Looking for VAX6000 items

Guy Sotomayor ggs at shiresoft.com
Wed Jul 14 11:33:56 CDT 2021

On 7/14/21 6:21 AM, Paul Koning via cctalk wrote:
>> 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.
> 	paul

I've found 2 issues w.r.t. "rotary converters".

  * They *always* consume lots of power regardless of the actual load
  * They typically don't have great frequency regulation as they are
    really designed for machine tools (which are pretty tolerant) so if
    the load varies, the frequency will vary until the "mass" catches up

I did a fair amount of investigation of this in order to power the 
peripherals for my IBM 4331.  The peripherals in total require on the 
order of 21KVA of 3-phase power and with them (printer, card 
reader/punch and tape drives) the load will vary *a lot) which would 
screw up the DASD (string of 3340 drives and some 3350 clones).

I ended up looking at a solid state phase converter (takes in 220v 
single phase and produces 208v 3-phase).  It has a good (< 1% frequency 
regulation) and only consumed 100W at idle.  Plus it's relatively small 
and quiet.  The downside is cost (~$5000).

TTFN - Guy

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