What amperage fuse should I fit to the motor driver?
The general rule is 125-150% of the continuous current; some sources recommend the 135% practice. In an application drawing 15 A continuously that means roughly a 20 A fuse. Remember that the fuse protects the cable: the chosen cross-section must be able to carry the fuse rating.
Three inputs determine the fuse rating:
- The continuous current under load. Measure it with a clamp meter, do not trust the label.
- The starting pulse. Starting current is typically 5-8 times the nominal current and lasts 0,5-3 seconds. The fuse's time-current curve must pass this pulse without blowing.
- Cable cross-section. The fuse protects the cable, not the driver. The cross-section must be able to carry the current the fuse lets through safely.
Calculation: fuse rating ≈ continuous current x 1,25-1,50. Examples:
- 10 A continuous -> 12,5-15 A range
- 15 A continuous (KS250 at full capacity) -> 19-22 A range
- 25 A continuous -> 31-37 A range
Choosing the characteristic is at least as important as the rating: ATO/blade type fuses are generally of the fast-blow character and may blow needlessly on the motor starting pulse. For motor loads choose a slow-blow (T/TT) character or a time-current curve that covers the starting pulse.
Place the fuse as close as possible to the supply source, preferably at the first point out of the battery terminal; what needs protecting is the whole cable in between.
Full topic: DC Motor Driver Selection Guide