Sunday, July 20, 2008

UPS/SMPS - idea for better efficiency.

I was thinking about computer power consumption and was annoyed that with power from a typical UPS battery, even with the monitor turned off and the CPU idle, you could still last only for 20min or so!!

Bad isn't it?

I could not get a quick fix for drastically reducing idle state power consumption of our fairly monsterous x86s (unless we used a clockless processor or at least one of those beautiful RISC machines.)

But I did think about the UPS - the fairly low battery voltage is converted to 240V with some inefficiency and back to 5V, 12V by the SMPS with some other inefficiency, which is multiplied by the first inefficiency (to get the total inefficiency) ... whoa!

If the UPS and SMPS were integrated somehow, the only user of the 240V AC power would be the monitor (well, maybe we could get an LCD monitor to work out of 12V or something? But a CRT can be tough to get to work from low voltages, especially DC voltages, because it needs really high voltages (kV) for the CRTube you know. Anyway they seem to be getting phased out on most desktops now.)

So a 12V battery, with some simpler ciruitry that can both boost and buck this (since battery voltages usually drop as they discharge). Providing 5V, 12V more efficiently. 240V AC only for CRT. Even an LCD monitor should be designed to work with low voltage supplies.
Why, even the speakers / external amplifiers use such low voltages anyway (through their own little transformer).

You save on some transformer/other electronic component costs. You get the computer to run longer during a power failure.

Edit: I just remembered google uses a simplified SMPS (12V output only), getting themselves 85% efficient ones instead of the usual multiple-voltage-output 55% to 65% efficient ones. Their whitepaper (pdf) .
It's also been discussed at Slashdot. Someone even mentioned the UPS /SMPS inefficiency thing there.


  1. Yeah. This thing you describe is called a laptop. Oh... and they also make the processor a little less power-hungry.

  2. :D Oh darn yes it is.

    I guess this is what happens when you are stuck with a CRT desktop with no physical access to a laptop for half a decade (not kidding)

    :O :D