TELECOM Digest OnLine - Sorted: Re: Power Strips for Home Networks

Re: Power Strips for Home Networks

Dan Lanciani (
Tue, 21 Jun 2005 23:05:53 EDT

> One thing you can do is run several devices off of one power supply,
> if you have enough of them with the same voltage demands.

You have to be very careful when attempting this with devices that
have external connections to other systems. Some wall-wart-powered
gadgets rely on the isolation provided by the power supply to
implement various regulation and voltage-splitting tricks. That is,
the negative side of the power input may not be at the same level as
common of any i/o port. If you try to power two devices that disagree
about common from the same supply and they share some other common
path you will at best cause failure and possibly cause damage.

I have an IR i/o box whose power-input, IR-in/out, and RS232 commons
are all different. Of course, this kind of problem can bite you even
without sharing power supplies. I have a text-to-speech box whose
audio-out "ground" is really the bottom leg of a push-pull driver of
some sort. If I plugged this output into a grounded amplifier without
an isolation transformer the driver would be shorted through my
computer's ground connection to the box's RS232 port.

Dan Lanciani

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