Looking for VAX6000 items

Jon Elson elson at pico-systems.com
Wed Jul 14 14:12:33 CDT 2021

On 7/14/21 11:33 AM, Guy Sotomayor via cctalk wrote:
> 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
Frequency regulation comes from the single-phase mains, and 
thus will be the same as the utility provides.
> 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).

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