Efficiency
The ratio of the output power delivered to the motor to the input power drawn from the supply. The difference turns entirely into heat: a driver running at 95% efficiency and delivering 300 W produces roughly 16 W of loss. Efficiency directly determines both the cooling requirement and, in battery systems, the operating time.
In a DC driver the loss consists of three main items: the conduction loss of the switches, the switching loss during turn-on and turn-off, and the diode loss in the freewheeling path. To these are added the board traces, terminal and cable resistance.
- Load dependence: Efficiency is not a fixed number. At very light load the board's own consumption dominates so efficiency is low; it rises as the load increases, then starts to fall again because conduction loss grows with the square of the current.
- Voltage effect: Delivering the same power at 24 V means half the current compared with 12 V; conduction loss drops to a quarter. This is the most concrete gain of choosing a 24 V system instead of 12 V.
- Whole-system view: Even if the driver efficiency is high, cable and terminal losses pull the total efficiency down.
An efficiency percentage is not stated in AXI product data; for your own application you need to calculate the loss budget from the current, cable cross-section and operating point.
The context in which this term is used: DC Motor Driver Selection Guide