How can I control the RPM of an industrial motor of 7 horse power? I need it to have high torque and low RPM, like 100 per minute.
*For stepless control of AC motor, you need to have a VFD [variable frequency drive]. Basic equation is: RPM=120*frequency/no. of poles here,no of poles are fixed for your motor and 120 is constant. So, to control the RPM you have to change the frequency. 100/120=frequency/no of poles 0.83 =frequency/no of poles check the no of poles of your motor and put in the above formula,you will get the frequency. #Example A 4-pole motor that is connected directly to 60 Hz utility (mains) power would have a synchronous speed of 1800 RPM: 60*120/4=1800 If the motor is an induction motor, the operating speed at full load will be about 1750 RPM. If the motor is connected to a speed controller that provides power at 40 Hz, the synchronous speed would be 1200 RPM: 120*40/4=1200 #A variable-frequency drive (VFD) is a system for controlling the rotational speed of an alternating current (AC) electric motor by controlling the frequency of the electrical power supplied to the motor. A variable frequency drive is a specific type of adjustable-speed drive. Variable-frequency drives are also known as adjustable-frequency drives (AFD), variable-speed drives (VSD), AC drives, microdrives or inverter drives. Since the voltage is varied along with frequency, these are sometimes also called VVVF (variable voltage variable frequency) drives. #Adjustable speed drive (ASD) or variable-speed drive (VSD) describes equipment used to control the speed of machinery. Many industrial processess such as assembly lines must operate at different speeds for different products. Where process conditions demand adjustment of flow from a pump or fan, varying the speed of the drive may save energy compared with other techiques for flow control. Where speeds may be selected from several different pre-set ranges, usually the drive is said to be adjustable speed. If the output speed can be changed without steps over a range, the drive is usually referred to as variable speed.
All sealing fans are AC motors. You can use a variable resistance or stepped resistance. This is not an accurate method. The speed can also be controlled by varying the frequency. This method is accurate and expensive.
If you have a way to decrease the AC input frequency thats the easiest way. Depending on the application of the motor you can have it maintain a certain RPM and simply change the power to it (by changing the amps applied) to change the HP it puts out, but that is really only certain applications
Definitely do your homework before buying, though. If you just size the drive to the motor horsepower, you may end up with too small a drive and a lot of expensive smoke.
