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From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: comp.misc,sci.electronics
Subject: Re: IBM mainframe for sale (Really 400/416 Hz power for Crays)
Message-ID: <2083@kitty.UUCP>
Date: Wed, 7-Oct-87 14:45:28 EDT
Article-I.D.: kitty.2083
Posted: Wed Oct  7 14:45:28 1987
Date-Received: Sat, 10-Oct-87 10:05:28 EDT
References: <4673@nsc.nsc.com> <2944@phri.UUCP> <365@nuchat.UUCP> <2952@phri.UUCP> <3011@ames.arpa>
Organization: Recognition Research Corp., Clarence, NY
Lines: 36
Summary: More on 400 Hz power
Xref: mnetor comp.misc:1416 sci.electronics:1522

[I am trying to move this discussion to sci.electronics, where at this
point it really belongs.]

In article <3011@ames.arpa>, msf@amelia (Michael S. Fischbein) writes:
> 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.

	Space is generally not a problem on shipboard electronic equipment,
nor is weight, so 400 Hz power is used on some shipboard apparatus for neither
of these two reasons.
	The reason 400 Hz is used on some shipboard equipment is to
accommodate the needs of navigation, fire control and antenna positioning
systems which use gyros and servomechanisms.  The majority of military
gyro motors, servo motors, resolvers, synchros, control transformers (the
synchro variety), other types of magnetic angle position encoders, etc.
operates from 400 Hz power.  The reason for this is that 400 Hz results
in smaller packages, better resolution, and faster response than does a
60 Hz counterpart for a servomechanism or gyro application.  While there
are shipboard fire control and antenna positioning (as in radar) systems
which use 60 Hz for servomechanisms, today it is more common to see 400 Hz
being used.

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
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