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From: jgd@Dixie.Com (John G. DeArmond)
Newsgroups: sci.electronics
Subject: Re: 1 phase to 3 phase conversion
Message-ID: <8898@rsiatl.Dixie.Com>
Date: 29 Mar 91 06:04:20 GMT
References: <1991Mar28.191005.1653@rodan.acs.syr.edu>
Distribution: na
Organization: Dixie Communications Services
Lines: 51

mamiller@rodan.acs.syr.edu (Mark A. Miller) writes:

>Hello! A machinist friend of mine is buying some equipement that runs
>on 3 phase power and requested me to build a converter for him.  

>in the direction of some good references for building a converter
>(preferably non-mechanical; i.e. no motors/generators). 

You don't want to spend your friend's money trying to build a 3 phase
sine wave inverter with sufficient reserve to supply starting inrush
to the motors.  Not only would the components be expensive, the 
development would be bloody, with lots of blue smoke leaking out.
This is the voice of experience speaking.

What your friend wants to do is a) find out about a 3 phase drop
from the power company.  The way to go if the minimum is not too high
and is available.  b) get a rotary converter or c) get a motor-generator.

The rotary converter is a motor-like device with a special rotor that 
runs on 1 phase  power and outputs 3 phase power at pretty much whatever
voltage he needs.  They have slightly less efficiency and a poorer power
factor than motor-generator (M-G) sets but are a lot less expensive.

An M-G set is better than a rotary converter, having a better power
factor, a better efficiency, and with an appropriate flywheel, the ability
to supply locked rotor current requirements typical of starting motors.
ON the downside, it requires more maintenance.  Check your local motor supply 
or motor repair shop for prices for either device.

>Also, could
>someone tell me WHY it would be preferable to run a machine on
>3 phase power?  I can't really think of a good reason, but there
>MUST be one, right?  Thanks alot for any responses! (I'm a practicing
>THEORETICAL physicist, so please keep the jargon to a tolerable
>level ;-) ).

Sure.  3 phase motors don't require any external phase shifting components
such as capacitors to generate the rotating magnetic field that drives
the rotor.  Neither does a small ( up to a few hundred HP) motor require
any special starting equipment.  And since the magnetic field rotates
faster than single phase motors and for other reasons, more power per
volume and weight is possible.  Finally, the efficiency and power factor
is generally better.

John

-- 
John De Armond, WD4OQC        | "Purveyors of speed to the Trade"  (tm)
Rapid Deployment System, Inc. |  Home of the Nidgets (tm)
Marietta, Ga                  | 
{emory,uunet}!rsiatl!jgd      |"Politically InCorrect.. And damn proud of it