Re: [CAD_CAM_EDM_DRO] Re: DC versus 3 Phase

I was wondering about VFD's and asian motors. Several years back all of
the VFD manufacturers switched from bipolar transistors to a higher speed
switching technology (IGBT). With that switch the new drives introduced
high frequency and high voltage noise on the line. That high voltage noise
would erode the winding insulations and people found motors dropping dead
all over the place. Since that time all of the American manufacturers have
switched to what they call "Inverter Duty" windings. Baldor, Reliance,
Dayton, and all the others use higher voltage insulation in their standard
motors, so the motor failures introduced by VFD's have gone away.

I had not heard that Asian manufacturers have done the same thing. I am
interested to know how many hours you have on the mill since it was
switched to the VFD drive. I think the failures will start to occur
sometime after 50 hours but before 2000 hours. This does not apply if you
have a VFD made before 1990, but by 1995 most of the technology had
switched over.


At 09:42 AM 2/20/01 -0800, you wrote:

> We're often quick to condemn "crappy Chinese", but in my case, the
> Shoptask motors are all they're rated for.
>
>Therefore, buy at LEAST a 3/4HP VFD and motors. This motor will be
>oversized, IMHO, for the mill but about the right size for the lathe.
>
>3. I LOVE the VFD on the mill. It is so nice to set an approximate
>speed ( using the belts ), then dial it right down for use with edge
>finder, then wind it back up again to mill.
>
>4. I'm less pleased with the VFD on the lathe, although that is
>largely due to the now lower power. I CAN stall the motor with an
>agressive cut and that almost always results in a damaged insert.
>