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ask hn) PC/servers, why don't we have externalized power and battery-modules?

3 points by high_density ↗ HN
someone told me "laptop batteries are basically built-in UPS"... and I came to wonder, why don't we have a set-up like:

external-power-supply (like laptops, but bigger, that does AC --> DC)

--> external battery (stores DC, outputs DC. Also, much more easily replaceable)

--> actual server/desktop

(+ some power-negotiation / other stuff going on between 1-2-3)

without UPS-set-up's AC->DC->AC step, there'll be some few power-saves (like 10%?). And the set-up will be much more cheaper/replaceable...

why don't we have this yet? is this something impossible? Or did someone else try and failed?

6 comments

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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)
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?

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