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>From HEINKELN@firga.sun.ac.za Thu Mar 28 13:37:04 1996
From: "Leon Heinkelein" <HEINKELN@firga.sun.ac.za>
To: andre@capes1.vector.co.za (Andre Skarzynski)
Date: Thu, 28 Mar 1996 13:33:29 GMT+200
Subject: Re: Converting 3-pahse VAX Power.

Hello Andre

> > Here is a note from my friend about how he converted his VAX to 
> > run on single
> > phase. I am sending it to the list, as a few people where intereseted and I 
am 
> > sure others may be too.
> 
> And just to make sure you don't do a big mistake: *Never* do this
> with a VAX86x0.
> 
> They really *do* need the 3-phase. The large fans are 3-phase motors,
> so unless you have all three phases, your fans ain't going to run.
> And the 86x0 is made with ECL, so you can guess what will happen
> pretty fast.
> 
> For the same reason, never connect an 86x0 with the phases backwards,
> or you'll get your fans running backwards, which will lead to the
> same result (which I'm sure someone from LUDD can tell... ;-)
> 
>     Johnny
> >

Ja, ja. Just a little common sense and a bit of electronics 
background is all you need. Put in single phase fans and the mod will 
work. Exactly where/how to do it on a 86X0 (or a 88X0 for 
that matter) I have no idea , I'm not very familiar with 
those machines. Goodness knows what line current one of those ECL 
machines will draw using single phase power , I would make sure the 
cables are ADEQUATELY rated ! This of course is the REAL reason for 
using a multiple phase supply on such a machine (not just to run the 
fans and make your life difficult). It reduces considerably the line 
current , and in doing so allows cables of reasonable cross section 
to be used , obviating problems with voltage drops over long cables , 
etc. Also , the ripple at the output of the 3-phase rectifier of 
higher frequency than that obtainable with a single phase rectifier 
(you have 3 voltage (or current) cycles per 360 degrees) , so you can 
get away with smaller smoothing caps also.

Ja , ja
 and so one rambles on.
 
 Regards
 
 Leon
 

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