Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uwm.edu!ogicse!milton!whit
From: whit@milton.u.washington.edu (John Whitmore)
Newsgroups: sci.electronics
Subject: Re: wanted: device to turn brownouts into blackouts
Keywords: brownout blackout
Message-ID: <1991Apr17.231417.5727@milton.u.washington.edu>
Date: 17 Apr 91 23:14:17 GMT
References: <1991Apr15.180755.19771@odin.corp.sgi.com> <32107@ucsd.Edu>
Distribution: na
Organization: University of Washington, Seattle
Lines: 27

In article <32107@ucsd.Edu> brian@ucsd.Edu (Brian Kantor) writes:
>In 1977, I was in England installing a computer system for my (then)
>company, and the electricity workers went on strike.  To differentiate
>the power cuts caused by industrial action from the other kinds that
>were occuring pretty regularly in that part of the country, they would
>switch the power off and on a few times over a span of perhaps 30
>seconds or so, then leave it off for several hours.
>
>The first time they did that, we lost the tape drive and one disk.

	There is a simple trick used on many machine tools (where
a power cycle could result in an unattended machine starting up),
which is to use an AC relay driven by two switches in parallel.
One switch is a pushbutton (normally OPEN), and is labeled 'START'.
The other switch is a pair of contacts on the relay, so that the
relay latches ON after the 'START' button is pressed.  A 'STOP'
button is a normally CLOSED pushbutton  in series with the
relay contacts that keep the relay ON.
	A motor-start relay usually has spring tension adjustment that could
be used to make it drop out at low AC voltage (and one could CERTAINLY
put in an IC power-fail sensor in place of the STOP button).  
	So, a simple power-drop switch could be a simple relay, START
button, and a sensitivity adjustment.  The complete systems are common
in industrial applications, so you might be able to find the whole
box in a scrap pile, ready to hook up.

	John Whitmore