Rated Current
It is the current a motor can safely draw at its rated load with no time limit, and it is the value printed on its label. It is determined so that the winding temperature stays within the permitted limit. It is the starting point for driver, cable and fuse selection, while peak currents are assessed separately.
Measuring the system's real current instead of the label current always gives a more accurate result, because the same motor can run well below or above its rating depending on the application. Take the measurement under the hardest load, over the full stroke, and if possible watch the current waveform so you do not miss the peak values.
Selection logic:
- The driver's continuous current capacity must be above the worst-case continuous current measured. The KS250 is listed with a continuous rating of 15 A and the PT500 with 30 A.
- Leave a reasonable safety margin; keeping the continuous current in the 70–80 percent band of the driver capacity gives thermally comfortable operation.
- The fuse is generally chosen at 125–150 percent of the continuous current and protects the cable.
The relation P = V × I is used to estimate current from motor power; a 24 V, 250 W motor draws roughly 10,4 A, and this value goes up somewhat once efficiency loss is taken into account.
Context where this term is used: DC Motor Driver Selection Guide