Re: Inverter Drives

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Tim Goldstein" <timg@k...>
>wrote:
> Unless your motor is rated for double the speed that it gets at
>60 .hz I
> would not even suggest going to 120 hz. So, I seriously doubt you
>need a
> drive that will let you go above that. An exploding armature is not
>a
> pretty sight.
>
> Tim

Further to Tims reply. I wouldn't worry too much about exploding
armatures if your motor is a 4 pole 1700 rpm one as these share the
same armature as the 2 pole 3,400 rpm ones and are obviously good for
these revs.
If however your motor is a 2 pole motor then double speeding this up
to 120 Hz could be dangerous.

What is a limiting factor though isn't the speed but the motor
design. Many motors at around the 100 Hz level get magnetic
saturation of the stator which actually causes the motor to slow and
get hot.

I have had some small rotor models rewound to accept 200Hz for
special router operations. This is a viable job provided you can get
a motor rewind company who has the nessesary expertise to work the
correct figures out. This will allow a 2 pole motor to reach 11,200
rpm on our 50 cycle mains.
Before the purists say it can't be done I have done about 7 or 8 of
these now and they are still running fine after about 6 years.
Bear in mind that our metric framed motors are only three coil, 6
wire and so are very much smaller than equivalant US motors.

To give an idea http://tinyurl.com/bie8
shows a standard 1.5 Hp Bridgy motor against an Italian 3hp motor.

John S.

> [Denver, CO]
> Sherline products at Deep Discount
> Mach1 & DeskCNC with credit card ordering
> www.KTMarketing.com/Sherline
> Now selling Visual Mill 4.0
>
>
> > -----Original Message-----
> >
> >
> > I'm looking at purchasing an Inverter drive for my milling
> > machine. The machine has a 3phase 3hp motor with a variable
> > speed head. The spindle speeds range from 80-4200 rpm.
> >
> > I'm currently looking at two Teco drives - the FM50 and
> > FM100. The basic difference seems to be that the FM50 only
> > goes up to 120hz, whereas the FM100 goes to 400hz. Will I
> > ever need/want to run the motor at >120hz? Also, ultimately I
> > want to control the rpm with Mach1/2 or EMC. Are there any
> > potential problems with either drive for doing this? Has
> > anyone else used either of these particular drives?
> >
> > Thanks,
> >
> > --C.S.
> >
> >
> > Addresses:
> > FAQ: http://www.ktmarketing.com/faq.html