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I always thought that using a conventional UPS with a PC is highly inefficient. Power goes from AC -> DC -> AC in UPS and then AC -> DC in PC SMPS. Since PC works only with DC (12, 5 and 3 volts) It should be possible to convert AC -> DC once and use that to charge SLA battery and drive a PC.

Sure enough there are solutions for this. For example PicoUPS-100. These are designed for embedded PC, but I see no reason why such a device cannot be used for home PC also. Place where I live has frequent power outage and if I can hookup couple of battery with such a system it would give me long battery backup time with minimal cost if I use a power efficient PC.

Does any one have any experience with such systems for a mainstream (home) PC.

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This makes me think it's only a matter of time until power supplies have their own UPS built in. –  Scott Jul 15 '09 at 18:18
    
I've thought about this for some time, you should look into Zenner Diodes, 12V car batteries and home made battery chargers ;) –  voyager Aug 4 '09 at 1:33
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@voyager: the Zener diode in those battery chargers is used as a voltage reference. The constant voltage is then used with a potentiometer for manual adjustment of the set value for the battery voltage. –  Peter Mortensen Aug 4 '09 at 10:44
    
Google implements something very close to this for the trip delay between main supply going down and their UPS coming back up. Gigabyte makes custom boards for this, see if you can grab one at the regular Google sales. –  PoorLuzer Oct 25 '10 at 0:21

4 Answers 4

Google does exactly that! They do not have the UPS in the datacenter, they have the UPS on the machine itself, and feed DC to the mainboard. And they are only feeding 12V, as it is more energy efficient than lower voltages.

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Yes! I am aware of it. Google server actually convinced me that this is viable, but here I am looking for some info about the same technology for home users. –  Rajkumar S Jul 15 '09 at 15:10

Make sure you take a look at Mini-box.com's selection of DC-DC ATX PSUs.

EDIT: I see that your original link is from there! :-) I will actually be buying one of these this summer, as I notice that their selection has increased to include some ranged input voltage PSUs. Look at the M4 enclosure for mounting in a more traditional style. Then, you can run wires direct to your box. Visit your local hardware store for some good insulated options. Or, hack a cable to a power supply that you don't use any more, etc.

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I've thought about this for some time, you should look into Zener Diodes, 12V car batteries (SLA) and home made battery chargers. Cheap and interesting.

I've seen mission critical data centers running off 24 12V in parallel and serial (several Amper-Hours at 24V) transformed to 220V.

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The Zener diode in those battery chargers is used as a voltage reference. The constant voltage is then used with a potentiometer for manual adjustment of the set value for the battery voltage. –  Peter Mortensen Aug 4 '09 at 10:44

I have one computer that has a power supply that says it will work off of a DC power source, unfortunately it requires over 110 VDC, to power it.

One thing that I found particularly wasteful, was a Laptop, on a cart, with it's charger plugged into a UPS. Which means it took 110 VAC, converted it to ~12 VDC, converted that to 110 VAC, converting that to ~19 VDC, and then finally converting that to ~12 VDC, 5 VDC, and 3.3 VDC, and using the 12 VDC to power the back-light. Talk about stupid. It also had a separate keyboard, and mouse, because the only part you could get to was the screen.

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Talk about indirection! –  voyager Aug 4 '09 at 1:29

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