HomeMotorsMotor rating determines and replaces

Motor rating determines and replaces

What motor rating is used is determined by the amount of torque required to move the load. Horsepower does not move the load, torque moves the load. A 1-hp, 6-pole motor will develop 50% more torque than a 1-hp, 4-pole motor If the manufacturer of the agitator is provided with the density of the material beforehand they should determine what torque is required and supply a motor to suit. If the original motor is going to be used it may be necessary to shave some material off of the agitator blade.

Always remember a motor is a "dumb" device and will try to drive a load independent of the torque/horsepower required. In easiest terms this 1hp motor will always try to move the load at its design speed (pole design) with applied frequency N=120F/P . The issue is the impeller is incorrect and should be changed to reflect the mechanics of the application. This will involve as you are aware, viscosity of material, speed, vessel mechanics (diameter/depth/venture effect), etc.

It is possible to reduce the speed if a 3 phase motor is used with VFD and ultimately reduce the load but the mechanics and desired mixing may then be affected. The best way to change is either replaces the motor with the correct horsepower/kW, use a different ratio gearbox or change mixing impeller.

It is possible to use a motor in the service factor but issues such as ambient, excessive heat, humidity, etc. will affect the life of the motor. The rise of 10* C over design will reduce the life of a motor by 50% over a long term exposure. Class H insulation will reduce this slightly or just offset the design temp rise factor, not change the fact that additional torque is required to drive the load. 1hp at 1800rpm will produce 3 lb/ft of torque. The only way to change this is to increase the horsepower or change the impeller to reflect 1 hp. load.

You may like:

Buy VFD on
Buy Variable Frequency Drives (VFD) online, direct sale by manufacturer with wholesale price.


AC Motor Control