[Novalug] powering computers

John Franklin franklin@elfie.org
Fri Jan 22 09:51:05 EST 2016


Most servers take a standard 120v or 240v supply and convert it as you mentioned.  But there are servers that can be ordered with DC power supplies and some data centers that prefer that.

The big benefit of a DC power supply is less heat generation.  Cooling for data centers is a problem and places that offer discounts for DC powered servers do so to reduce their costs for cooling infrastructure and operation.  The downside is the DC lines suffer voltage drops over distance and even relatively short distances (such as from the basement to the third floor and across the room) can be enough to cause problems.

The solution is generally to run the main feeds on AC and put an AC to DC converter per rack or three.  For redundancy, data centers prefer (or at least used to prefer) to have servers with dual power supplies, each connected to a separate circuit, but that doubles the number of AC to DC converters needed.

jf

On Jan 22, 2016, at 9:25 AM, pereira via Novalug <novalug@firemountain.net> wrote:

> Hi List,
> 
> an earlier discussion about a computer powering on and off erratically, perhaps
> due to an old power supply (PS) or a voltage regulator (VR), mentioned that modern
> motherboards (MB) use mostly +12 V from the PS the computers; a VR circuit on the
> MB then brings this down to the right voltage, + 5 V or +3.3 V or maybe some other
> voltage for future chips. If this is indeed so, would it not be possible, and perhaps
> preferable, to run the computer of something like a car battery rather than a PS?
> 
> One of my uninterruptible power supplies (UPSs) had 2 12 V batteries in series,
> so 24 V direct current (DC). The electronics in it brings it up to 110 V alternating
> current (AC), after which the computer's PS brings it back down to 12 V DC and
> 5 V DC, which may not be actually used. Going up and down in voltage a few times
> seems really dumb.
> 
> Am I right?
> 
> Nino
> 
> 
> 
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--
John Franklin
franklin@elfie.org






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