28 Apr
2014
28 Apr
'14
7:13 a.m.
On Apr 26, 2014, at 9:39 PM, Mark J. Blair <nf6x at nf6x.net> wrote:
On Apr 26, 2014, at 06:58 , Paul Koning <paulkoning at comcast.net> wrote:
If you really have that kind of device, it?s probably meant to be hooked up to 3 phase Y,
and all you?d have to do is hook each ?phase? to some single phase branch circuit. If
it?s delta wired, that may be more problematic since there is no ?neutral?.
If it?s a disk drive that wants 3 phase power, like an RP04, presumably it has a 3 phase
motor and any sort of motor drive power source will make it happy.
If it?s a power supply fed by 3 phase power, such as you would find in a CDC mainframe,
you probably do need actual 3 phase power or the ripple may be too high. But if so, it?s
not going to be all that picky about waveform.
Finally, I think the waveform of a rotary converter is pretty good. It?s basically a
rotary converter. ?Static converters? are a different story, those are only barely good
enough to spin a 3 phase motor on a good day. But I remember reading articles about 3
phase rotary converter construction and they sounded pretty good.
If you need only 2 kW per circuit, solid state converters might be best. I?m not sure
what the waveform on those looks like, though; those too are meant for driving motors and
they use IGBT converters, probably pulse width modulation, for that. An advantage of the
solid state converters is that they can produce a different frequency than what the power
company gives you, within limits. For example, 400 Hz 3 phase needed for CDC 6000 series
machines can be obtained that way.
paul
How much power do you need? For a modest price
you can get solid state 1phase to 3phase converters ? variable frequency motor drives ?
good for up to 3 HP, i.e., about 2 kW. If you need more than that, you can get rotary
converters that go much higher. So you don?t need to modify the machine, just add stuff
to your electric setup to make the 3phase.
I use a rotary phase converter for my milling machine and lathe. I haven't scoped out
the waveforms myself, but I got the impression from the guy who I got the machines from
(who's in the machine shop business) that rotary phase converters don't make
especially clean power. Two of the three legs are simply connected to the single-phase AC
supply, and the converter generates the waveform for the third leg. I gather that both the
amplitude and phase of the third leg vary widely from the nominal preferred values,
especially as the load impedance changes. It's good enough to make a 3-phase motor
spin the right direction, but maybe not so great for a single-phase electronic load
powered from that leg.
So, for a computer that normally takes 3-phase power but actually just has single-phase
loads internally (i.e., it's made to take 3-phase power since that's what's
available in industrial/commercial buildings, but nothing in the machine actually requires
3-phase power), I think that a single-phase conversion might be preferable to using a
rotary phase converter.