Re: Want to move to all 208V for server racks

[Joel Jaeggli <joelja () bogus com>]

On Dec 3, 2010, at 19:25, Matthew Petach <mpetach () netflight com> wrote:

> On Fri, Dec 3, 2010 at 7:18 PM, Joel Jaeggli <joelja () bogus com> wrote:
> > On Dec 3, 2010, at 16:58, Valdis.Kletnieks () vt edu wrote:
> >
> > On Fri, 03 Dec 2010 13:21:07 PST, Matthew Petach said:
> >
> > People are still feeding their gear with AC?  Save on PS inefficiency,
> >
> > and feed direct 12/5vDC to the servers.  Save space, save power,
> >
> > save cooling.
> >
> > What does that do to customer equipment choices?  I've got a quarter acre of
> > boxes that I know want 12/5vDC inside the case, but that's not an easily
> > available option from the vendor - most of the time the only option is
> > autoswitching 120-240DC with your choice of power cables.
> >
> > The 10,000amp bus for the 12v feed for a row of server racks would be a
> > thing to behold. I don't think anyone but Paul Wall has seriously considered
> > this.
>
> Some day I'd love to meet that guy--he sure has come up with some
> revolutionary ideas here!
>
> (OK, so it's not as practical when you have other customers to worry
> about... but it might not be so crazy when you're looking at the
> efficiency numbers for 100,000 small 1u power supplies vs a set
> of much larger ones.)

Ohm's law is a bitch. 10kamp -48v DC plants are bad enough as far as the amount of copper required, running 12v for 
significant distance is comical, this is the reason small boats airplanes and diesel trucks adopt 24v systems. There's 
probably some model where top of rack rectifiers makes sense but that's really pretty much what a blade server is. When 
you look at a motherboard in a server a big chunk of of real-estate is devoted to taking 12v and switching it down to 
1.2-1.8 for distribution to the CPU/memory, a 4 socket server might have to carry 400amp around in a space of around 
300cm^2 on a layer of the pcb. 

The justification for running 208 or 480 all the way to a cabinet is all about smaller conductors.

Joel

> Matt