[Boatanchors] 3-phase for BA transmitters?

[Robert Nickels]

On 11/18/2012 3:35 PM, Nick England wrote:
> a rotary converter (motor-generator) for 1-phase to 3-phase conversion
Hi Nick,

Actually those aren't the same thing, usually.  A true M-G would use a 
separate motor to drive a generator, but the rotary phase converters in 
popular use only us a single 3-phase motor with no load called an idler, 
on which two of the terminals are powered from the single phase line. 
The rotating flux in the motor produces a voltage on the third terminal, 
basically synthesizing the third phase.     Here's a good reference on 
phase converters including details on building a rotary converter: 
http://www.metalwebnews.com/howto/ph-conv/ph-conv.html

The main differences are in how elaborate the starting circuit is, and 
whether power factor correction caps are added to help balance the 
currents in the three phases.    Any converter needs to have proper 
circuit protection, disconnect, etc as specified by code. But if you 
want to minimize complexity you can wrap a rope around the idler motor 
pulley and start it up like a lawnmower (which would bring new meaning 
to the phrase "crank up the power").

I use VFDs on some machine tools but found models that would run from 
single phase mains.  Since a VFD is basically a big power oscillator 
that generates three outputs,  many of them will run from single phase 
input power as long as you connect to the two terminals that are 
connected to the internal power supply.  The block diagram here 
illustrates this: 
http://www.amtechdrives.com/content/KnowledgeCenter.aspx?id=3

However, VFDs generate electrical noise due to the fact that most 
inverters produce a PWM output with switch frequencies in the low kHz 
range, not a true sine wave.     A rotary converter would be the best 
option I think.

73, Bob W9RAN