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VFD question dealing with Hz

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ridgeway

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#1
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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JCByrd24

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#2
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.
 

markba633csi

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#3
It's most likely a programming issue since it sounds like it's basically working - review the manual again
Mark
 

radial1951

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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...
 

ridgeway

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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.
 

radial1951

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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!
 

ridgeway

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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?
 

Dave Paine

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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.
 

radial1951

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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...
 

CluelessNewB

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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.
 

ridgeway

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Here is the tag on motor. I got the 2.3 there...not sure if that is right or not.
Thanks for all the info...I have a better understanding what is going on with a VFD.

All I can say....I should have done it years ago, lol. The machine is so smooth and seems like it makes a better finish due to no vibes going through the tooling. If I ever get another lathe...3PH and VFD will be a necessity!
 

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cdhknives

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#12
575 volt motor...your VFD should be set for that max voltage output accordingly. What is your input voltage/phase/circuit breaker size? Your input may not be able to supply enough power to handle the inrush of a rapid speed increase.
 

CluelessNewB

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It's a 575 Volt motor. You didn't say what model FM50 you have or what your input voltage to the VFD is. I'm guessing its an FM50-202 which is a 230V In --- 230V Out. I will be very surprised if that works out well under load. FM50-202.PNG
 

radial1951

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Curious... What is your single phase voltage to the VFD? The plate on the motor says 3ph 575volt. Do you have it wired via the DELTA or STAR connections in the motor's junction box?
Also, what brand are those green link belts on your lathe?
 

radial1951

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LOL, we all noticed the 575volts! That doesn't appear to be a dual voltage motor ie Star/Delta connections. Your VFD max 3ph output volts = input volts. If your 1ph supply is 230v then the correct nominal Hz should be set to 230/575x60 = 24Hz. Which gives 0.4 of the full voltage output of the motor. IF THE ABOVE is the case, no wonder it doesn't like quick speed changes even with the lathe just running no load. At the VERY best you only have 0.8HP available at 698rpm.
You will find, from the above, that as long as the correct V/Hz ratio for the particular motor (Delta or Star connected) is maintained, a 3ph motor will run happily at the proportional rpm and power output. Amongst others, I have a 3ph 415v 50Hz 1425rpm motor running with a Chinese AskPower VFD at a nominal setting of 240v/29Hz on a drilling machine (ie 240/415x50=29Hz). In my case the output is theoretically 0.58 of the motor's rpm and power at 415v/50Hz. It happily runs up to 60+Hz for drilling small holes and if needed I could move a belt to gain torque for bigger holes(never have).
Your motor may be inverter rated, but it appears it is for a supply of 3ph 575v... :(

Regards, RossG.
 

ridgeway

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The belts are harbor freight. I guess that is why the motor was cheap, lol. Looks like I will be motor shopping since I can't supply more than 240 v....
 

markba633csi

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Always check the motor specs before you part with your hard-earned cash :)
 

ridgeway

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Always check the motor specs before you part with your hard-earned cash :)
I saw the 575, I thought that might be max volts and never gave it much thought. LOL...I said I wasn't an electrician!

Would it damage the VFD or motor if I use it till I get another motor?
 

CluelessNewB

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Yes that Surplus Center motor should work assuming frame size and shaft size are ok. It's above my pay grade to answer question about damaging motor or VFD.
 

cdhknives

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You could also put a transformer between the VFD and motor to step up from 230 to 575V. More cost and another device in the system, but probably (slightly) cheaper than a motor. So long as your VFD can handle the motor's kVA (volts*amps) it should work.
 

ridgeway

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You could also put a transformer between the VFD and motor to step up from 230 to 575V. More cost and another device in the system, but probably (slightly) cheaper than a motor. So long as your VFD can handle the motor's kVA (volts*amps) it should work.
The VFD can't handle that much voltage. I will get a new motor and try and Craigslist this motor.
 

cdhknives

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The VFD would only see its 230V max, the transformer and motor would be the only things to see the 575...3 phase 208 to 575 transformers are available. The VFD can output sufficient power (volt amps, VA), just not at high enough voltage to push max amps though the motor windings. Voila instant derating of HP in the motor. You trade volts for amps via a transformer. It WILL work, but MAY NOT be the cheapest alternative. Choose a 3 phase 208/230V to 575 transformer of the same or larger kVA as the VFD/motor, wire the output of the VFD to the line/input of the transformer, and wire the motor to the output/.load side of the transformer. This happens in my world (petrochemical instrument/electrical) all the time as 480V generators are widely available but when we have to power down a 2400V or 4160V motor control center and keep a pump running, we have to put a transformer between the 480V generator and the 4160 pump motor. Transformers don't care about frequency so long as there is some (they don't work on DC) as they pass frequency straight through. Again, it will work, but might not be the cheapest alternative. Shop around and see...
 

markba633csi

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I wouldn't go the transformer route- It works in theory but it's less efficient and usually too costly. And they weigh a ton.
You should be OK using the 575 till you get another motor
Mark
 

JimDawson

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From what I have heard VFDs and transformers on the output side don't play well together. Better to install a motor with the correct voltage then life will be good. :)
 

ridgeway

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So what is inside the motor that requires the 575 volts? Why is it working on 220v? I've used the lathe several times, but haven't hogged anything yet? I'm guessing under a heavy load, it will bog down?
 

Eddyde

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The windings, it's built for that voltage, no way to change it. Its running but probably at less than half power. Get the motor you posted, it should work fine.
 

cdhknives

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Jim, transformers on the output side of VFDs can get tricky but are commonly done. For a 2 Hp motor likely the only issue would be limits on how low of speed it could be run. Most of what I (and industry in general) see are hundreds (thousands) of Hp motors for pumps and such. Harmonics, load balancing, impedence matching, etc. become issues fast in this world and that is probably the source of the 'don't do it' conventional wisdom. If the OP has easy access (like they did the motor) to such a transformer, it is worth a shot. If they have to buy one new, a new motor makes more sense. I just offer an alternative to pursue if it makes sense to the particular application...a new motor is certainly a very good option here, as is a different VFD that will take multiple input V and output 575V 3 phase.
 

ridgeway

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Curious... What is your single phase voltage to the VFD? The plate on the motor says 3ph 575volt. Do you have it wired via the DELTA or STAR connections in the motor's junction box?
Also, what brand are those green link belts on your lathe?
Again on the belts...they work well. Although they are Harbor Freight, I believe they are made in the USA.
 
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