Estimating power need of motor drive system

From Granite Devices Knowledge Wiki
Jump to: navigation, search

Estimating the need of power supply wattage for motor drive can be a complex task and may require experimentation. The needed electrical power depends on the actual mechanical load and use of motor. The power demand is proportional to the product of motor speed and torque. The following table summarizes the relation between speed and torque vs power.

Moving slowly Moving fast
Producing low torque Very low power consumption Low to medium power consumption
Producing high torque Low to medium power consumption High power consumption

Calculations[edit | edit source]

Instantenous electrical power demand of motor can be estimated from the equation:

$ P_{electrical} [W] = \frac{Torque [Nm] * Speed [RPM]}{0.095488*efficiency [%]} $

Example:

  • we assume efficiency of motor being 80% and drive efficiency 97%, which makes total efficiency of 0.80*0.97 = 0.776 = 77.6%.
  • motor rotates at 1000 rpm and during maximum instatenous load it outputs 2 Nm peak torque

Instantenous input power becomes:

$ P_{electrical} [W] = \frac{2 Nm * 1000 RPM}{0.095488*77.6}=259.9 W $

PSU sizing guide[edit | edit source]

In overall, PSU should be sized so that it does not overload or overheat during any condition in machine use. Since servo systems typically have greatly varying load, to find minimum sufficient PSU size might require measurements from the actual machine. To esimate minimum sufficient PSU size, measure RMS power consumption of the system during at least 10 second period of heavy use.

If measurements can't be done, then maximum RMS power load can be estimated roughly by summing rated power values of motors in the system. However, in typical machines the average power consumption is significantly less than summed motor power.


In no event the Product Information or parts hereof shall be regarded as guarantee of conditions or characteristics. The Product Information or any part thereof may also not be regarded as a warranty of any kind. No liability of any kind shall be assumed by Author with respect to Product Information or any use made by you thereof, nor shall Author indemnify you against or be liable for any third party claims with respect to such information or any use thereof.

As content of this Wiki may be edited by user community, Granite Devices Oy or it's affiliates do not take any responsibility of the contents of this Wiki. Use information at your own risk. However, Granite Devices staff attempts to review all changes made to this Wiki and keep information trustworthy.

Without written consent, Granite Devices' Products or Intellectual Property shall not be used in situations or installations where living beings, material property, or immaterial property could be harmed by the operation, features or failures of Product. Products may only be used in a way where hazards like moving parts, electric shock, laser radiation, or fire can't be realized even if the content of this Wiki would suggest otherwise.