[Gllug] OT: Merging UPS outputs

[Alain Williams]

On Mon, Aug 22, 2005 at 08:07:06AM +0100, John Winters wrote:
> On Mon, 2005-08-22 at 01:06 +0100, Nix wrote:
> > On Thu, 18 Aug 2005, Alain Williams whispered secretively:
> > > You could take power at (say) 5 volts -- feed is straight into your
> > > motherboard. The trouble is that everything else would need to
> > > take input at 5 volts. To get the same amount of power (volts X amps)
> > > you would need 50 times the current: which would mean having to have
> > > much thicker cables and a much greater distribution loss (ie loss
> > > in getting from the local substation to you).
> > 
> > Plus, it would be much more dangerous. What's that saying: `it's amps
> > that kill'?
> 
> Possibly more dangerous, but not for that reason.  If your power was
> supplied at just 5V, it doesn't matter how many amps are flowing through
> the cables, they won't flow through you because there isn't the pressure
> there to make them take that route.
> 
> The way it would be more dangerous is because the fuses would have to be
> much larger (to accommodate the larger currents) and thus less able to
> cut off the current before spectacular fire-inducing things happened.
> Try dropping a spanner across the terminals of a car battery to see the
> sort of thing I mean.

There would be other effects:

* Higher current -> greater heating/energy_loss in the cables; to counter
  this cable cross section would need to be 50 times as great.

* Higher current -> switches & plugs would need to be bigger (uglier ?) to cope.

* Higher current -> greater electromagnetic fields generated.

-- 
Alain Williams
Parliament Hill Computers Ltd.
Linux Consultant - Mail systems, Web sites, Networking, Programmer, IT Lecturer.
+44 (0) 787 668 0256  http://www.phcomp.co.uk/

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