Motor Amp Formula with an RPM Change
New Motor Amps Calculation:
Example: How will the Amps of the motor go up if a Service Technician goes from 400 RPM to 475 RPM on a blower?
The blower motor is pulling 8 Amps.
The FLA of a motor is 12 Amps.
Rated HP of the Motor is 5 HP.
New motor Amps= Exist Amps x [(New RPM )/(Exist RPM)]^3
Step 1: New motor Amps= 8 x [(475 RPM )/(400 RPM)]^3
Step 2: New Motor Amps = 8 x 1.18753
Step 3: New Motor Amps = 8 x 1.674
Step 4: New Amps = 13.39 Amps
Amps increased by the cube of the Change in RPM. It’s not a linear conversion. The example above 475 RPM / 400 RPM was 1.1875 or a 118% increase in rpm. The new amps 13.39 / 8 amps is 1.67375 or a 167% increase in required amps!