# Using Inverters to Control Induction Motor Speed



## Lignin (Oct 13, 2012)

Hi All,

I'm building a bandsaw and would like to incorporate some sort of speed reduction to match the 4-pole induction motor I have, with the desired driven wheel speed. Using different sized drive and driven pulleys if fine in theory, and 1:7 would be okay. However, the contact angle on the drive pulley will make slipage quite likely under load. Introducing idlers and/or intermediate pulleys is not really an option in this case, so I was looking for an alternative. I was thinking that by using an inverter to reduce the mains frequency to approximately a third, the induction motor speed should also reduce to a third. Does anyone out there have experience with this technique?


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## DMS (Oct 13, 2012)

Most commercial inverters (at least the ones I have seen) have 3 phase output. In the US, possibly elsewhere, they are more commonly called Variable Frequency Drives, or VFDs. The trick is, you will need a 3 phase motor, so if the saw is single phase, you will need to replace the motor.


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## stevez (Oct 13, 2012)

As a mechanical engineer I work with variable frequency drives on occasion. I am always careful to understand the load imposed on the motor at all conditions. Sometimes a motor running at a nominal full speed meets or exceeds the load requirements yet as the speed of the motor is reduced the load can exceed the capability of the motor. Much of my work is with fans and pumps - and a modest drop in RPM usually means quite a  drop in horsepower required. Not every load behaves that way. The advantage a mechanical reduction system may have is that the motor can continue to develop rated HP - the reduction system increases the torque while dropping RPM. 

There might be some benefit to combining some reduction along with the variable drive. 

I do not want to make this difficult - just trying to help so that if you take time, spend money, you get what you want. 

Let me know if I can help. I am willing to bet that others here have experience - which may be of great benefit toward easing the task.

Steve


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## Lignin (Oct 14, 2012)

Hi,

Thanks for your thoughts guys. I'll go back to the drawings and see if I can fit an intermediate somehow. Definitely don't wish to reduce torque.

Cheers


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