# lets speed things up



## hudmut (Jan 2, 2010)

Ok iv got one here that i cant fine a a answer for. I have a VDF running the spindle motor on my cnc mill its a 1350rpm motor at 50Hz. 

So i have the VDF set at 125Hz to get some high RPM but i would like more in your eyes what is a safe setting for the motor nothing is even got worm yet along with the head bearings. ????


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## JimM (Jan 2, 2010)

Not sure if it's universal but the instructions for my VFD said max setting was 150% of motor frequency and that was only good for 30secs !!


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## BobWarfield (Jan 2, 2010)

If the VFD specs say it's ok, then it's a matter of bearings in the motor and spindle.

If all those bearings stay under circa 140 degrees F, and most importantly, if the temps are stable, it's probably ok. Rising temps as you leave it running can really lead to some nasty problems.

Best,

BW


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## joegib (Jan 3, 2010)

Hi hudmut,

Like you, I'm carrying out a project that involves running a 4-pole 1350rpm motor at twice (or more) its rated speed. Being similarly concerned whether this was safe, I looked at the manufacturers' spec sheets for my motor and similar types. The specs included the bearing types employed and I found that for a given motor frame size/spindle diameter, the manufacturers were using exactly the same bearings for both their 4-pole and 2-pole motors. Makes sense really  4-pole machines command a higher price anyway so it would be perverse penny-pinching to provide them with lower-rated bearings than their cheaper 2800rpm counterparts. So, the odds are your 1350rpm 4-pole motor should be fine running at 100Hz at least, though you might like to check the motor spec sheets, bearings in particular, to be on the safe side.

Taking the idea further, you might also check whether your motor is specified for both 50/60Hz operation. If it is, then its bearings must be rated for the higher running speeds provided by the North American 60Hz mains frequency. The speed of a 2-pole motor running at the American frequency is commonly stated to be around 3450rpm. On the other hand, your target is 1350rpm x 125/50Hz = 3375rpm. So, if the bearings are the same as used for the manufacturer's 2-pole machines, and the unit is specified for 60Hz operation, you should be OK for 125Hz operation as well.

The above remarks only relate to the motor's capabilities  as JimM says, you'll need to check the VFD's duty-cycle at what is probably the high end of its operating range. You should also bear in mind that the power/torque delivery of older/cheaper VFDs is often substantially reduced at the high/low fequency ends of their operating range. That may need to be factored into your feed-rate/tooth number calculations as well.

Joe


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## Majorstrain (Jan 3, 2010)

Hi Hudmut,
If you want to take a 3phase induction motor to the limit then check these guys out.
http://www.aeva.asn.au/forums/forum_posts.asp?TID=1237&PN=1

I work with the guy that goes buy the name acmotor, he has done exactly what you are looking at with a Danfoss controller and both a test motor of 0.37kW and an 11kW motor for his car. 
	

	
	
		
		

		
			




Plenty of recorded data to put your mind at rest
He did get the 11kW motor rewound to a lower voltage and balanced to a higher standard.

Hopefully not off topic.
Cheers,
Phil


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## shred (Jan 3, 2010)

It really depends on the motor. The old motor on my mill doesn't like going above 120%, but I've seen others be happy at 150%.


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## hudmut (Jan 3, 2010)

well thank you all for you diffrent ideas and things to look at.. 

Well i did some testing to day first of i fitted new bearings as they was in stock. But with the motor back on the machine and over about 1hr i got the motor up to 175Hz in 25Hz steps at a time with out any thing getting any hotter than it was before.. So then just to see i wound the VDF up to see how high it would go well 350HZ is wear it stoped i dont thing i would even dream of pushing my look at that i dont care about the motor there cheap its the spindel id have bad dreams about. (i never run the motor at 350Hz before you all call me mad)


So im going to try and run it at 150Hz for a few jobs and see what goes in to melt down first. As most of may machine runs are under a hr im sure it will be fine for a few parts to see what it will stand up to.


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