Re: [CAD_CAM_EDM_DRO] Phase converter how-to

On Sun, Jan 18, 2004 at 12:34:36AM -0000, metlmunchr wrote:

> A few years ago, I talked with a retired EE who spent his career at
> Onan (generator manufacturer). He had built a lot of rotary
> converters and recommended that older motors make far superior
> converters as compared to the newer and lighter ones of the same
> size. He said to look for some big old ugly thing with cast iron
> end bells as opposed to the newer motors with fabricated steel
> housings. I think he said motors made prior to 1960. As I best
> recall, he said as motors have gotten smaller for a given
> horsepower, it has altered the current saturation levels, which
> results in the newer motors being less desirable for converter use.
> Of course, for the hobbyist, older ones are cheaper too, so that's a
> win-win.
>
> Cliff

There seems to be a consensus that lower rpm motors make for better
phase converters as well; 1750 are better than 3500. I picked up
an 870 rpm 20 hp monster that probably weighs around 350lb for $10
a few weeks ago. That one will make a dandy converter to run my
CNC stuff (as well as the other machinery).

Unless you have a very rare situation where you burn out the windings,
almost nothing goes wrong with 3 phase motors other than the bearings,
which are cheap and easy to replace. Buying an old 3 phase motor is
generally a good bet, although if you wanted to be sure you can always
check the winding resistances.

Paul
--
Paul Amaranth, GCIH | Rochester MI, USA
Aurora Group, Inc. | Security, Systems & Software
paul@... | Unix & Windows