Re: [CAD_CAM_EDM_DRO] inverter question

afogassa wrote:

> Hi All,
> I've got a 200hz 220v 1Kw 4.3amps spindle motor for my router,
>and made a trip to the local electric supplyer to get a inverter to
>run it, to my suprise they sayd that I would need a 16amps inverter
>to run the spindle becouse the start current is very high.
> Well I do Know that they have a 7amps inverter for half the price
>than the one they want to sell (16amps).
> Question: would a 7 amps be enough to run this spindle or they want
>to push a bigger inverter just becouse it's more money?
> Does the 200hz have something to do with the high start current?
>making it impossibe a 7amps invert to start it?
>
>

What you really want is an output reactor (inductor) between the VFD and the
motor. The starting surge can be made almost nonexistant as the VFDs
can be programmed for whatever acceleration rate you desire. But, the
high frequency motors have very low inductance. The VFD produces
400 V square waves of varying duty cycles, and depends on the motor's
inductance to smooth out the current caused by these pulses. So, you
need to guesstimate the motor's inductance, and the inductance of a
standard 60 Hz motor, and supply the difference as a series inductor.

I used some 1.6 mHy inductors in an application with a 1200 Hz motor,
and it works pretty well. You will have to reprogram the VFD's
Volts/Hz curve.

In general, you don't want a much larger VFD than needed, because the
larger VFD's usually have a lower PWM frequency, which makes the
inductance problem much worse. Using a larger VFD to brute force
it may protect the VFD at the expense of the motor getting burned up!

Jon