[rescue] adding power redundancy to single power supply systems ?

[Patrick Finnegan]

On Mon, Mar 24, 2008 at 06:48:17PM -0500, Lionel Peterson wrote:
> >From: Patrick Finnegan <pat at computer-refuge.org>
> >I'm sure you could build one using just a single relay (with a 120V
> >coil) and the cut off ends from some power cords for about $10, maybe
> >$20 if you want a nice enclosure to put it in. :)
> 
> How do you keep the equipment from failing when it switches from one 
> output to the other?

Switch really quickly. :)

> It would be quick, but would it be quick enough? If you put a UPS 
> between the switch and the system it would work great...

It does depend on what you're powering, but there's no reason that you
shouldn't be able to get a solid-state relay (aka a few triacs plus
a little control power) to switch over in a couple cycles or less.

If that's not fast enough, either you need to disable the ACLO signal,
(you're not trying to do this to a VAX or -11, right? ;) or buy a 
bigger PSU (or better quality). :)

Pat
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