0
\$\begingroup\$

I am trying to power a brushless motor with a max current consumption of 12.5 A (specified in datasheet). How should I figure out the maximum current drawn by one of the phases of the ESC? Should I just divide the max current draw of the motor by three, or is the solution more complex?

\$\endgroup\$
  • \$\begingroup\$ ESC's in the sense of hobby speed controllers are typically rated in terms of the net draw (ie, from the battery not per phase); except that they are also typically over-rated with a "marketing optimism factor" which likely overwhelms the distinction. Either pick something with a healthy safety factor or consult actual experiential reviews of a given product. \$\endgroup\$ – Chris Stratton Aug 5 at 1:10
  • \$\begingroup\$ I am actually wondering about current from esc output to one of the three motor wires. \$\endgroup\$ – Saunders Aug 5 at 1:12
1
\$\begingroup\$

With 6 step commutation each phase wire is connected for 2 out of every 3 steps, so as a rough guide you can assume that it conducts 2/3 of the average motor current. That means you can generally get away with motor wires that are one gauge smaller than the battery wires.

Getting a more exact figure is harder because the current waveform varies depending on motor characteristics and throttle level. Below is an example scope trace of current in one phase wire of a brushless model aircraft motor. In this case the battery current was measured at 15.4A. We see that current is flowing for 2 out of every 3 steps, and the current during this time is fairly flat at ~16A. Therefore the average current over a full cycle should be ~11A and the rms current should be ~13A.

enter image description here

And here's the same motor running at part throttle on a higher voltage battery, showing the effect of PWM:-

enter image description here

In this case the battery current was only 10.3A, but the waveform has become triangular and peaks at ~32A. The average and rms currents are still ~11A and ~13A, but are now higher than the battery current.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.