Re: VFD for a 15HP CNC lathe

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "fuddham" <fuddham@a...>
wrote:

> I have a CNC lathe that has a 15 HP spindle motor. What size VFD
> would I need if I only fed the VFD single phase power? Would it be
> better to get a 15 hp VFD and use a rotary phase converter to feed
> the VFD? What size VFD and Rotary converter?
>
> Thanks,
>
> Scott Hamilton

15HP! Now THAT's a CNC lathe!!

Scott, 15HP VFD's get pretty pricey. Most of the solid state ones
are rated for 1 to 5 HP. On a lot of the older VFD models the HP
rating is with 3 phase in, and they have to be derated 50% for single
phase in. That motor probably draws 35A @ 230VAC and 10 times that
amount on startup for a few seconds.

A rotary converter would make more sense in this case. You need one
rated for at least the 15HP. One of the nice things about rotary
converters is that every 3 phase motor you put on the "grid" actually
helps stabalize it and becomes part of the generator. You have to
have enough 3 phase to start the first motor. If it is not loaded
then it becomes a secondary generator and you can start a bigger
motor (etc, etc). There are plans on Metal Web News on how to build
your own 3 phase rotary converter. Used Large 3 phase motors are
usually pretty cheap and you can find the caps involved surplus on
the web. Don't waste your money on the static converters.

Tom C.