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

Patrick Finnegan pat at computer-refuge.org
Mon Mar 24 21:45:16 CDT 2008

On Mon, Mar 24, 2008 at 08:35:24PM -0400, Steve Sandau wrote:
> ><snip>
> >
> >>Since it's APC I assume there is something in there that covers it
> >>during the switch. I don't know what happens if you have power
> >>coming in at different phases... I assume it sends the glitch thru.
> >>
> >
> >Dunno about phases (talking above my pay grade ;^), but it seems to
> >me that ideally the APC-type unit would essentially be a relay
> >feeding into a tiny UPS (a big capacitor?) to provide adequate power
> >for the split-second the relay is switching over.
> >
> My old boss was telling me about the switch to bring his generator on- 
> and offline. He called it something like a "make-before-break" switch. I 
> guess the idea was that the new connection was made before the original 
> connection was broken, ensuring a constant supply of electricity to the 
> load. I'm not sure how that would work since it would connect the two 
> power sources, but that is what he described.

That's different because it's a generator, where you can actually sync
it up to the power input.  Trying to do something like that on two
separate utility lines (or anything that's not designed for it) it a Bad

Purdue University ITAP/RCAC       --- http://www.rcac.purdue.edu/
The Computer Refuge               --- http://computer-refuge.org

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