CMG Motors

[GSRocket]

Do the CMG variable speed motors from H&F come with controllers?
Also, do you think these Australian made motors are notably better than
the Chinese motors?.
With thanks.

[cba_melbourne]

Do the CMG variable speed motors from H&F come with controllers?
Also, do you think these Australian made motors are notably better than
the Chinese motors?.
With thanks.

It may be not what you wan to hear, but when I bought a 1HP 3phase CMG motor for my Waldown drill press about 5 years ago, the owner of the shop I bought it from said they are made in China except the 10HP+ ones.

Be careful with the motors from H&F with inbuilt speed controller. The speed range is very limited (600-1800rpm), suggesting very low torque at lower speeds. I suspect these are internally only single phase motors. More suited for fan applications, where very little torque is required at lower speeds. At first look these CMG motor with inbuilt speed control look very convenient. But for the asking price of $649 for such a 1HP motor, you can easily buy a 3 phase motor with a real single phase input VFD, giving you a far greater speed range and many many extra features such as braking. The downside is that you will spend some time to study the user manual....Chris

[GSRocket]

Thanks cba.
So a 3 phase with VFD will work on single phase out put?

[Greg Q]

Yes, up to point. 2.2 kw is about the limit of affordable single phase input VFDs. Also: using a VFD with single phase input yields a 240v three phase output (not 415). So you'll need a motor that is already dual voltage or have a rewinder fetch out the star windings to enable running on 240v three phase. Many motors in the 2.2 kw and under are so wired.

Greg

[GSRocket]

Thanks Greg.
I am thinking of 1.5k 3 phase with a VFD.
Which brands of motors are considered to be better?
And what controllers are considered to be good brands?
Thanks

[Greg Q]

I'm afraid that I don't know who makes good motors...I have always bought used for cheap on ebay. I seem to have a few WEG motors for one reason or amother.

As far as VFDs go: you can buy cheap ones on ebay out of China which seem to fairly common on this forum. i have one but have only used it for about an hour so cannot speak to its longevity.

If I was spending someone else's money I'd buy SEW Eurodrive or Danfoss. I have a small AC Tech on my drill press which I like very well too.

I have purchased from Marshall Automation in the states but there may be cheaper dealers.

Greg

[cba_melbourne]

> Which brands of motors are considered to be better?

Electric 3-phase motors are a very low tech commodity. Regardless where made or what brand, you should get what you pay for. If you are after something better, look on the nameplate what isolation class it is. The higher the letter, the better the wire insulation,meaning the hotter can the motor run and the longer will it last, and of course the more will it cost. If you want/need top quality, go for a VFD rated motor --- but note a non VFD rated will run just fine on a VFD, and will likely last for several 10,000 hours. Do not believe sellers that say you must buy a VFD rated motor, unless of course if you need it for a mission critical application or you need it to run for 8 years day and night nonstop.


> And what controllers are considered to be good brands?

There are many more VFD controller brands, than there are makers of IGBT transistor arrays. The best VFD's are those few that manufacture their own IGBT's. Think Hitachi, Siemens, Mitsubishi etc etc. But I guess any well known big brand is a good VFD.

What I recommend you do: once you consider a certain brand and model, google to find if you can download from the manufacturer website the user manual and the installation manual and some application notes. If you cannot download these easily and for free, FORGET IT run away and search for another brand!!!

Next read the downloaded user manual: some VFD's can be difficult to program, some others are real easy. Some have just two buttons and a hexadecimal display, which can make inputting your settings a very slow and unpleasant affair. The better ones have a small keypad and a better display. The best ones have a removable display/keypad that you can install in a more convenient place.

If you have the choice for the same price betweeen a V/Hz technology VFD, and a sensorless Vector VFD, choose the latter. V/Hz is obsolete technology, chances are someone wants to sell you his old stock. A V/Hz drive of a given HP rating should cost less than half the price of a Vector drive, otherwise you are wasting your money. Chris

[eskimo]

Fasco, ABB (asea) CMG, WEG and Teco will give you good service. All readily available

not in any order of preference

[eskimo]

> but note a non VFD rated will run just fine on a VFD, and will likely last for several 10,000 hours. Do not believe sellers that say you must buy a VFD rated motor,



within reason...I wouldnt expect any standard motor to last very long; in fact its life will be very short if working much above 80-100HZ ...below this would be okay

if one is expecting very high speeds of their motor/VFD then they should use a motor manufactured spefically for high frequency drives.

[jhovel]

Hi Eskimo,
could you eleborate why you said 'ordinary' motors wouldn't last long?
I can imagine the bearings may be less than optimal for higher speeds - but most motor bearings are rated double or triple or even higher than motor speeds.
I've been running a 1930's motor in my mill at 120Hz or so for long a time now.
None of my motors will run much above 120Hz - after that they seem to slow down rather than speed up. I guess the ciols can't recover that quickly.
How are VFD motors different?
Cheers,
Joe

[cba_melbourne]

within reason...I wouldnt expect any standard motor to last very long; in fact its life will be very short if working much above 80-100HZ ...below this would be okay

if one is expecting very high speeds of their motor/VFD then they should use a motor manufactured spefically for high frequency drives.


You must mean because of the rotor centrifugal forces? That is indeed an issue if using a two pole motor, because when driven at 100Hz this motor would spin at twice its nominal speed, eg 6000rpm instead of 3000rpm. That can become a safety issue. But if using a 4 (or 6) pole motor it is irrelevant; this is so because all makers of low HP motors use the same components like rotors to make different motors in their range. It saves having to make too many different parts. And it means all rotors are designed and balanced for 3,600rpm (which is the 60Hz speed) even those used in motors that only turn at 1,500 or 1,000rpm.


Trying to list the differences between a standard run of the mill motor and a VFD rated motor, these are the items I can possibly think of:

- a VFD rated motor will use a higher temperature wire for the stator, say insulation class F or G instead of C
- a VFD rated motor would have the entire stator carefully vacuum impregnated, or even cast in resin. This to avoid audible noise, and wire fatigue breakage caused by higher frequency vibrations.
- a VFD motor will either come with a completely independent cooling fan (like a box fan), or the shaft mounted fan is designed differently. The problem is that a motor driven under load at low speeds is not getting enough cooling air from a standard shaft mounted fan, causing it to overheat. And a conventional fan spun at 2x or more its design speed can be noisy like a vacuum cleaner and wastes power for nothing.
- a VFD motor will have some sort of carbon brush or slip spring to ground the rotor to the stator frame. This is necessary because of eddy currents generated in the rotor that flow to the frame. If these currents flow through the bearing balls the races get scored and the bearing fails prematurely.
- a VFD rated motor will be made with more and thinner iron sheets of different magnetic properties, to reduce losses at higher frequencies. In my experience, a standard motor used say for a lathe or milling machine spindle drive, will quickly loose power when driven above 100Hz, and barely kan keep itself and the spindle running above some 120Hz - no power left to make a cut. A VFD rated motor will be more efficient and remain usable up to 150 Hz . Special VFD rated motors can be designed to work at 1000Hz or more. Of course, the higher the frequency the more it will cost for any given power. High frequency spindle motors may also need water cooling because of losses and friction in the bearings.
- finally, you can expect the rotor of a VFD rated motor to be better balanced for less vibrations at higher speeds.

I personally have been running standard motors as sold in Australia by the brands of AEG/Lafert (Italian made) and CMG (China made) and Leeson (do not remember where made) with VFD's. The oldest is now 10 years old. Cannot complain for a motor that was under $ 120 new and with warranty from a Melbourne dealer. The cheapest VFD rated motor back then was a Baldor (US made) for some $ 600. For the difference I could have bought a new motor every 2 years. But I still use the first one. I would worry if it was for a mission critical use, but for a machine tool? Or look at it this way, lots of tools one can buy for the price difference. Chris

[jhovel]

Thanks Chris for the detailed explanation!
All the points you raise makes sense to me - except the eddy current one. Could you explain that a bit more? If there are eddy currents in the rotor, would they not go to frame through the bearings at 50 Hz too?
Cheers,
Joe

[Keith_W]

Hi jhovel,
Have a look at this site AEGIS® Shaft Grounding Brush: Bearing Protection for Life (http://www.est-aegis.com/)
They explain the effects of shaft voltages very well on bearings, it it more evident in very large motors than the small motors that we use on our machine tools. shafts.

Regards,
Keith.

[eskimo]

my limited understanding of what some of the problems seen in standard motors operating at high frequencies >80-100Hz are:
harmonics, resonance causing premature damage and resulting failure,
electrical shaft currents damaging bearings, insulation stress, mechanical stress (motor not designed for high rpm)

and thanks Cba for your detailed information...
but & in your opinion, can a 4 pole could run at 200Hz ok?

[BobL]

.
.
.
Be careful with the motors from H&F with inbuilt speed controller. The speed range is very limited (600-1800rpm), suggesting very low torque at lower speeds. I suspect these are internally only single phase motors.
.


The motors are supposedly 3 phase motors with a built in rudimentary VFD. That's probably why they cost so much.

[cba_melbourne]

Thanks Chris for the detailed explanation!
All the points you raise makes sense to me - except the eddy current one. Could you explain that a bit more? If there are eddy currents in the rotor, would they not go to frame through the bearings at 50 Hz too?
Cheers,
Joe

Joe, yes they do at 50 Hz too, but it is too low a voltage to cause serious trouble. But VFD do not use a nice smooth sine wave. VFD's artificially reproduce the outline of a sine wave by switching the current on and off in fast succession. Modern PWM (pulse width modulated) VFD's use a chopper frequency of 12 and 16 kHz to do this. The higher this chopper frequency, the less noise you hear, but the more losses are and the more problems. Causes of problems creating high bearing currents are a mixture of fast flux changes and capacitive coupling from Stator winding to rotor. Complex stuff even for a VFD drive design engineer.

It is a huge problem for large and expensive high HP motors. But the way I see it, not too much of a problem for small HP motors. In any case, one can buy many spare bearings for a 1 or 2 HP motor with the saving from avoiding the outlay for a VFD rated motor.

I did a quick google search for "bearing current problem causes" and found more than I will ever need:

Bearing Current Problems: Causes, Symptoms, and Solutions | content content from Electrical Construction and Maintenance (EC and M) Magazine (http://ecmweb.com/content/bearing-current-problems-causes-symptoms-and-solutions)

http://www.vibescorp.ca/learn-about/shaft-currents/

Chris

[cba_melbourne]

but & in your opinion, can a 4 pole could run at 200Hz ok?

Eskimo, I have tried 3 cheap standard TEFC 4pole motors of 1/2 and 3/4 and 1 HP to see where the limits are. I used both old tech V/Hz and moder Vector drives. The 1/2HP motor had his fan removed to exlude its influence.

In all cases, I found the motors to have near constant power from 60 Hz (see note 1) to about 80Hz at higher frequencies power output drops. The motors remain usable quite well for a machine tool up to 100Hz. For light power work such as finishing cuts or polishing on a lathe, or small diameter milling on a mill, the motors remain usable up to about 120Hz. Increasing the frequency further the motor can barely overcome its own losses, and at somewhere about 140-160Hz the motor will not increase rpm with frequency anymore and become unstable and may suddenly stall depending on controller. So to answer you question, no an ordinary low cost run of the mill 4-pole motor cannot run at 200Hz.

Below 60Hz the motors have constant torque, a V/Hz drive about down to 25Hz, A sensorless Vector drive maybe down to 10Hz. The V/Hz drive will begin to run rough and erratic below some 12Hz, The Vector drive will run smoothly down to 3Hz. That is why it is generally assumed a V/Hz drive to have a 1:4 speed ratio, and a Sensorless Vector Drive to have a 1:6 speed ratio. The difference is in the low speeds, not in the high speeds.


Note 1) all small motors are designed for 60Hz, regardless what the nameplate says, so the makers can serve several markets with the same components. That is why the highest power output is at 60Hz, not at 50. A motor rated 1HP at 50Hz is capable of about 1.15Hp at 60Hz cause it is designed as a 60Hz/220V motor IF sold to North America AND be capable of running in Australia at 240V/50Hz without overheating AND still deliver the rated 1HP power if run at 230V/50Hz in Europe.

Chris

[GSRocket]

Just want to thanks you guys for a good discussion.
I'm starting to get some understanding of it