Re: [CAD_CAM_EDM_DRO] Phase Converter

"Mr. sausage" wrote:

> If you just want to "start a 15 hp, 3-phase motor, sort of softly", you can
> probably use what's commonly called a "soft start". These *are* SCR
> controlled devices which essentially are large light dimmers. The firing
> circuitry is not trivial for these either, but no where nearly as
> unforgiving as inverter drives. I designed the "smart" 68HC16 based ones
> manufactured by www.eaco.com.

Right, but he has single-phase power and a 3-phase motor. In this case,
a VFD that can do BOTH the phase conversion and soft-start is a great
combination.

I can say that it works well, as I have just in the last couple of days
been playing with an 11 KW VFD on a 5 Hp motor, running the VFD on
single phase 230 V. My 230 V, 2 Hp single-phase air compressor
DEFINITELY blinks the lights when it starts. It doesn't crash computers,
or anything, but the blink is quite noticable on the fluorescents!
When I started the 5 Hp lathe motor on the VFD, there was absolutely
no flicker at all. I imagine starting a 15 Hp motor on a 100 A 230 V
service would be fairly exciting. I was experimenting with trying to start
a 17 KVA motor-generator set in a guy's basement with an L-C
phase converter. This was an idea which actually would not work,
as it needed to draw approximately infinite reactive VARs, but it
did spin up the motor. That motor, running on single phase, was
drawing over 100 A of reactive current, and we couldn't hold the
100 A breaker in. I thought it was going to blow the breaker on the
pole pig!

The VFD also solves the problem of large motors drawing HUGE
reactive current at less than full load, which your home service may
not handle well.

I think trying to run the 15 Hp motor from some kind of phase converter,
static or rotary, on a 100 A home service might cause a LOT of trouble.

Jon