Looking for VAX6000 items

Paul Koning paulkoning at comcast.net
Wed Jul 14 08:21:05 CDT 2021

> On Jul 13, 2021, at 11:34 PM, Chris Zach via cctalk <cctalk at classiccmp.org> wrote:
>> 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)

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.


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