Thread: vfd ....again

Any one have a link to 1ph to 3ph vsd with vector control (that is known to work)for 2hp motor?...at a good price!!!!

Its hard to tell if the hyangs or whatever they are called actually can do vector control

Originally Posted by eskimo

Any one have a link to 1ph to 3ph vsd with vector control (that is known to work)for 2hp motor?...at a good price!!!!

Its hard to tell if the hyangs or whatever they are called actually can do vector control

No they can't. You certainly would not expect a 2.2Kw VFD with vector control to sell for around $150. Probably 2x that amount, maybe a bit more. I don't know much about the VFD's with vector as I consider them outside my price range and I just upsize the motor by maybe 50% which minimises any lack of low rpm power/torque.

Simon

I have one of these vector control SAJ's on my Hercus MW lathe driving a 1HP motor and it works well enough on standard V/F operation that I still haven't bothered to investigate (or turn on) the Vector control capability.
I typically run it continuously between 25 and 100 Hz (and for short periods as low as 15Hz) and change pulleys for speeds outside this range

One of the reasons I haven't used the vector control is that the manual says that unless the motor has independent cooling capability continuous low speed vector control mode should not be used.

One day I will investigate this a bit further and see what it can do in terms of improved cooling

BTW here is a basic intro to what Vector control means
http://www.eng-tips.com/faqs.cfm?fid=1062

Besides low speed torque improvement the other reason for using a vector control VFD is for accurate (e.g. 0.1 Hz) speed control which is something that I (and I suspect most of us just running machinery) don't have a need for.

Thanks for the info Bob.

Another thing that needs to be realised if using a VFD on a lathe at slow speeds is that if your lathe has oil splash lubrication in the headstock, it's spindle bearings may not recieve enough oil.

Simon

Originally Posted by eskimo

Any one have a link to 1ph to 3ph vsd with vector control (that is known to work)for 2hp motor?...at a good price!!!!

Its hard to tell if the hyangs or whatever they are called actually can do vector control

I have 3 V/F VFD and 4 Vector VFD. Bare the first VFD 15 years ago, I bought them all from eBay, either new old stock or used for bench testing or simply used, and I never had to pay more than 30% of list price. No problem so far, all are still running fine. You need time though to get bargains. That is why I simply buy a good VFD if the price is irresistible, for future use. If you need a VFD right now, that obviously does not work well.

As for Vector drive, they are simply great for machine tools like lathe or mill. You get a useful speed range of 6:1, as opposed to 4:1 for V/F drives. For a manual hobbylathe or mill you simply need not worry about motor cooling at low speeds, its a non issue because these tools never run for hours at low speed like they potentially would in a factory. You regularly stop to take measurements or clear chips or the like. I never had a motor getting hot to touch, just warm. Besides that, every decent vector VFD calculates the motor temperature on the fly and would trip out if the calculated temperature is excessive. To calculate properly you have to tell the VFD if its a stock TEFC motor, or if it has an independant external fan, and what nameplate ratings it has. That said, if I had to pay full list price for a VFD, I would probably too stick to a V/F type if its only for home use.

I have two LG sensorless vector drives (Korean) that I purchased new from the Australian distributor about 12 years ago for approximately $400.00 each. I have enabled sensorless vector control on the drive on my vertical milling machine to help with starting on the highest speed, the other drive is on a 16 inch shaper and is running perfectly just with V/F control.

Last night I was thinking about a way of testing the Vector drive capability of the 2HP SAJ VFD I have on my lathe and I thought why not use my HP rig since it really measures torque.

Thing was I didn't really want to disconnect the SAJ and motor from the lathe and put the motor on the HP rig so I set the HP rig up on the bed of the lathe - the rig has nice rubber feet which fortuitously sit straddle the bed
I put one of my HP rig pulleys in the chuck and ran it like i did in my HP experiments. If anyone wants to see this I can post a photo

After mucking about with a few HP curves I realised I could get a goo indication of the difference by just measuring the torque at a specific RPM slip of the motor.

So, I set the VFD to a specific frequency, measured the unloaded RPM of the HP pulley, hoiked on the HP rig brake lever so as to reduce the pulley RPM by 10% and then directly measured the torque.
Repeat for other frequencies with and without vector drive enabled.

The following are the % differences in torque for 15, 20 and 25Hz between the V/F and Vector settings.
15 Hz : 33%
20 Hz : 29%
25 Hz : 30%

So the figures seems to be around 30% greater torque using the Vector settings.

If I get round to it I will see what happens at even lower frequencies.

Originally Posted by BobL

Last night I was thinking about a way of testing the Vector drive capability of the 2HP SAJ VFD I have on my lathe and I thought why not use my HP rig since it really measures torque.

Thing was I didn't really want to disconnect the SAJ and motor from the lathe and put the motor on the HP rig so I set the HP rig up on the bed of the lathe - the rig has nice rubber feet which fortuitously sit straddle the bed
I put one of my HP rig pulleys in the chuck and ran it like i did in my HP experiments. If anyone wants to see this I can post a photo

After mucking about with a few HP curves I realised I could get a goo indication of the difference by just measuring the torque at a specific RPM slip of the motor.

So, I set the VFD to a specific frequency, measured the unloaded RPM of the HP pulley, hoiked on the HP rig brake lever so as to reduce the pulley RPM by 10% and then directly measured the torque.
Repeat for other frequencies with and without vector drive enabled.

The following are the % differences in torque for 15, 20 and 25Hz between the V/F and Vector settings.
15 Hz : 33%
20 Hz : 29%
25 Hz : 30%

So the figures seems to be around 30% greater torque using the Vector settings.

If I get round to it I will see what happens at even lower frequencies.

Why did you not go down to 3Hz? It is at speeds BELOW 15Hz that you would really see the difference between a V/Hz and a vector drive. At speeds below say 12Hz, a V/Hz drive simply has no torque and runs erratic at the slightest load. Of course, before testing you should run the vector VFD's motor calibration routine.

Originally Posted by cba_melbourne

Why did you not go down to 3Hz? It is at speeds BELOW 15Hz that you would really see the difference between a V/Hz and a vector drive. At speeds below say 12Hz, a V/Hz drive simply has no torque and runs erratic at the slightest load. Of course, before testing you should run the vector VFD's motor calibration routine.

Will do.

Here are the results for the torque output by a Vector enabled VFD versus the same VFD/motor under simple V/F control.

The VFD has been auto-tuned to the motor to self optimise some of its parameters.

The torque figures shown are the torque generated when the motor RPM slips by 10% of the free running RPM.

The Vector enablement seems to generate nearly double the torque at low RPM than does the V'F control does.
Another way to look at this is; @ 10Hz, Vector enablement generates the same torque as about 25Hz does on V/F
In theory this means if your frequency range is nominally 25 - 100 Hz (4:1) it can then go from 10 to 100 Hz (or ~10:1)

At higher frequencies the differences in torque are reduced but there is still a substantial difference and well worth having.

Here was the setup for those that are interested.
The steel band between the hooks was engaged onto the pulley.

The LHS force meter is floating and can be lifted by the handbrake on the LHS of the frame.

The RPM is read by the taco clamped to the top of the frame.
The free running RPM at a specific frequency is noted.
A target RPM value 10% less than the free running RPM is calculated.
The hand brake is hoiked on until the calculated RPM is reached and a photo taken of all the displays
The final torque is the difference between the two weight measures ,times the radius of the pulley.

It's quite difficult to hit the target rpm exactly and sit on the target RPM until the torque stabilizes which is why the torque V RPM curves are not smooth.
I have discussed this on previous posts on HP measurements
If I can hit the target RPM exactly the torque measurements are highly reporducible.

Originally Posted by Stustoys

Bob!!! come back and fix your pictures.....

Done

Slow image uploads.

Dean

Bob, interesting results. Maybe you could get even bigger differences, if you tried to optimize the VFD to the motor. There are two steps. First there is the "automatic calibration" procedure, which measures the motor stator resistance. That is a good starting point. But then there are two parameters that can be very worthwile to adapt manually. These are not touched by the automatic calibration. And these may have slightly different names in the manuals of different makes/models of VFD's. But the two should be present on every sensorless vector VFD software:

- sensorless vector speed control loop gain - proportional term

You increase this value under nominal speed, until the motor becomes unstable when loaded. Then back this setting off by 10%

- sensorless vector speed control - integral term

The proportional term must be optimized first. Then you increase the integral term until thr first signs of instability occur, then back it off by about 30%.




What I have found, is that low speed torque alone is not the whole story. One has to look at the dynamic behaviour too. In my experience on lathe and mill, a V/Hz VFD becomes unstable at speeds below about 12Hz. What I mean is, if you take a cut at say 10Hz on a lathe mounted V/Hz VFD, the spindle rpm first drops, then after one or two seconds the VFD speeds up. Initially this looks like "rough running" and just tells you that you reached the limits. But as you try to go lower, say 8Hz it starts oscillating (or hunting) between well below 8Hz and above 20Hz. It is impossible to do any serious work under these conditions. My personal lower limit for a V/Hz drive on a lathe is 12Hz. It can run slower without getting unstable, but only for tasks like countersinking from the tailstock that need very very little torque.

With the vector drive, there is no instability or hunting down to 1.5Hz. That is a huge difference to the 12Hz of a V/Hz drive. And... I never measured it like you, but just by feel, I think at speeds of 5Hz or 3Hz or 1.5Hz, the difference in available and usable (not unstable) torque is in the order od magnitude of several 100%, not just 100% as your measurement seems to show.


What I have found when comparing a sensorless vector VFD to a V/Hz VFD, is that the Vector VFD definitely cover a much wider speed range. But it is also more demanding in setttig up and optimising parameters. One can set the integral and proportional terms too critical, then one may get exceptional and stable low speed performance, but at high speeds above 70Hz one may have an instable drive, one that increases rpm when loaded. This is not acceptable, even if it does not get unstable (hunting) one does not want an increase in rpm when loaded. It can take an hour or so to find the optimal settings that work well for all speed ranges. A V/Hz VFD is definitely much easier to set up.

As I said, I bought all my vector drives NOS or pre-owned at bargain prices. If I had to pay full list price, I would very seriosly consider if for the same money I could buy a 2 sizes larger HP motor woth V/Hz VFD to suit, and possibly get the same low speed toque. I guess everyone will have to make up his own mind about vector or V/Hz VFD. There is no one single answer to fit meveryones needs and wallet.

So here's a simple question.

If I want 1 HP available at say 10 Hz for a 4 pole 3 phase motor, what nameplate HP do I need to be buying? Assume I want a top end frequency of 100 Hz and ideally no less than 1 HP as well so in effect a 10:1 speed range with a minimum of 1 HP available at the extremes.

Don't care what sort of drive VFD drive for this question, but the vector drive is going to be the obvious choice for speed stability.

PDW

Originally Posted by PDW

So here's a simple question.

If I want 1 HP available at say 10 Hz for a 4 pole 3 phase motor, what nameplate HP do I need to be buying? Assume I want a top end frequency of 100 Hz and ideally no less than 1 HP as well so in effect a 10:1 speed range with a minimum of 1 HP available at the extremes.

Don't care what sort of drive VFD drive for this question, but the vector drive is going to be the obvious choice for speed stability.

PDW

With a vector VFD, you would need at least a 5HP motor and VFD, to get 1HP at 10Hz.
With a V/Hz VFD, you would need at least a 10HP motor and VFD, to get 1HP at 10Hz.

That is the reason most home users choose to keep their lathe or mill gearboxes.


PS: power is torque multiplied by rpm. VFD's are constant torque below 50Hz, and constant power above 50Hz.