I think we need the following internal UPS product:

  • Can be fit to 5.25 drive bay (like optical drive).
  • You connect PSU to this UPS with standard 24 PIN PC Main connector + other connectors for additional power (P4, Peripheral connectiors, etc.).
  • You connect motherboard and peripherals to this UPS with standard 24 PIN PC Main connector + other connectors (P4, Peripheral, SATA etc.)

This way this UPS does not need to very inefficiently generate AC power like in classic UPS but straight DC power for motherboard - just like a laptop battery pack. I think this inefficient battery - DC - UPS - AC - power supply - DC - motherboard conversions is a cause that a heavy UPS can only support a PC for a couple of minutes but light laptop battery can be used for hours.

Anybody heard of a product like this or is in the position to create one?

  • 1
    This sounds like insanity.
    – Chopper3
    Feb 28, 2012 at 11:53
  • 2
    @nhinkle - why this is put on hold / closed? This is not a product recommendation question and it won't be obsolete in foreseeable future. This is a more like question "Why everybody does it in this, not optimal, way?"
    – Tometzky
    Jul 17, 2013 at 9:25
  • I'd mostly be interested in something that could hold me over for the 30-60 seconds it takes to save and do a clean shutdown. A bank of supercapacitors could probably hold that much. Apr 2, 2015 at 23:49
  • globalsources.com/gsol/I/Online-UPS/p/sm/8808126729.htm
    – user329172
    Jun 17, 2019 at 17:40
  • @blueray This is not the thing. This is just an ordinary 110V/220V AC UPC, but in 5.25" case. I was rather talking about a much more efficient 3.3V/5V/12V DC UPC sitting between the power supply and the motherboard.
    – Tometzky
    Jun 18, 2019 at 14:12

4 Answers 4


My company have just designed a ups as you have described it. Our ups sits between the PSU and the motherboard and we have managed to drive an i7 CPU pc with 2 HDD's and monitor for 2 Hours. We have a USB connection to the pc that controls the ups and shows status etc. We can extend the ups up time in increments of 2hours in addition to the internal battery in the 5.25" ups.


Well, not directly, and i don't see a battery of any significant capacity being that small.

Now, if you COULD get a battery that small - you could possibly use a board like this or this which seems to be designed for low voltage systems. They're designed for car use, so you'd need some form of lead acid battery - too large for your use

There are 12V lipo batteries, but they arn't the same as 12V lead acid batteries, so would have a different charging circuit, and other changes. The design you want would be a combination of something like the above and the one below.

Laptops don't only use less power due to the conversion tho - you could easily build a PC with laptop parts - for example, there were MANY mini itx boxes with pentium M processors.

Desktop PCs have less design compromises - they run hotter and faster both at the processor and peripherals. They have faster and larger hard drives. Its a little like saying that your little british three wheeler is better than a bugatti veyron cause it uses less fuel, and this is cause the bugatti has a excessively large fuel tank.

  • But laptops do not use orders of magnitude less power than a PC. An idle Sandy Bridge system can use about 30W at the plug, on extreme load it peaks at 90W. And this is with inefficient power supply. My laptop battery (170cm3 300g) is rated at 55Wh, which would be enough for almost 2 hours of idling system, half an hour under load. And there's over 1100cm3 volume in standard 5.25' bay (6.5 times more).
    – Tometzky
    Feb 28, 2012 at 14:42
  • Not all UPS is battery...
    – HaydnWVN
    Feb 28, 2012 at 15:59
  • My sandy bridge laptop uses around 9 watts. If you had a 'desktop' built around a ULV processor, integrated graphics, and a regular PSU designed for 80+% power efficiency at the power you will be drawing, it'll use less power than say, a core i7 laptop. In addition idle power isn't a good metric. If you're not going to be using your system you might as well have it switched off.
    – Journeyman Geek
    Feb 28, 2012 at 23:43

There was (is?) something available that fits in to 5.25in bay - here, here and here

  • 1
    Yes but all this are just normal UPS'es in 5.25' form factor - they generate normal 230V/ alternating current - like from a wall socket. It is extremely inefficient, as PSU will have to convert it back to 12V/5V/3.3V static current for motherboard.
    – Tometzky
    Feb 28, 2012 at 14:28

Seems like a good idea, if you would use an external battery. Also most people will want to also connect other equipment like a switch, router, monitor. It is not (easily enough) possible to do this utilizing only DC-DC.

  • A monitor I bought recently, LG IPS234V-PN, uses external power supply, which provide DC - like a laptop. It would not be hard to provide power from internal power supply also for the monitor.
    – Tometzky
    Dec 21, 2012 at 6:49

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