Vfd And Very Low Torque

Everything you describe makes me think motor is wired for 440 rather than 220.
 
Ow hello, i just had a read of the manual, i hadn't realised they were voltage doubling vfd's

Stuart
 
You have bumped into the constant HP curve. Which is to say at low speed you tend to make larger cuts which require more torque while you make finishing cuts at higher speeds/lower torque. torque load is not controllable in the drive it is a function of the load. Variable torque and constant torque refer to how the drive is loaded as the drive cannot push more current (torque) to the motor. second issue is speed range this is the ratio of maximum speed/ minimum speed that the system (drive and motor) can operate at full torque/current without slowing down. Lesson motors are generally good for a 10:1 to 20:1 speed range. Depending on the drive mode of operation (volts/Hz, Sensorless vector, flux vector, force vector) you can operate from a speed range of 10:1 (volts/Hz) to 2000:1 (flux/force vector mode). Generally speaking 10:1 is about all you need. The bad news is the GS2 Automation direct drive is a Volts/Hz drive and there is little you can do to improve the performance by changing parameters in the drive. the one parameter that could improve the low speed torque is the boost setting in the drive.

But there are things you can do to improve performance of the system. first the small pulley needs to be on the motor as this multiplies the torque delivered to the machine. What I suggest is do not remove the pullies on your machine. Find the belt ratio that works best for you most of the time with the motor running at full speed. Then adjust the belt to the next slower belt ratio. Now here is the "trick" that will make things work better. set the maximum frequency of the drive to 120Hz this will cause the motor to run at 3600 RPM. I am assuming you have a 1750 RPM motor. this will not cause damage to the motor as long as it is not a sleeve bearing motor which is not likely. The only major deference between a 1800 RPM motor and a 3600 Rpm motor is the number of poles in the windings they are mechanically the same. Now you have doubled the speed range of the system but more importantly you have increased the mechanical advantage of the system so that you will have much more torque in the lower speed ranges whare you need it. If you find that you seldom operate the drive at 120Hz (3600) rpm then adjust the belts to the next lower speed and you will have even more torque at the lower speeds.

Things to watch out for. Do not run the drive past half speed (60 Hz/1800 RPM) if you have a large pulley on the motor and the smallest pulley on the machine. With the over speed you could potentially get the spindle running at well over 10,000 RPM and things will not go well at that speed. Vibration could also be an issue on smaller lathes and mills at the higher speeds. make sure that there are no chips or cracks in the motor pulley if there are replace the pulley.


Jim Nunn
 
Jim Nunn said:
You have bumped into the constant HP curve. Which is to say at low speed you tend to make larger cuts which require more torque while you make finishing cuts at higher speeds/lower torque. torque load is not controllable in the drive it is a function of the load. Variable torque and constant torque refer to how the drive is loaded as the drive cannot push more current (torque) to the motor. second issue is speed range this is the ratio of maximum speed/ minimum speed that the system (drive and motor) can operate at full torque/current without slowing down. Lesson motors are generally good for a 10:1 to 20:1 speed range. Depending on the drive mode of operation (volts/Hz, Sensorless vector, flux vector, force vector) you can operate from a speed range of 10:1 (volts/Hz) to 2000:1 (flux/force vector mode). Generally speaking 10:1 is about all you need. The bad news is the GS2 Automation direct drive is a Volts/Hz drive and there is little you can do to improve the performance by changing parameters in the drive. the one parameter that could improve the low speed torque is the boost setting in the drive.

But there are things you can do to improve performance of the system. first the small pulley needs to be on the motor as this multiplies the torque delivered to the machine. What I suggest is do not remove the pullies on your machine. Find the belt ratio that works best for you most of the time with the motor running at full speed. Then adjust the belt to the next slower belt ratio. Now here is the "trick" that will make things work better. set the maximum frequency of the drive to 120Hz this will cause the motor to run at 3600 RPM. I am assuming you have a 1750 RPM motor. this will not cause damage to the motor as long as it is not a sleeve bearing motor which is not likely. The only major deference between a 1800 RPM motor and a 3600 Rpm motor is the number of poles in the windings they are mechanically the same. Now you have doubled the speed range of the system but more importantly you have increased the mechanical advantage of the system so that you will have much more torque in the lower speed ranges whare you need it. If you find that you seldom operate the drive at 120Hz (3600) rpm then adjust the belts to the next lower speed and you will have even more torque at the lower speeds.

Things to watch out for. Do not run the drive past half speed (60 Hz/1800 RPM) if you have a large pulley on the motor and the smallest pulley on the machine. With the over speed you could potentially get the spindle running at well over 10,000 RPM and things will not go well at that speed. Vibration could also be an issue on smaller lathes and mills at the higher speeds. make sure that there are no chips or cracks in the motor pulley if there are replace the pulley.


Jim Nunn
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Thanks for your very informative message. You have excellent presentation skills.
 
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