# Motor on VFD "stuttering"



## telsa (May 22, 2015)

It's in the fluid physics of the cream.

You'll see the same dynamics with the ink that goes into ball point pens.

Its viscosity swings wildly with pressure.

All that is necessary is that the goop get slightly off-spec to see the matter intensify.

As for the VFD, it would seem that it's 'hunting' for the right torque feed-back.

It takes BOTH factors to produce the stutter-step shudder.

I'd dump the Automation Direct puppy and get the steadier logic that's up to the conditions required.


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## ponyboy (Nov 18, 2012)

Is there a current limiting parameter? Not to be confused with the overload parameter. If you're exceeding the current limiting value you will only get a bum out of the motor. This happened to us on some spinout fixtures when engineering added a couple hundred pounds to a part without telling us, the motors were still strong enough for the job but the current limit parameter was too low now.


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## John Valdes (May 17, 2007)

Sounds like this process could use a Torque control drive or a closed loop ysytem that will react to change in load.
A simple Volts/Hertz control cannot maintain a certain speed if the load is to great.

Example. Conveyor carrying 100Lb boxes. Then they go to 300lb boxes. This conveyor is going to slow down or the drive may trip out on overload. 
This is surely a torque issue and the first indication was the setting you found. 

My suggestion is to go to a control that can produce full torque at low RPM, or use mechanical means (gear box) to allow you to run the motor faster than you are now.
Or if your control will accept a feedback signal and is capable of responding to load changes you could very well not have to work on it anymore. 

Just be certain you employ a drive that will respond to load changes. A simple volts/Hz control cannot do that.


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## Vintage Sounds (Oct 23, 2009)

telsa said:


> It's in the fluid physics of the cream.
> 
> You'll see the same dynamics with the ink that goes into ball point pens.
> 
> ...


I'd love to get a more sophisticated drive in there, but I'm just the new guy, and have very little influence on what they buy. I suppose if they want to pay me to sit there and poke around with my meter unproductively, they can.



Biscuits said:


> Is there a current limiting parameter? Not to be confused with the overload parameter. If you're exceeding the current limiting value you will only get a bum out of the motor. This happened to us on some spinout fixtures when engineering added a couple hundred pounds to a part without telling us, the motors were still strong enough for the job but the current limit parameter was too low now.


 I checked for that, but there wasn't one. The V/Hz profile seemed to be the closest thing there was to a proper current limit. If set to centrifugal fan/pump like it was, it would, according to the graph in the manual, starve the motor at low RPM.



John Valdes said:


> Sounds like this process could use a Torque control drive or a closed loop ysytem that will react to change in load.
> A simple Volts/Hertz control cannot maintain a certain speed if the load is to great.
> 
> Example. Conveyor carrying 100Lb boxes. Then they go to 300lb boxes. This conveyor is going to slow down or the drive may trip out on overload.
> ...


I think you're right, but I'll have to make a pretty convincing case to get them to think about it. There is a gearbox already, and there is even a sensor there which gives the operator an RPM readout, but this signal isn't used for any actual process feedback and they often don't even bother connecting it. I gather it would cost a few bucks to convert to closed loop control and the drives which provide it are a lot higher end than the dispose-a-drives we currently have. I only just transitioned to plant life and these are uncharted waters for me.


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## JRaef (Mar 23, 2009)

So your assessment is dead on, the Pump/Fan setting was totally inappropriate for that machine and the settings you changed to are what you should have done given that you have a cheap low functioning drive. Bravo.

If you do end up with issues still, you probably don't need to go with a full-tilt Flux Vector Control with an encoder feedback, you can likely use what's called "Sensorless Vector Control" (SVC). There are lots of inexpensive drives on the market now that offer SVC, some better than others, but all better than what you have now and the premium you will pay for that is likely a lot less than you think it is. 

This by the way is the consequence of shopping by price alone, which is the only thing AutomationDestruct has to offer.


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## oliquir (Jan 13, 2011)

the gs2 drive wont get into overload on slow rpm command, they will just get the motor humming and get warm. if you need cheap svc you can still go with AD gs3 series, they are basically delta rebranded vfds


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## Peewee0413 (Oct 18, 2012)

We have had issues with PD pumps stalling at low speed.. Come to find out the company went with the smallest hp motor and gearbox hitting the minimal torque requirements of the pump. All is good when the product was thin.. Put a viscous product in and they had me troubleshooting nothing.


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