didn't someone tell me that telco equipment had 40vdc racks once?

[Billy Crook]

DC is also great at:
Corosion
Explosions
Arc welding
Electrocution

I wonder if the cost savings take into account the price of all that
thick copper needed to transmit DC throughout the datacenter.  I've
seen firsthand, 2 inch copper cables.  There's a datacenter downtown
that already has dc infrastructure in place, and a big battery, power
stepping/switching, and UPS room.  It might be more energy efficient,
but I wouldn't bother with it, unless you could deliver +-12, =-5, and
+3.3 to the rack.  DC-to-DC conversion is notoriously inefficient.  If
you totally ruled that out, you might actually *see* some of the power
savings.  The other problem I'd see is with DC, the voltage
(noticeably) decreases over distance.  If that's noticeable in a
datacenter, you'd have to have same-length runs to each rack.  Might
be especially nice if you didn't have to cool the large AC-to-DC
substation as much as the datacenter, or if you could just put it on
the roof.  It will also probably be less safe, by the nature of DC not
pulsing to release two shorted connections.  DC circuit breakers are
more expensive, and most folks are less experienced with DC.

On Dec 19, 2007 6:56 AM, Oren Beck <orenbeck at gmail.com> wrote:
>
>
>
> On Dec 18, 2007 8:22 PM, David Nicol <davidnicol at gmail.com> wrote:
> > I've been suggesting this kind of thing for years
> >
> > http://www.news.com/8301-11128_3-9835281-54.html?part=dtx&tag=nl.e433
> >
> >
> > --
> > Looking back, I realize that my path
> > to software as a career began at the
> > age of seven, when someone taught
> > me to count in binary on my fingers.
> > _______________________________________________
> > Kclug mailing list
> > Kclug at kclug.org
> > http://kclug.org/mailman/listinfo/kclug
> >
>
>
>  Actually, the standard telecom voltage has been 48 vdc,
>  With two interesting triviata.
>
> The term "Ring" refers  to the ring of a plug that is the direct ancestor of
> what we use for musical instruments today
>
> So "Tip" refers to the TIP of that same plug.
>
> The other odd details of note are  that in the original "Bell System" most
> phone wiring for POTS was on either Red Green Yellow 3w cable or Red Green
> Yellow Black 4c wire.
>
> The oldest connections used Red and Green for the talk and dial circuit and
> the Yellow was often used for either Ringing or party line user
> identification -where the GREEN wire was POSITIVE and called TIP.
> The RED wire was Negative and called Ring
> The Yellow wire was called SLEEVE or the rearmost part of the plug  with
> BLACK as a second sleeve in my recall of the systems. Curiously when I fact
> checked myself the Yellow wire use seemed to be regional and not totally
> consistent even in the same region..
>
>
> Oren Beck
>
> 816.729.3645
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>
>