Running 3 phase 780s on single phase power

Chuck Guzis cclist at
Wed Jan 21 11:38:56 CST 2009

On 21 Jan 2009 at 11:40, Paul Koning wrote:

> Note that you can generate 3 phase power from a 1 phase supply.  There
> are electronic devices to do this ("variable frequency converters",
> devices intended to drive motors) up to 2 kW or so.  Those can also
> produce odd frequencies, so they might be a suitable substitute for a
> CDC motor generator (for 400 Hz power).  For higher power you can get
> a "rotary phase converter" which is just a 3 phase motor with some
> trick wiring.  Those are more expensive though they are easy to build
> from a suitable size surplus motor plus some capacitors.

Those rotary phase converters are nothing more than a 3-phase motor 
with the line/mains connected across two terminals and a large 
capacitor connected between one side of the line and the third motor 

They're made to run other *motors*; the output of these things is not 
a pure or balanced genuine 3-phase current and depend as much on the 
motor load as on the motor they use.  The motors that run off this 
arrangement usually manage to run at about 70 percent of their 
nameplate rating.  I would not recommend that one attempt to power 
computer gear from one of these setups.

The electronic models are quite expensive, but give better results.

You could also use a motor-alternator setup to generate your own 3-
phase current, but I'd think that maintaining good frequency 
regulation under varying loads could be a problem.


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