>
> Andreas,
>
>
> The power distribution of a VAX 11/780 is much simpler than that. There
> is only one three-phase transformer in the entire machine, and it is
> used to power the shutdown interlocks.
>
> The three phases are not combined into any "wye" or "delta" arrangement
> using a transformer (other than the interlock). The front side of the
> power distribution panel consists of a bunch of standard 120V
> three-prong household outlets, and various portions of the VAX are
> connected to these outlets.
This sounds similar to the VAX 6k power supply. There are three circuits
tapped off of the three-phase power to feed various pieces-parts, and the
configuration of the DC power supply is such that two legs at 240V is a
close match to three legs at 208V
>
> It's very easy to convert an 11/780 to run from single-phase power, the
> problem is the high current draw, which is more than the typical 15A
> feed in our houses. I've been running mine for short periods of time,
> which each phase plugged into a different branch circuit in my house.
> This really makes GFI protected circuits go bonkers (for obvious
> reasons), but I've been very careful not to exceed ampacity of any of
> the branches.
A moderm dryer (30A) or range (50A) actually has all the connections
required: 2 lines, one neutral, and one ground. If the power supply
neutral is replaced with a properly-sized conductor, it shouldn't be any
big deal to change the cord and run it off of a standard dryer/range
recpt. Make sure you have both the neutral and equipment ground
avaliable-- the older style of electric dryer recpt didn't provide a
neutral, and the ground was often used to provide 120v to the timer!
>
> I wouldn't recommend this to everyone, though. I brought home a Fluke
> 41 Power Harmonics Analyzer and made a simple test harness so I can
> actually measure what is going on with my modification to the 11/780.
> When Gunther was visiting, we ran it for about twenty minutes, and
> that was the longest run of the machine in my house to date. I was
> also very cautious to make sure that none of the "phases" were causing
> any excessive heating in the wires, however, this is not a good safety
> test of the modification.
The longest run on my VAX 6320 & TU81+ was 24+ hours, on 240V 20A single
phase and 120V 30A respectively, with no adverse reactions except to the
electric meter. I feel confident enough that when I start it up For Real,
it'll run unattended 24/7 until such time as I can't afford to pay the
electric bill.
>
> After safety checks using the 41, my next step is to install those
> small inline "Power Planners" to the cooling fans. That should cut the
> power requirements of the 780 by a few hundred watts. I've tested
> those Power Planners, and for typical AC motors that do not run under
> a heavy load, they really do work and cut electrical consumption. They
> do generate harmonics, but not any worse than your typical PC
> switching power supply.
details?
>
> My eventual goal is to run the 780 from a 240V source.
>
> Any yes, my wife thinks it nuts.
^_^ My wife didn't quie realize just how big a 6K machine was...
>
>
>
> - Matt
Bob
>
>
>
>
> At 01:11 PM 2/1/2002 +0100, you wrote:
>>Gunther,
>>
>>be careful with the return line: if you are running three different
>>phases, these are phase-shifted 120 degree against each other, so the
>>current maximum on each phase will occur at a different time, and the
>>center ("ground") line will not need to carry any current at all (in a
>>perfectly balanced circuit). If balance is not perfect, the ground wire
>>will have to bear at most the same load as any of the live wires.
>>
>>If you feed a single phase into the same circuit on all three lines,
>>you will have peak current on all three "live" lines at the same time,
>>and the "ground" line will need to handle that. If it's not made to
>>that spec, you'll overload it by a factor of 3...
>>
>>I don't think this is true for VAX power supplies, but I have heard
>>about process automation computers that are fed with three phases just
>>to make the period shorter and to use smaller capacitors. With this
>>kind of power supply, you'd get a lot of ripple on the DC output.
>>
>>Regards,
>>Andreas
>>
>>Gunther Schadow wrote:
>> >
>> > Hi,
>> >
>> > just to be sure, I would simply put all three phases on the
>> > same single phase. Are there any problems with that? The
>> > VAX 6000 is much pickier, but the VAX 11 and everything
>> > having the simple power distribution box should be fine,
>> > right?
>> >
>> > thanks,
>> > -Gunther
>> >
>> > --
>> > Gunther Schadow, M.D., Ph.D.
>> > gschadow_at_regenstrief.org Medical Information Scientist
>> > Regenstrief Institute for Health Care Adjunct Assistant Professor
>> > Indiana University School of Medicine tel:1(317)630-7960
>> > http://aurora.regenstrief.org
>>
>>--
>>Andreas Freiherr
>>Vishay Semiconductor GmbH, Heilbronn, Germany
>>http://www.vishay.com
>
>
>
> Matthew Sell
> Programmer
> On Time Support, Inc.
> www.ontimesupport.com
> (281) 296-6066
>
> Join the Metrology Software discussion group METLIST!
> http://www.ontimesupport.com/cgi-bin/mojo/mojo.cgi
>
>
> "One World, One Web, One Program" - Microsoft Promotional Ad
> "Ein Volk, Ein Reich, Ein Fuhrer" - Adolf Hitler
>
> Many thanks for this tagline to a fellow RGVAC'er...
Received on Fri Feb 01 2002 - 11:21:36 GMT