Mailinglist Archive: opensuse (1777 mails)

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Re: [opensuse] Moving to IPv6
  • From: "Carlos E. R." <robin.listas@xxxxxxxxx>
  • Date: Tue, 14 Sep 2010 21:48:03 +0200
  • Message-id: <4C8FD173.3080609@xxxxxxxxx>
On 2010-09-14 15:11, Anton Aylward wrote:

There's _almost_ a AC vs DC issue. While Tesla may have been right in
the context that existed back then, "that was then, this is now". We
make a lot of use of DC - all our electronics runs on it, mostly low
voltage. I also have a lot of low voltage (and high efficiency) DC
lighting in my house.

Ha! But now there are also high voltage DC transmission lines. :-p

Why? For instance, to transmit power with an underwater cable to an island. In
this case, the losses
of AC transmission are higher than those for DC, as the field is formed on
water instead of air.

It might come that power transmission lines in cities may have to "go back" to
DC. It is a static
electro-magnetic field, less "dangerous" for those that oppose, saying cancer
or whatever.
Economically, it has fewer losses for underground cables, which may become the
norm in cities.

Just imagine the huge DC to DC step down or step up converters.


What is more ironic is that in the net room there is this huge UPS that
takes AC power (220V actually) and converts it to 12V. It uses that 12V
to charge batteries. The batteries then power an alternator that
converts it back up to 110V which goes to the racks. Where the units I
just mentioned convert it back down to 12V and 5V.

I can't say this makes a lot of sense to me. Surely taking that 12V
from the batteries to the racks (with some regulators etc) would make
things more efficient? Its not as the usual benefits of AC apply here,
its not as if this power is being transmitted over great distances.

Telephone exchanges run at 48 volts. Only computers and such use AC, often
taken via a converter
from the 48 volts line (with huge batteries).

--
Cheers / Saludos,

Carlos E. R.
(from 11.2 x86_64 "Emerald" GM (Elessar))

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