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From: msf@amelia (Michael S. Fischbein)
Newsgroups: comp.misc
Subject: Re: IBM mainframe for sale (Really 400/416 Hz power for Crays)
Message-ID: <3011@ames.arpa>
Date: Tue, 6-Oct-87 19:40:15 EDT
Article-I.D.: ames.3011
Posted: Tue Oct  6 19:40:15 1987
Date-Received: Fri, 9-Oct-87 22:45:13 EDT
References: <4673@nsc.nsc.com> <2944@phri.UUCP> <365@nuchat.UUCP> <2952@phri.UUCP>
Sender: usenet@ames.arpa
Reply-To: msf@amelia.UUCP (Michael S. Fischbein)
Organization: NASA Langley Research Center, Hampton, VA
Lines: 32

In article <2952@phri.UUCP> roy@phri.UUCP (Roy Smith) writes:
>In article <365@nuchat.UUCP> jaym@nuchat.UUCP (Jay Maynard) writes:
>> Have you considered just *how much* a Cray [...]  would weigh if they
>> used 60 Hz power instead? Not to mention the hum from the massive
>> transformer cores vibrating at 60 Hz, and the energy loss...
>
>	Still doesn't make sense.  Surely the weight you get to save in the
>cores is more than offset by the M-G set you need to turn 60 Hz into 400
 etc.

Not only aircraft, but much shipboard equipment uses 400Hz.  The goal is
certainly not saving weight.  In most case, the answer is fairly simple:

Most electronic equipment, especially digital stuff does not run on AC
at 60Hz, 400Hz or any other sine wave; it runs on DC.  Now, how do you
convert AC to DC?  (Basically)  A full wave rectifier and a capacitor to
fill in the ripple.  How big does the capacitor have to be?  Depends on the
frequency of the incoming AC.  Higher freq, smaller cap.  Look at your
computer's power supply sometime; bet more space is taken up by capacitors
than any other component (not counting heat sinks; that's not electronics
but mechanics).  Take a look at some of the big iron power supplies;
they have some truly monster caps in some machines.

So that's wye we delta the freqency (bad pun, sorry): make the conversion to
DC more efficient.  Check out switching power supplies in an electronics
text.
		mike

Michael Fischbein                 msf@prandtl.nas.nasa.gov
                                  ...!seismo!decuac!csmunix!icase!msf
These are my opinions and not necessarily official views of any
organization.