How can I know the current a motor would require to run at a given RPM. Here are some values:

  • 160 HP motor
  • 325 volts
  • 2300 RPM
  • 311 ft/lbs of torque(not sure how useful this is)
  • induction motor
  • using a IGBT inverter to control PWM
  • 3 phase

I don't have a extensive background with electrical engineering and I am not quite sure where to start. I found a Tesla Motors data which was logged it seems it uses about 1000 amps but this is in MPH not rpm. I am not sure what is the drive ratio on the Tesla drive train to calculate RPM. Furthermore I am not too sure how would RPM variance affect current (hence why I wanna know which formulas are use to calculate this)

Tesla Motor data: https://drive.google.com/open?id=0B_bX3Zu4zvgYX1RYYmR1RnZVUG8

Do I need to get somebody to measure Tesla winding resistance to be able to calculate it for Tesla Motors? Is there any other number I need that can only be gotten from a real/already built motor?


1 Answer 1


The RPM is determined by the frequency and does not directly effect the current. The current is more closely related to torque. Some useful relationships are:

Motor speed RPM = 120 X Frequency (Hz) / Number of motor poles (4 poles for the Tesla I think)

Input power to the motor, Watts = Volts X Amps X Square Root of 3 X Power Factor

Horsepower output = Torque (Ft-Lbs) X RPM / 5252

Input Power X Efficiency = Output Power

1 Horsepower = 746 Watts

The Tesla motor is very efficient, 0.95 or higher

For constant torque operation, the voltage applied to the motor is proportional to frequency.

The Tesla motor can provide constant torque up to some frequency limit. Above that, the voltage does not increase any more (or perhaps it increases at a slower rate). That allows the motor to provide constant power.

Re. Test Data

It appears that the voltage and current for the test data are battery voltage and current. The power at the battery is just watts = voltage X current. The inverter is between the battery and the motor. The Tesla inverter efficiency is also quite high, perhaps 0.95 or higher.

  • \$\begingroup\$ How do you determine power factor is that the same as efficiency? Does it vary between the start of the motor frequency range and the end? \$\endgroup\$
    – Annerajb
    Apr 8, 2016 at 1:28
  • \$\begingroup\$ The power factor is a characteristic of the motor design like efficiency. It varies a lot with current, but it also varies somewhat with voltage. If the frequency changes power factor will stay relatively constant if the ratio of voltage to frequency is kept constant. \$\endgroup\$
    – user80875
    Apr 8, 2016 at 2:45

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