Re: single to three phase conversion

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Virtualgod" <mike.marcum-at-zoomtown-dot-com> 

Could that be used to run 3-phase transformers?
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Monday, April 05, 2004 2:06 PM
Subject: Re: single to three phase conversion


 > Original poster: "john cooper" <tesla-at-tesla-coil-dot-com>
 >
 > Here's a link to the scanned Lindsay booklet pages covering rotary phase
 > converters:
 >
 > http://www.tesla-coil-dot-com/images/images/RotaryPhaseConverter1.jpg
 >
 > John
 >
 >
 > ---------- Original Message ----------------------------------
 > From: "Tesla list" <tesla-at-pupman-dot-com>
 > Date:  Sat, 03 Apr 2004 10:12:09 -0700
 >
 >  >Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net>
 >  >
 >  >
 >  > > The gadgets described are capacitor-start arrangments for the three
 >  > > phase motor, generating enough torque to get it running after which
it
 >  > > runs on a single phase with accordingly reduced power.  On inspection
 >  > > they contain a large ELECTROLYTIC starting capacitor, a resistor, and
a
 >  > > relay.  I assume the Lindsay book gives construction details.  Both
my
 >  > > lathe and my mill have three-phase motors which I run this way and
they
 >  > > are noticeably deficient in torque.  There is another technique which
is
 >  > > sometimes used, but not at all convenient.  A large three-phase motor
is
 >  > > started single phase that way and, once it's running three phase
power
 >  > > can be drawn from its three connections, only two of which are
connected
 >  > > to the single phase input line.  No magic really, the three-phase
motor
 >  > > is operating as a three-phase induction generator.  Cumbersome and
not
 >  > > very efficient, but can be used.
 >  > >
 >  >
 >  >I don't know that it's all that inefficient, compared to other ways of
 >  >making three phases from one (Motor generator, solid state inverter)..
the
 >  >rotary converter DOES depend on the load being reasonably balanced.
 >  >
 >  >The other thing is that the 3phase motor being used has to be sized
 >  >appropriately. I seem to recall a rule of thumb that the motor has to be
 >  >twice the size of the load (i.e. If you want to run a 2 HP three phase
load,
 >  >you'll need a 5HP three phase motor for the converter).. probably has to
do
 >  >with the current in the windings.
 >  >
 >  >  They also make specialized devices for this application with somewhat
 >  >different rotor design and stator windings (I don't know that the wining
for
 >  >the stator uses different gauges on the line and load windings, or,
even, 4
 >  >windings). Certainly, the rotor design can be optimized from the usual
 >  >induction motor rotor designs (which are tailored to give the desired
torque
 >  >vs speed curves, depending on the mechanical load characteristics.  A
 >  >compressor or a punch press is a very different load than a fan)
 >  >
 >  >
 >  >
 >
 >
 >
 >
 >
 >