Re: [CAD_CAM_EDM_DRO] Re: Phase converter questions

Peter Renolds wrote:

>Keep in mind most VFD's will generally only work on single phase power
>up to about a 3 HP motor size. After that, they require 3 phase power
>on the input side.
>

Yes, this is the way the manufacturers rate them. However, it turns out
that
practically ALL VFDs made after 1990 will run off of single phase. If you
intend to use them heavily, it is a good idea to "derate" them, in other
words,
use a VFD with a higher rating than the motor, by perhaps 50%.

I have a 1 Hp "3-phase input only" VFD on my 1 Hp Bridgeport mill that
I have been using in a home shop environment for a number of years,
with no trouble whatsoever. When I use my high speed spindle that
draws a lot of current, I put a fan on the heat sink of the VFD to give it
a break.

> So unless you're running a 3HP or smaller motor you
>may still need a rotary converter to generate the 3 phases you need to
>supply a larger powered VFD - if you want the flexibility a VFD offers
>for motor control. I wouldn't expect many HSM's to require much more
>than a 3HP spindle motor - but I may be mistaken...
>
>

Really, the rotary converter for the VFD is pretty silly. The only benefit
of this is it gives the rectifiers and filter capacitors a slightly
reduced load.
For the home shop environement, they are already pretty adequate.
Remember, these devices are designed to run at 100% load for 5 years
continuously in a cabinet or machine room at 50 C. That heat and 40,000
operating hours far exceeds what it is likely to see in a home shop in
decades of use.

I do agree that a modest derating for the single-phase supply is a good
thing
to do.

Jon