Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site ecsvax.UUCP
Path: utzoo!watmath!clyde!bonnie!akgua!mcnc!ecsvax!hes
From: hes@ecsvax.UUCP (Henry Schaffer)
Newsgroups: net.lan
Subject: Re: Stand-by power supply for a Broadband cable plant
Message-ID: <505@ecsvax.UUCP>
Date: Sun, 29-Sep-85 13:43:47 EDT
Article-I.D.: ecsvax.505
Posted: Sun Sep 29 13:43:47 1985
Date-Received: Tue, 1-Oct-85 03:30:49 EDT
References: <373@harvard.ARPA> <4413@amdcad.UUCP>
Distribution: net
Organization: NC State Univ.
Lines: 16

> I expect that most standby power supplies can switch fast enough to
> keep your equipment alive. We are using one ... which switches
> in about 10 mS. 
> -- 
>  Phil Ngai (408) 749-5720

  When switching the AC power to equipment, and trying to do it
fast - sometimes problems relating to phase coherency of the power
sources can arise.  In high current equipment (which your's
probably is not) you can have a very high current inrush if your
standby current is switched in out of phase with the current
which previously was there.  (It has to do with the remanant
magnetic field in the transformer.  It can get particularly 
tricky when powering large AC motors.)  This doesn't happen 
(of course) when switching between two DC sources.
--henry schaffer


Brought to you by Super Global Mega Corp .com