Re: [CAD_CAM_EDM_DRO] Rotary phase converter

On Tue, 29 Jan 2002 01:01:20 -0500, "Carlos Guillermo"
<carlos@...> wrote:

>Are rotary phase converters compatible with equipment that also
>runs other systems (such as coolant pumps, brakes, CNC controls,
>etc) off of the 3 legs,?

Yes.

>Would the phase converter be trying to
>start and stop every time the spindle motor was powered on and
>off, and in doing so affect the other systems?

No, the rotary converter is started up and left running. The mill or
other equipment connects to it like it would connect to a wall plug (so
to speak). If the converter is sized properly the spindle starting and
stopping should not cause voltage fluctuations that would bother the
rest of the equipment.

One note of caution - if you have control relays, magnetic contactors,
be sure to connect the converter to the machine so that the power that
is used for control, that is to operate the contactors, comes from the
two wires incoming single phase wires.

>I've never used
>one, and I'm trying to figure out how and when they "self-start".
>Can someone please explain? Also, can I run a 5hp motor at 3hp
>with a 3hp VFD? The Hitachi literature warns against running a
>motor rated higher than the VFD's rated HP, but I can't understand
>why.

I would not recommend running a 5hp motor on a 3hp VFD. Hitachi builds
them, and they know their product, and its limitations. The VFD market
is very very competitive, cut throat in fact. If they had any hope that
their 3hp VFD would actually run a 5hp motor with out causing them to
lose money on warranty claims or create upset customers, they would sell
it as a 5hp VFD!

You can feed a 5hp 3 phase input VFD from a rotary converter with a
balanced rotary converter based on a 7.5hp idler motor and it should
work just fine. You can buy 5hp single phase input VFDs but they are
more expensive than the three phase input ones at that HP. You might
get away with feeding it from a 5hp idler if the acceleration ramps were
programmed for it in the VFD, but it isn't a good idea.

Fitch