Power consumption using Actual current on CAN

Electronics
1

Hi,

I have been using one leg (2 dof) quite successfully with position control after building on the BLMC drivers software. I am using a 24V power supply. I am measuring Iq actual using CAN and want to measure the power (W) and energy consumption (WH). What Voltage should I multiply the current by? 24V does not sound correct because the actual current shown on the digital display of the power supply unit is much less than the Iq actual being read. Is it 5V ? 3.3V? I have read the details of the Launchpad, DRV 8305 and the FOC manuals, but am confused.

Thanks,

Vijay

2

Hello, the Iq current is actually the current at the motor side. The motor voltage is modulated by the driver (PWM) from the bus voltage to regulate the motor current. It is normal that it is less than the power supply. The driver doesn’t report the motor voltage. It is proportional to the motor speed + motor resistance times motor current.

Hope this helps,
Best,
T.

3

Thomas,

Thanks for the prompt reply! Yes, a good reminder that its BLDC with FOC!

So, instead if I use

  1. Power (P) = Torque (T) x Angular velocity (w)
  2. Since T = 0.025 x I and w is also measured, would this be a fair reflection of at least the Mechanical Power / Output Power and form the bulk of the consumption? (sorry i know its high school Physics :))

Vijay