How is current calculated from motor power (W)?
The rough calculation is done with I = P / V; 180 W at 12V is roughly 15 A, and the same power at 24V is roughly 7.5 A. However, the output power printed on the label is mechanical; because of motor efficiency the actual current drawn is higher. For an exact result, measure with a clamp meter under load.
Use the basic relation: I = P / V. Examples:
- 12V, 180 W -> 15 A
- 24V, 180 W -> 7,5 A
- 12V, 360 W -> 30 A
This calculation has two traps. The first is whether the value on the label is mechanical output power or electrical input power. If output power is stated, the actual current will be noticeably higher than calculated because of motor efficiency. The second is that the calculation is only valid for steady operation; starting current is typically 5-8 times the nominal value.
So use the calculation as a first filter and base the selection on measurement. Compare the result against the product ratings:
- KS250: 15 A continuous, 45 A peak (5 s).
- PT500: 30 A continuous, 40 A maximum (15 s).
If the calculated result approaches the driver's continuous rating, no safety margin is left. On paper a 180 W motor at 12V sits exactly at the limit of the KS250; in that case either moving to 24V or stepping up to the PT500 is the safer choice.
Full topic: DC Motor Driver Selection Guide