VFD Can they run a motor at 1.5 Hz

# Thread: VFD Can they run a motor at 1.5 Hz

1. ## VFD Can they run a motor at 1.5 Hz

I have a Hermle WF3SA milling machine with the DC pancake motor destroyed beyond repair
Now I have a VFD (Lenze ESMD222X2TXA) and want to use that with a 1400RPM 50Hz 2.2Kw motor I have
Problem is the huge ratio between lowest and highest speed
The motor should run between 30 and 3000rpm resulting in about 2Hz to 210Hz
We hooked up the VFD but we could not get it under about 4 Hz We were thinking perhaps with a 10turn potmeter we could get better results
But anyway at the lowest speed the motor started to stutter Turned very irregulary
My question :
Is 1 Hz possible and what would it need

I also looked into a stepper motor but the 3000rpm seems to be a problem with these
Also a 2.2 Kw will not be cheap I suppose

Peter

2. You will have negligible torque available to do any work at extremely low frequencies, so even if you could get a stable 2 Hz, it would, IME, not be useful. What sort of work would you anticipate doing on a milling machine, where the spindle takes 2 seconds to go around once? If coarse pitch tapping, you are quite SOL, owing to no torque.

Regards.

Mike

3. You MIGHT be able to get it to go.... Look for a torque boost function, which is more common on VFDs that are intended for HVAC applications.

HOWEVER....

There is no reason to do that low speed, because the power available at that point is going to be very small, the motor will not do much useful work. Assuming that the torque (motor current) can be kept constant, then the power would be proportional to RPM, and that means something around 1/800 of the actual motor rated power will be available.

You would be far better advised to put in (if it is not already there) a belt or gear system to allow the motor to run faster at slow cutter speeds. (I assume this is a spindle motor).

4. No it is not a spindle motor Its a powerfeed motor
As far as I understood torque is constant on a VFD Thats what you need with powerfeed too
At the lowest setting I could get it had enough torque to function Only that was too fast and stutters then

It is a replacement for a DC motor and it fits in the same position
If I make a reduction(difficult BTW) the upper frequency goes up too Can I run that motor at 200Hz ??? at 5600RPM ???

Peter

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Originally Posted by Peter from Holland
I have a Hermle WF3SA milling machine with the DC pancake motor destroyed beyond repair
Now I have a VFD (Lenze ESMD222X2TXA) and want to use that with a 1400RPM 50Hz 2.2Kw motor I have
Problem is the huge ratio between lowest and highest speed
The motor should run between 30 and 3000rpm resulting in about 2Hz to 210Hz
We hooked up the VFD but we could not get it under about 4 Hz We were thinking perhaps with a 10turn potmeter we could get better results
But anyway at the lowest speed the motor started to stutter Turned very irregulary
My question :
Is 1 Hz possible and what would it need

I also looked into a stepper motor but the 3000rpm seems to be a problem with these
Also a 2.2 Kw will not be cheap I suppose

Peter
I had that exact problem a couple of times. The only good solution I found was a NEMA42 stepper motor and drive and a VFC110 based oscillator. The oscillator sends pulses to the drive, drive moves the motor. You have full torque from standstill - it's the nature of steppers. And you can do one revolution per hour should you need.. The VFC110 oscillator is easy to make - just a couple of compenents and a pot to adjust the frequency. A NEMA42 stepper has COLOSSAL torque. Here's an example :

1PC Nema42HS946 Stepper Motor 177oz-in=12.5N.m 5.5A CNC machine 2 phase | eBay

Look for a 2-3 stack NEMA42 with an under 5A current - makes the drive much cheaper.

The max rpm you'll get from the stepper is around 1200 and ( !) depending on the quality of the drive you will get some resonance at certain speeds. I did not find that to be an issue.

6. Yes but not the max rpm that I need
And if I put a transmission in between I need a motor with 2.5 times the torque Thats once more €€€€€

Perhaps I better find another DC motor
The driver thats in the milling machine might be still oke
I need a 170volts 2,2kw 3000rpm

Peter

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Should be easy piece of cake with one of the better vfd's

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Originally Posted by Peter from Holland
Yes but not the max rpm that I need
And if I put a transmission in between I need a motor with 2.5 times the torque Thats once more €€€€€

Perhaps I better find another DC motor
The driver thats in the milling machine might be still oke
I need a 170volts 2,2kw 3000rpm

Peter
Peter, are you sure you need that much speed on the feeds ??

9. Yes we need that 3000rpm to meet the technical data for this machine
Thats for the rapids

Peter

10. Originally Posted by MattiJ
Should be easy piece of cake with one of the better vfd's

Lenze is a good brand This VFD I bought about 10 years ago new and never used it
My guts tell me a puls generator could help to reduce the stuttering
Am I right ???

Peter

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Originally Posted by Peter from Holland
Lenze is a good brand This VFD I bought about 10 years ago new and never used it
My guts tell me a puls generator could help to reduce the stuttering
Am I right ???

Peter
pulse generator/tachometer might do the trick or upgrading to sumthing like ABB ACS800 series with direct torque control (DTC). Not 100% sure how low speed the you could get with the DTC drives without feedback, afaik around 1-2hz. And with feedback full torque down to zero speed.
ABB's DTC drives biggest negative is probably the price.

12. Originally Posted by MattiJ
pulse generator/tachometer might do the trick or upgrading to sumthing like ABB ACS800 series with direct torque control (DTC). Not 100% sure how low speed the you could get with the DTC drives without feedback, afaik around 1-2hz. And with feedback full torque down to zero speed.
ABB's DTC drives biggest negative is probably the price.
Can you tell me if this one will do the trick ???
https://www.marktplaats.nl/a/hobby-en-vrije-tijd/elektronica-componenten/m1194035333-abb-frequentieregelaar-3kw.html?c=8c285449651fa109c354bbabe740c1b&previou sPage=lr&pos=24

Peter

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It's very difficult to tell if it'll do the trick w/o reading the manual and actually trying. I have around 12 VFD's and NONE will go down that low with any significant torque. The problem you are having is very common with Maho milling machines and the solution I gave you works. But Maho has a 2nd motor for the rapids. I'd then use a gearbox and run the motor at 6000 rpm for the rapids. The very fancy VFD's can run brushless servos and a couple of other motor types. Pain to set up but might be worth the trouble. Check Omron ones.

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Originally Posted by Peter from Holland
Can you tell me if this one will do the trick ???
AFAIK it should do.

15. Originally Posted by MattiJ
AFAIK it should do.
For that price I better buy it then

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I have used a Hitachi SJ200 drive to run an 1800 rpm motor at 18 rpm less than 1hz using sensorless vector mode. I was driving a piston pump through a worm gear reducer where the load varied as the pump crank stroked. I used a 2 hp motor instead of the 1/2 hp the pump was rated for to keep the torque up. The wj200 can also use a tachometer to provide even better speed regulation.

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Originally Posted by Peter from Holland
replacement for a DC motor
Nothing at all wrong with your command of the English language Peter, but if that has to be direct-drive, armature at 1:1 with load, what you just described is an "oxymoron". AKA a contradiction in terms.

UNLESS.. you can use an AC motor with a SERIOUSLY high pole-count.

And/or AC "Torque motor" construction. EG: Hold that torque indefinitely at stalled rotor, no fuss, no drama. Closers for common lift doors the example encountered daily, but seldom seen. Variac or even just a healthy Rheostat was all they needed added for flexibility. Line frequency the whole time.

VFD'ed 24 pole would be a good start if you have to work at low, or even fractional RPM in direct-drive, 12 pole "maybe", 8 pole not likely even with the VFD's help.

"Set your sights higher!" Ceiling fan motors tell that tale. As do Servos. Not new.

Cheap as AC+VFD or Servos have become, when you still encounter Dee Cee at all, there is usually a very good reason it is where it is.

Some earlier "pioneer" trying what you are trying simply got fewer Apache arrows in his arse with DC than AC.

18. Originally Posted by garyhlucas
I have used a Hitachi SJ200 drive to run an 1800 rpm motor at 18 rpm less than 1hz using sensorless vector mode. I was driving a piston pump through a worm gear reducer where the load varied as the pump crank stroked. I used a 2 hp motor instead of the 1/2 hp the pump was rated for to keep the torque up. The wj200 can also use a tachometer to provide even better speed regulation.
Did it turn smoothly at 1Hz or did it stutter I would imagen you could see the rotor jump from one magnetic field to the other every second
Peter

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Originally Posted by Peter from Holland
Did it turn smoothly at 1Hz or did it stutter I would imagen you could see the rotor jump from one magnetic field to the other every second
Peter
Well 3-Phases splitting that 1 Hz, bit of a helix twisted-in already as well to smooth transitions in any case, so not as bad as a LEDEX rotary solenoid at least! Nor as powerful.

DC motor would need foresight of type choice as well. 10EE's sacrifices efficiency (low 70%) with four poles PLUS four inter-poles, four brushes rather than two, and a winding interleave that smooths the hand-off to very much finer granularity, if you will, than "ordinary" DC motors.

That old 10EE motor would also cost about as much as an entire new lathe, if not more, South Korea or Taiwan's Mori-clones as a yardstick. Comparable 'vanilla', not even Type T, Reliance DC start at over \$11,000 anyway, per their website.

Challenge you described sounds like servo turf, not ordinary motors, either AC or DC.

Or an electrically shifted planetary gearset?

Or TWO motors? One for creep, the other for slew? That might be less-costly than gears, not hard to select electrically in CNC, or by handwheel switch or sensor. Each motor then optimized for its work.

Might share a common output shaft, 'stacked'?

And.. Per Lybarger's Corollary, there isn't any b****y SPACE yah?

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Originally Posted by AlexO
The very fancy VFD's can run brushless servos and a couple of other motor types. Pain to set up but might be worth the trouble. Check Omron ones.
I'd classify ABB's DTC drives pretty much to "very fancy" category. Close to AC servo performance with induction motor. And besides it seems to be made in correct country

On trade shows they used to have big motor with half meter lever directly on the shaft and you could try arm-wrestling with that "thing". Position hold at zero speed and full torque.