Re: [CAD_CAM_EDM_DRO] Re: VFD's

turbulatordude wrote:

>I might agree with not using lower rated motors if it was not used in
>common practice so often.
>
>When I used to sell VFD's the 10 and 20 hp units were shipped in a
>week or two, whereas the 100 hp units took many weeks, sometimes 8
>weeks or more.
>
>We would install a unit that was capable of getting the motor up
>between 20% and 50% of speed, ideally 80%. these were for
>centrifigual loads, fan motors to be exact. The VFD would run for
>weeks or months 24/7 until the unit could be switched out with the
>full rated unit. 10hp on a 100hp motor was not uncommon.
>
>

Yes, on the larger motors, this seems to work, especially in a pinch.
But, for motors in the
1-3 Hp range, the magnetizing current seems to stay pretty high, even at
no load. Or, maybe
this is only on machine tool and compressor motors, which may have a
greater service
factor designed into them. My Bridgeport 1J with 'pancake' motor draws
3.0 amps no
load and 3.3 A at full load, according to my VFD's internal readout. It
smoked my
1/2 Hp VFD, although that was a pretty inferior unit.

Jon