I am working on a design and need to calculate the energy consumption of this motor:

https://www.maxonmotor.com/medias/sys_master/root/8825428410398/17-EN-256.pdf. (Part No. 339252)

The manufacturer's specifications states:

Nominal current (max. continuous current): 0.402 A and Nominal voltage: 12 V.

Based on this, my understanding is that the power consumption of the motor should be 0.402 A x 12 V = 4.824 watt

However the manufacturer lists this motor as 1.5 W.

How is this adding up? Shouldn't this be a 4.8 W motor? Can you please help me understand how the current (0.402 A) and voltage (12 V) and power (1.5 W) are related? Is there anything else in that specification sheet that I am missing?

  • 1
    \$\begingroup\$ You're missing one piece of the equation - the load on the motor. Voltage, current, and torque are related. \$\endgroup\$
    – Steve
    Aug 12, 2018 at 23:40

1 Answer 1


It's right there on page 1 of the data sheet. The graph below shows the power output curve being 1.5 watts: -

enter image description here

What you have calculated is the electrical input power and this does not equal the mechanical output power (\$2\pi n T\$).

Take the example at 10,000 rpm. That's 167 revs per second (n above). Multiply it by torque (approximately 1.4 mNm) and you get 0.2333. Multiply by pi and 2 and you get a wattage of 1.47 watts. That's the output power.

  • \$\begingroup\$ And to help clear that up, the \$\endgroup\$
    – JRaef
    Aug 20, 2018 at 19:21
  • 1
    \$\begingroup\$ To help clear that up, the "rating" of an electric motor is the MECHANICAL OUTPUT, i.e. torque at a given speed, expressed in W in many parts of the world, HP in others (although HP can be converted to W by simply dividing by 746, i.e. there are 746W/HP). The ELECTRICAL power consumed by an electric motor is referred to as the "absorbed power" and is always different from the mechanical output power, by virtue of efficiency in the process of converting electrical energy into kinetic energy. Unfortunately, absorbed power is ALSO expressed in Watts, hence the (frequent) confusion. \$\endgroup\$
    – JRaef
    Aug 20, 2018 at 19:28

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