# Vfd And Very Low Torque



## Transformer (Mar 20, 2015)

On my lathe I have replaced my motor with a 3 phase 230 volt 1 hp Leeson motor.  I am running this through a VFD from Automation Direct with 120 volt input, model is GS2-11P0.  I have gone through the manual to set the VFD parameters where I think they should be and I can give further details.  I was running my belt from the largest pulley on the motor to the smallest pulley on the spindle which was giving me about 2000 max RPM. 

This is a recent CNC conversion and I have only been cutting plastic as I familiarized myself with things.

On to steel.  On a .002 facing cut on 1.5" rod at 600 RPM running from the centre of the piece outward the lathe stalled at about the half way point.  Increased the speed to 800, still stalled out.  Backed everything off, increased speed to 2000 RPM, used my hand around the rod and I was able to stop rotation fairly easily.  Then changed the belt to smallest at the motor to largest at the spindle, which gave a max of about 750 RPM and I could still hand stop the rotation.  This thing just has no torque.

Changing the P2.00 setting from 00 general purpose to 01 high starting torque did not make any difference.  When I changed this setting to 02 fans and pumps the motor did not turn at all.

First of all, do I have a problem or is this all I can expect from this motor/VFD combination?  If I do have a problem where might I look to try and resolve it?  All suggestions appreciated.  Also I can provide further info on my settings if that will help.  Thanks.

Dennis


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## jim18655 (Mar 20, 2015)

Any error codes?
How long of a run from the panel to the drive? How's the input voltage when the motor is under load? Did you set the maximum current output to match the motor?


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## atunguyd (Mar 20, 2015)

What is the torque rating of the motor. A vfd can't really improve the torque of a motor all that much and at speeds higher than 60hz you will suffer from reduced torque if the voltage is not increased with the frequency.


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## stupoty (Mar 20, 2015)

Is the motor expecting 220 volts? Low voltage to motor can cause less torque. Is their a 110v terminal layout for the motor?

Stuart


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## den-den (Mar 20, 2015)

There is a problem here somewhere, a 1hp motor should produce quite a bit of torque.  Does the drive trip on over-current when you stall the motor?  I agree that it would be wise to verify output voltage (check it at 60 hz).  Also if this motor can be wired for other voltages, verify it is wired correctly for 220/240.


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## Transformer (Mar 20, 2015)

Wow, South Africa, USA and England - what a brain trust to call upon!  So I shut off the VFD and went poking around in the electrical connections but could find nothing there.  So I turned everything back on thought and I would redo my hand breaking test, put the RPM at 600 and grabbed the bar.  Whereas previously I could easily stop rotation now I could not.  The only thing I can think of is that turning the VFD off and on allowed some change in the settings to take place.

Or............ I once took some electronic item in for repair and the fellow checked it out and pronounced it fit and functioning perfectly.  His diagnosis "It just wanted to go for a walk."

Thanks for the responses and turning my head away from the VFD settings.

Dennis


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## JimDawson (Mar 20, 2015)

In addition to the above comments, make sure the max output current is set to the motor nameplate value (P0.01)


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## Buzsaw (Mar 21, 2015)

There are 2 styles of drives variable torque and constant torque, constant torque is what is needed for a lathe. Constant torque is used in industry for conveyer belts as the load increases the drive will compensate for it. Variable torque drives are for fans pumps etc. where the loading stays the same. I have never set mine up on my constant torque drives but I know there are multiple parameters to set.


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## uncle harry (Mar 21, 2015)

Automation Direct has excellent phone accessable support staff who seem to be specifically oriented to their VFD product line. I have the same 120 vac input unit you have & they were clearly helpful diagnosing a minor difficulty that I had experienced.


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## jererp (Mar 21, 2015)

You stated that you have the motor pulley on the largest size. That mechanically reduces the torque at the spindle. Change your pulley arrangements to give you a 1:1 ratio. Then you will see the same torque at the spindle as you have at the motor.


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## CluelessNewB (Mar 21, 2015)

Everything you describe makes me think motor is wired for 440 rather than 220.


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## stupoty (Mar 21, 2015)

Ow hello, i just had a read of the manual, i hadn't realised they were voltage doubling vfd's 

Stuart


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## Jim Nunn (Mar 25, 2015)

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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## uncle harry (Mar 25, 2015)

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.
> 
> ...



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


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