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From: brian@ucsd.Edu (Brian Kantor)
Newsgroups: sci.electronics
Subject: Re: wanted: device to turn brownouts into blackouts
Keywords: brownout blackout
Message-ID: <32107@ucsd.Edu>
Date: 17 Apr 91 03:52:21 GMT
References: <1991Apr15.180755.19771@odin.corp.sgi.com>
Distribution: na
Organization: The Avant-Garde of the Now, Ltd.
Lines: 32

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.  The
second time, it took out the CPU power supply, the other disk, the
console, and the fuses in the mains receptacle on the wall.

The next day, I built a device using a simple AC relay and one of those
Amperite thermal time-delay relays that look like old octal radio tubes.

With power off, the AC relay was deenergized, and applied mains power
to the Amperite heater.  After a suitable delay (I think I used 2
minutes), it would energize the AC relay, which would latch itself on
and deenergize the Amperite, which then proceeded to cool off.  If
power went off for more than a few milliseconds, or if the voltage fell
below the hold-in value for the AC relay, power to the entire computer
would be cut off cleanly, and it would not be powered back up until the
electricity had been up solidly for the two minutes.

Something like this could be used to turn a brownout into a power fail;
you can fiddle with the AC relay spring tension until you get it to drop
out at whatever voltage you think is appropriate.

Of course, there are solid-state circuits to do this as well, or better,
but the relay is something you can easily build yourself, given that you
have some experience with constructing electronic devices.  Keep in mind
that there are hazardous voltages and currents involved, and you'll be ok.
	-  Brian