Here’s a quick reference for common fractional horsepower motor equations.
Basic Motor Equations
Torque [lb-ft] = (Horsepower * 5,250) / RPM
Torque [lb-in] = (Horsepower * 63,025) / RPM
Horsepower = (Torque [lb-ft] * RPM) / 5,250
Horsepower = (Torque [lb-in] * RPM) / 63,025
Time for motor to reach operating speed (seconds)
Seconds = (WK² * Speed Change) / (308 * Avg Accelerating Torque)
WK² = Inertia of Rotor + Inertia of Load [lb-ft]²
Avg Accelerating Torque = (((Full Load Torque + Breakdown Torque) / 2) + Breakdown Torque + Locked-Rotor Torque) / 3
Load WK² [at motor shaft] = (WK² [load] * Load RPM²) / Motor RPM²
Belt Speed [FPM] = .626 * RPM * Diameter [in]
Chain Tension [lbs] = (33,000 * Horsepower) / Chain Speed [FPM]
Ohm’s Law
Ohms = Volts / Amperes [R = E / I]
Volts = Ohms * Amperes [E = R * I]
Amperes = Volts / Ohms [I = E / R]