21 Jan
2009
21 Jan
'09
6:10 p.m.
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
lead.
That's the basic design, though there are better ones that are somewhat
more involved.
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.
Again, that depends on the design. I've read several long articles on
the subject in various on-line and paper publications. At least one of
them came with a lot of detailed testing including scope traces showing
waveforms and balance. Both were excellent. I don't have the article
at my fingertips; it probably was in Home Shop Machinist.
The 70% number you quote seems low. Perhaps you are thinking of "static
converters" which are not much more than a capacitor or two -- the
machine's motor is connected as you describe above. Or maybe it's
applicable to the most basic rotary converters, but not the more
carefully tuned kind with multiple capacitors.
In any case, the waveform for 3 phase power supplies isn't all that
critical. Harmonic content is no big deal, the rectifiers cause a whole
lot as they draw current only on the voltage peaks. The main concern
would be that there are no high voltage spikes, but I don't see that
being a risk with rotary converters.
paul