = 3/4
    voltage = 120/240
    freq = 60Hz
    RPM = 3450
    KVA = 1.0
    PF = .75
    Amps
    Eff. = 75%

    Calculate the watts used if the motor is operating at 240 volts...

    here is the math I used

    PF = True Power / Apparent Power
    .75=W/1000
    W=750
    A=W/V
    A=750/240
    A=3.125

    Is this the correct calculation?

    Also, I believe the efficiency is the ratio of the power in to the power out of the motor. When does this have to be accounted for in calculations? And how do you measure the power out of the motor? Power in would obviously be watts, but wouldnt the power out be somthing having to do with spinning a shaft such as work, or torque?

    Thanks
     
  2. notoriusjt2

    Thread Starter Member

    Feb 4, 2010
    209
    0
    or should it be like so..?

    A=VA/V=1000/240=4.16

    W=V*A*PF = 240*4.16*.75 = 748
     
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