VAXen at home - 3ph source/MG set?

Guy Sotomayor ggs at
Fri Oct 19 21:46:04 CDT 2007

William Donzelli wrote:
>> Except that after going through a 3-phase bridge rectifier, you have
>> 360Hz (with a good DC component) vs 120Hz that drops to 0v so you need a
>> lot less filter caps with the 3-phase.  And frankly the situation I'm
>> dealing with draws ~500A @12V - that's a butt load of current over
>> single phase (and that's just the stuff that *requires*
>> 3-phase...there's a bunch more power that splits the phases to get
>> standard 120v single phase).  Total load requirements are 70A across all
>> 3-phases (210A single the *hell* are you going to wire that?).
> If it is a KL10, you will not need to worry about this at all, because
> the power supplies will fail anyway.
> But seriously...
> If you are dealing with something as big as a KL10, I think having
> real 3 phase is basically required. I would not even try it with a
> converter - god only knows how many HP the motor would need to be.
> Does your building not have 3 phase service available?
No, I have 125A 3-phase service into my's barely enough.  :-/
> If you were dealing with something like VAX-11/780 sized, with much
> lower current requirements, you probably could sling a bunch of extra
> caps on the side and have everything happy. Big ass 20 volt
> electrolytics are dime a dozen.
Na.  All of the supplies in the 11/780 are single phase (with std 110v 
15A plugs even).  The power controller just splits the phases.  As I 
said before, it simplifies the wiring from the system to the "mains".

My DS570 uses a 3-phase power controller also.  Again, it's convenient 
but not exactly necessary.


TTFN - Guy

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