Re: [CAD_CAM_EDM_DRO] Rotary phase converter

Carlos Guillermo wrote:

> Hi all -
>
> 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,? 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? I've never used
> one, and I'm trying to figure out how and when they "self-start".

The rotary phase converter will just be left running all the time the
machine is in use. There will be a contactor between the rotary
and the motor loads, to start and stop the spindle. In general, other
loads can be run off the rotary, but it is best if single phase loads
be connected to the 2 hot lines of the single-phase service.

> 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.

The larger motors have lower inductance. The PWM scheme of the
VFD is designed with the motor's inductance as part of the circuit.
If the inductance is much less, then larger currents will flow, and
it may cause unnecessary trips of the over-current. Also, the starting
draw will be higher. You can place external inductors in series with
the 3 phase wires to compensate for this. If you are running the
VFD on single-phase power, you should use an even LARGER
VFD than the motor rating, ie. a 7.5 HP VFD for a 5 HP motor.

Jon