What is the power consumption of a controller?

Topic:

• What is the current draw resp. power consumption of a motor controller?

Solution:

The power consumption of a controller sums of the power consumption …

• … of its internal electronics
  e.g. processor, memory, DC/DC converters, logic control, …
• … of any connected peripherals
  e.g. encoders, hall sensors, sensors, actuators, brakes, ...
• … due to motor’s current draw at its working point.

The current draw of a controller's internal electronics including the typically connected sensors is often in the range of 100 … 200 mA resp. just some Watt totally. This current draw or power consumption can be neglected in most cases when the motor is active and moving a load. 

The motor controller’s power stage works like a power converter with a high efficiency of typically 95 ... 98%. The input current draw of the motor controller, which is caused by motor operation, can be roughly calculated based on the motor's operating point (= speed and torque) and the controller's supply voltage like described by the following public Support Center documents:

• Motor controllers: Input current versus Motor current, Power Conversion 
• EPOS4 / IDX: Calculation of the electrical motor power

Special aspects of battery powered devices?

In case of a battery powered device the controller’s and peripherals’ current draw in “Disable” state gets more important. This current draw finally depends on the controller's internal electronics and the effectively connected and active encoders, any kind of sensors, and the state of actuators. The controller's operational state can also have some minor influence. Therefore, it is not possible to specify a binding value without knowing about the concrete system environment and system state. Even then it is quite demanding and quite time-consuming to calculate the current draw based on lots of data sheets and assumed sensors' and actuators' state. It is more efficient and recommended instead to check the input current draw of the motor controller with all sensors and actuators connected by some measurement. Ultimately, such a very simple measurement of the motor controller's input current with a multimeter is always the best way to obtain a reliable characteristic value for a system environment and its concrete operating state.

Additional note:

The specified motor data (and probably the current draw of more powerful actuators (e.g. a brake) has some tolerances of typ. ±10%. This means that the actual current draw even in case of a defined motor’s torque output can slightly vary later on depending on the concrete (identical) motor or actuator (e.g. brake) out of a production series. In case of powerful motors this variation of motor’s or actuator's current draw is often higher than the current consumption of the controller’s internal electronics or its external peripheral sensors.

Cross reference:

• What is the power consumption of a brake?