Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!elroy.jpl.nasa.gov!ncar!news.miami.edu!mthvax!wb8foz
From: wb8foz@mthvax.cs.miami.edu (David Lesher)
Newsgroups: comp.dcom.modems
Subject: Re: Why do they insist on power cubes???
Message-ID: <1991Jan05.200453.28566@mthvax.cs.miami.edu>
Date: 5 Jan 91 20:04:53 GMT
References: <139957@pyramid.pyramid.com> <4299@kitty.UUCP>
Reply-To: wb8foz@mthvax.cs.miami.edu (David Lesher)
Distribution: usa
Organization: NRK Clinic for habitual NetNews Abusers
Lines: 25

In <4299@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes:


>	I have replaced power cubes with common power supplies and
>transformers, but a few words of caution are in order for reasons other
>than the above:

>1.	Many modems depend upon electrical isolation of their power cube,
>	and tying more than one modem into a common DC power supply or
>	AC transformer can result in serious impairment of the modem.

>	As an example, some AT&T modem racks use a common transformer
>	having independent *isolated* secondary windings.


Anyone got any idea why my Microcom 2400's seem to want
a center-tapped 19.6 volt xfmr, with the centertap connected to
the ground pin of the power line. To my mind, that sacrifices
the transformer isolation.

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