Re: [CAD_CAM_EDM_DRO] Phase converter circuit

> While we are talking about it, I would suggest building a rotary converter -
> if you find the parts used, it can be really cheap. I made one out of a 15hp
> motor from an old elevator. The whole thing probably cost me $150, including
> the 3-phase 220-to-440 transformer that is mounted on the side of it to run
> VFD's. With the rotary converter, I get full output from the drives.
>
> It works great... except...
>
> Every time I turn it on, the high-pressure sodium and mercury vapor lights
> in my shop go out, then come on a few minutes later. Does anybody know how
> to reduce the starting current on one of these things?

Sure, put it on a VFD programmed to slowly ramp up to speed.

What you have done here is used an idler motor as a 'rotary capacitor'
to supplement the capacitors in the VFD. If you got VFD's with bigger
capacitors and diodes rated for it, you could simply run them off
single phase. The capacitors have to supply current between peaks of
the AC cycle - with single phase these occur 120 (100) times a second,
but with three phase it's 360(300) times a second, so the caps can be
smaller.

I had a rotary converter when my 3 phase machines were at home, and I
hated it. Always have to decide if I was going to use a machine again
soon, or if it was time to shut it down. I'd much rather have
electrolytic caps in a VFD.

Chris