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Posted by on June 16, 2008, 4:34 am
Please log in for more thread options > wrote:
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> > > On Sun, 15 Jun 2008 15:16:22 -0700 (PDT), Andrew Bishop
>
> > > >what sort of maximum frequency can I run a 3 phase 3 hp motor at
> > > >running 240 3 phase without killing motor
>
> > > >Thanks Andrew Bishop
>
> > > I have the VFD set for a max frequency of 120 Hz (so 2.4 times rated
> > > speed) on my ML-7; seems to work a treat. The motor hasn't died yet...
>
> > > Regards,
> > > Tony
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> > sounds good to me
>
> > Thanks Andrew
>
> Frequency wise I'd agree - 120hz seems fine.
> However If you're doing that to a 2 pole (3000rpm) it'll be whirring
> along at 6000rpm. Personally I'd be frightened at that.
> A 4 pole (1500rpm) motor running at 3000rpm is probably OK since it's
> the same mechanical starting point as the 2 pole one.
>
> Charles
Depends on the motor, age and construction.
I once tool a 1HP brooke Gryphon, the type that was very popular a
few years ago, and operspeeded it to see how fast it would go.
Standard 1425 rev 4 poler, up to 90 Hz it was Ok but after that it got
lumpy, and started to make a noise like a phase down, at 120 hz it was
actually slowing down and getting hot.
It's all to do with the % of iron to copper and saturation, ear of
bat, tongue of newt etc.
Modern metric frame motors don't have the problem.
As a rider to overspeeding I have converted six or seven 3/4Hp 2
polers to run at 12,000 with no problems, it took a new end shield
with double bearings and a rewind but they are now running as spindle
motors on CNC routers.
John S.
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>running 240 3 phase without killing motor
>
>Thanks Andrew Bishop