Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site sdcsvax.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!ihnp4!houxm!whuxl!whuxlm!akgua!sdcsvax!jc
From: jc@sdcsvax.UUCP (John Cornelius)
Newsgroups: net.micro
Subject: Re: Voltage protection for micros
Message-ID: <725@sdcsvax.UUCP>
Date: Fri, 8-Mar-85 11:17:18 EST
Article-I.D.: sdcsvax.725
Posted: Fri Mar  8 11:17:18 1985
Date-Received: Sun, 10-Mar-85 07:34:20 EST
References: <8296@brl-tgr.UUCP> <6200044@hp-pcd.UUCP>
Reply-To: jc@sdcsvax.UUCP (John Cornelius)
Organization: EECS Dept. U.C. San Diego
Lines: 36
Keywords: housepower voltage protection
Summary: An inexpensive solution


Well over 90% of the voltage abnormalities that will ruin your day (and your
computer) are either over/under voltages of magnitude +- 50% or
spikes/dropouts/noise lasting less than 20 milliseconds. IBM did a study about
7 years ago and concluded that the ability to ride through 2 cycles of peculiar
power without the peculiarity reaching the machine would take care of about 90%
of the power related maintenance calls.

The general form of such protection is with isolation/regulation transformers.
These fall into 3 types:

	Transformers that do one or the other

	Multitap isolation transformers that switch secondaries with SCRs

	Ferroresonant continuously regulating isolation transformers.

My prejudices lie with the last of these because they are superior to switched
designs in extreme cases of voltage abnormalities and those are the ones that
make maintenance companies rich. The maintenance company that we use buys
Isoreg transformers from us and installs them on micros that they are
maintaining under contract. When the contract goes away, so does the Isoreg
transformer. When the customer objects he sells it to the customer at 130% of
his cost. He claims that these things get rid of virtually all of the
undiagnosed intermittent problems.

The Isoreg product goes for about $.50 per watt for 750VA and above and a
little more for smaller units. They tend to run warm and the larger ones have
fans for cooling. They are heavy and not particularly pretty but if you have
irreplaceable data on your disk they are worth their weight in gold.

Isoreg is in Littleton Massachusetts. Their phone number is (617)486-9483.

John Cornelius
Western Scientific