Thread: CMG Motors

Originally Posted by 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.

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

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

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

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

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

> 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

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

not in any order of preference

Originally Posted by cba_melbourne

> 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.

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

Originally Posted by eskimo

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

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

Hi jhovel,
Have a look at this site AEGIS® Shaft Grounding Brush: Bearing Protection for Life
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.

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?

Originally Posted by cba_melbourne

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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.