
ask hn) PC/servers, why don't we have externalized power and battery-modules? - high_density
someone told me &quot;laptop batteries are basically built-in UPS&quot;... and I came to wonder, why don&#x27;t we have a set-up like:<p>external-power-supply (like laptops, but bigger, that does AC --&gt; DC)<p>--&gt; external battery (stores DC, outputs DC. Also, much more easily replaceable)<p>--&gt; actual server&#x2F;desktop<p>(+ some power-negotiation &#x2F; other stuff going on between 1-2-3)<p>without UPS-set-up&#x27;s AC-&gt;DC-&gt;AC step, there&#x27;ll be some few power-saves (like 10%?).
And the set-up will be much more cheaper&#x2F;replaceable...<p>why don&#x27;t we have this yet? is this something impossible? Or did someone else try and failed?
======
davismwfl
For servers, a number of data centers I have been in do use DC power within
each rack or group of racks. It removes the double conversion, and AC
basically is a battery charger (this is over simplified). It simplifies the
entire system removing a number of components that would otherwise be in
traditional UPS systems.

IIRC, Google does this for their racks and I know they have published a number
of papers on it.

For home PC's it doesn't make sense given what consumers are used to with AC
power. So the current methodology makes sense, but server farms is quite
different.

~~~
high_density
oh... so I guess this isn't some doomed idea...

but I was hoping for someone else to actually make this consumer-grade so I
can use it on my company / my home :(

btw, can you give me links to the paper?

------
speedgoose
I would guess it's because it's expensive to have a lot of DC power on long
distances.

On a smaller scale, I remember the fist generation of the online.net dedibox
to have one power supply for two servers. I don't know whether it was a good
idea, I think they haven't done it since.

~~~
high_density
yes but that distance is about few kilometers... I don't think distances like
3meters will matter a lot (if we can get cables thick though)

------
brudgers
For desktops screen size comes into play. My modest 24” monitor has more than
twice the area of my generous 15” laptop display. Bigger displays are a major
reason for choosing a desktop and screens are power hungry and always on
during normal desktop use.

~~~
high_density
but most UPS is about keeping the desktop/server/router on, not the display

