Torque (Nm) = 9,549 × power (kW) ÷ speed (rpm). In US units, torque (lb-ft) = 5,252 × power (hp) ÷ speed (rpm). A 15 kW motor at 1,460 rpm delivers 98 Nm.
Where do 9,549 and 5,252 come from?
Power = torque × angular speed, and one revolution per minute is 2π ÷ 60 radians per second. 60 ÷ 2π × 1,000 = 9,549 for kW and Nm; 33,000 ÷ 2π = 5,252 for hp and lb-ft.
What is the starting torque of a motor?
A standard induction motor (NEMA design B or IEC design N) starts with roughly 150 to 250% of its rated torque and reaches a breakdown torque of 200 to 300%. The motor data sheet gives the exact values.
Does a gearbox change the torque?
Yes. A gearbox multiplies the torque by its ratio and divides the speed by it, minus losses of 2 to 5% per stage. A 98 Nm motor through a 10:1 gearbox gives about 950 Nm at 146 rpm.