VFD frequency range?

Aaron_W

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I've dug through a bunch of the posts here but not found what I'm looking for.

I'm finally getting the VFD set up on my mill, seems to be going well so far. One thing I'm not clear on is setting the frequency range for this use.

Clausing 8520, so belt drive, with pulleys used to adjust speed, 3 front, 3 back, so 9 speeds? VFD will be used to provide variable speed within those speed ranges.
3/4hp 230v 3 phase Dayton motor
Fuji Frenic Mini 2HP VFD FRN0010C2S-7U

Frequency is controlled through a potentiometer with a default of 0-60Hz. It looks like it can be set to run up to 400Hz (assuming that would be great for making smoke with my mill).

So my actual question:
What would a typical range be on a milling machine? Will too low of Hz hurt anything or just reduce power?


The manual is about 1/2" thick so a bit overwhelming taken as a whole, but the actual instructions are not too bad once I figure out which bits apply to me.
 

catsparadise

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I set up the VFD on my mill to generate 50Hz max (UK, so thats our default) and half that minimum. The VFDs usually drop the voltage as the frequency reduces so you'll lose torque at lower speeds, when normally you need it. Also with the motor running slow, any cooling fan on the spindle will not generate as much airflow and you risk cooking the motor.

Rob
 

mksj

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You loose Hp in a linear fashion below the base speed (60Hz for US motors) and you loose toque in a non-linear fashion above the base speed. As you slow the VFD, you also loose the mechanical advantage of the pulley ratio. If it is a newish Dayton motor (4 pole 1750 RPM) then the upper speed range is probably 80-90Hz and older motor then probably 60-75Hz. Anything above 90 Hz on an non-inverter motor the Hp will also start to fall off. Motors are also rated for what is known as constant torque range, older motors this is 2:1 (30-60 Hz, newer motors 4:1 (15-60 Hz), inverter motors 10-1000:1 (6/.6 to 60 Hz). My recommendations, in particular with such a small motor is 30-80Hz for a newish motor. There are a number of motor parameters that need to be set for the specific motor, it will also benefit from autotune which gives better motor performance. This is usually done statically if the motor cannot be disconnected from the mechanical drive, or dynamically with the motor drive disconnected. FYI, if you want to use the VFD over a wider operating range then you need to oversize the motor, so you would want a replacement motor ideally in the 1.5-2Hp range.

Most mill motors have a mechanical fan, so cooling suffers below 15-20Hz, and conversely are not designed to operate at 400Hz.
 

Aaron_W

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Disclaimer electrical is not my strong suit, in fact I was watching a video for installing a VFD and it took me a good 2 minutes to realize it was in Hindi, not English...


Anyway I did not realize there were so many variables to consider, here is a photo of the tag. It is actually a Baldor, the Dayton is on the horizontal mill, projects are bluring together. :rolleyes: Not sure the age, but it looks like it is an inverter motor?

Baldor 75hp.jpg
 

mksj

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It is an inverter only motor, it is not designed to be used without a VFD. The IDMN Baldor series are excellent inverter/vector motors, I used one on my last lathe. So the motor is rated to deliver full Hp up to 6000 RPM (200Hz), and they maintain constant torque almost down to 0 RPM. Typically you would change the pulley ratios to optimize the use with the higher RPM speed of the motor. Just beware the limitations of the mill drive and bearings. In this application you could easily operate the motor in the 20-120 Hz range, limiting the top drive speed to the rated safe spindle speed. The motor is a TENV, so no fan and less limitations with regard to cooling at speed extremes. If you had a higher Hp motor, you could use a higher RPM rating and use only 2-3 mill pulley speeds. Manual factory installed inverter mills typically use a 3 Hp inverter motor and operate it from 20-200Hz, and only use the back gear to cover the low speed range (~40-400 RPM).

You need to set the motor parameters in the VFD, you want to also make sure you are running sensorless vector control to optimize the motor performance across the operating speed range.
 

Aaron_W

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It is an inverter only motor, it is not designed to be used without a VFD. The IDMN Baldor series are excellent inverter/vector motors, I used one on my last lathe. So the motor is rated to deliver full Hp up to 6000 RPM (200Hz), and they maintain constant torque almost down to 0 RPM. Typically you would change the pulley ratios to optimize the use with the higher RPM speed of the motor. Just beware the limitations of the mill drive and bearings. In this application you could easily operate the motor in the 20-120 Hz range, limiting the top drive speed to the rated safe spindle speed. The motor is a TENV, so no fan and less limitations with regard to cooling at speed extremes. If you had a higher Hp motor, you could use a higher RPM rating and use only 2-3 mill pulley speeds. Manual factory installed inverter mills typically use a 3 Hp inverter motor and operate it from 20-200Hz, and only use the back gear to cover the low speed range (~40-400 RPM).

You need to set the motor parameters in the VFD, you want to also make sure you are running sensorless vector control to optimize the motor performance across the operating speed range.
I've gotten as far as the basic settings, which wasn't too difficult once I sorted out where to be looking. I'm moving into the "tuning" section which is more complicated. I don't want to blow up the mill before I get to play with it.

The VFD instructions are actually pretty good as far as how to set things but don't address the specific end use. I bought the VFD from Wolf Automation and my limited experience so far with their tech support has been good, but again didn't want to rely on someone who knew the VFD but perhaps not about mills. I think I can probably get things figured out from here, but know where to ask if I run into anymore road blocks.

My intent was to use the pulleys for gross speed ranges and then fine tune the speed with the VFD. It sounds as if I can do better than just fine tune it. The prior owner converted the mill to 3 phase / VFD from a 120v motor. Knowing how meticulous he is with his tools I am not surprised that he picked out a good motor for that use.

Thank you :encourage:
 
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