VFD question dealing with Hz

ridgeway

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I converted my Grizzly 4003 with a Teco FM50 and Lesson 2HP 3PH motor. All works great. Wired up VFD control side to factory apron switch, estop, inch and added a pot dial.

I set my max Hz level to 75 for a little extra speed when needed.

The Lesson is an inverter duty motor.

My question is when I turn the pot dial up fast from 60 hz or below to 75hz, the motor slows down. If I turn the dial slowly from 60 to 75, it ramps up the speed and maintains speed.

I'm guessing it's the way the VFD works or it's the cheap pot dial. Just wondering, I'm no electrician, lol.

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My cheaper Chinese VFD doesn’t do that. I’ve got mine set for 20-90hz. My VFD is set to display Hz, and yours likely is too or can be. This setting will show regardless of whether the motor is running or not, so you should be able to adjust your POT without the motor running to see whether the VFD is commanding this behavior or reacting in some way only when the motor is running.
 
Not likely to be the pot, it just sends a signal to the VFD. It may have something to do with the acceleration time setting. Or it may be overloading the VFD as it tries to rapidly increase the motor speed. Put the lathe in the slowest gear setting ie lowest load, and see if it still does it. Might give a clue as to what is happening...
 
I tried it in a lower gear and did not do it. The manual isn't very detailed in explaining each function. There is a V/F pattern setting and I have it set for "high starting torque". There is another function that is named "torque compensation gain" = 0-10%. It is set on zero, which is default. The manual does not explain much about them, lol. Not sure what "carrier frequency" is either. Factory setting is 8 kHz.
 
Ok, so it's not the pot and the motor is ok. So it seems the VFD doesn't like a sudden increase in load when already running the motor. High starting torque is not usually needed for small machine tools as there is not a lot of inertia to overcome and the load occurs at operating speed when taking a cut. I'm not familiar with your VFD but maybe changing the Voltage/Frequency "pattern" to move the "torque band" up the rpm range may help. This may need the acceleration time increased to let it spool up over several seconds. Does the VFD have a high enough rating to handle the HP of the motor under max load? User manuals for VFDs are notoriously inadequate!
 
The VFD is adequate for the motor and amp draw. It's 2HP rated and the motor is 2HP. Amp rating on VFD is 7.5 and motor is rated at 2.3 amps.

I will experiment a little bit with the programming. I do know I set a slower startup in seconds. I think I'm at 3 or 4 seconds. It would not handle anything from faster than that, lol. It didn't like a 1 second startup...

So you are thinking of switching back the V/F pattern to normal than a high torque setting? What is V/F anyhow?
 
So you are thinking of switching back the V/F pattern to normal than a high torque setting? What is V/F anyhow?

V/F is likely Volts / Frequency, normally stated as V/Hz. The VFD controls the output voltage to the motor proportional to the Hz setting.
 
David is correct it's Voltage/Frequency Ratio. Let's say your input to the VFD is 240v and you have all parameters correctly set for your motor. If your motor is connected for 1440rpm @ 240v (3ph 50Hz) and you change to 25Hz, the VFD will drop the output to 120v to maintain the V/Hz ratio. Clever VFDs ($) will maintain torque down to quite low Hz. But be careful of overheating under load if it is a fan cooled motor as air flow is reduced considerably at low rpm. If you go over the rated Hz the motor will run faster but the torque won't increase as the voltage is limited to your max input of 240v. I often run 50/60Hz motors at 80-100Hz no (apparent!) problem. Make sure you set the upper Hz limit to say 100Hz as some VFDs factory setting is 400Hz!!
Under normal running your 2HP VFD is ok for a 2HP motor but the starting current is probably way over 2.3A which is why the VFD needs several seconds to ramp up to motor speed depending on the lathe's speed setting. It would be different if the lathe had a clutch. My VFDs are over-rated at least 50% of motor HP.
I'm no electrician either, had to learn the hard way, just like you are now :) Please be careful...
 
The VFD is adequate for the motor and amp draw. It's 2HP rated and the motor is 2HP. Amp rating on VFD is 7.5 and motor is rated at 2.3 amps.


If it's a 2HP motor 2.3 amps sounds wrong, is that maybe the rating at 460V? (Even then it seems a bit low for a 2HP motor). If I remember correctly the FM50 doesn't have any parameter to set for "motor rated current" so I don't think this has anything to do with your problem.
 
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