14 Jul
2021
14 Jul
'21
6:21 a.m.
On Jul 13, 2021, at 11:34 PM, Chris Zach via cctalk
<cctalk at classiccmp.org> wrote:
A number of the large disk drives use 3 phase motors; RP04/5/6 are examples as well.
Three phase motors won't run on single phase power without help from run capacitors.
(There is no such thing as "two phase power" -- 220 volts is single phase,
balanced.)
If the issue is motors, a "variable frequency converter" will do the job easily.
I have suggested in the past that three phase power supplies could run from those, but
others have pointed out I overlooked some issues. So that's probably not a good
idea.
If you need three phase power to feed power supplies or other non-motor power consumers,
the best answer is probably a "rotary converter". You can find those in machine
tool supply catalogs. Basically they are a three phase motor equipped with run capacitors
so they can be fed single phase power; the three phase power needed is then taken off the
three motor terminals. You can think of these as rotary transformers -- dynamotors in a
sense, for those of you who remember electronics that old. :-)
Don't look at "static converters" -- those are only for motors, it seems
they aren't much more than run capacitors in a box. They won't help you for
anything other than a motor, and even for motors they aren't very good.
paul
When we got an 8530 at work in the early 90s
(needed a machine with a
Nautilus bus for specific hardware testing), it was definitely a
3-phase machine and since we were in an industrial setting, I just
tapped into our panel at the back of the warehouse and wired up a
3-phase outlet for it. It never sat on our datacenter floor as a
result, but it really only ever had one purpose and that wasn't a
daily driver. Too much power, too much heat for so few employees (at
that stage of the company).
Interesting. Were the power supplies 3 phase input? Like you I have noticed that most pdp
and vax gear just pull 120 volt legs off the 3 phase to balance power loads. So you can
run them on a couple of 120 circuits. Outside of say the RP07 (which is a real 3 phase
motor)