Concept: battery backed up PC ATX power supply - Page 1
Forum section: electronics / general

author: VinzC
author_rank: Frequent Contributor
timestamp: June 19, 2019, 07:05:45 pm
content: Hi all.I do have a UPS for my computer and equipment. What I'd like is to combine UPS features with a traditional PC power supply, i.e. the main circuit would be designed like a car PC PSU to draw power from 12V batteries but for home, not automotive use. The PSU would be powered from the grid and only from the battery in case of mains outage.I know this sounds like an uninterruptible power supply such as MGE's but the concept I'd like is different. A traditional UPS is an inverter that outputs mains voltage and uses the battery for backup. I find it silly to go from low to high voltage and then to low voltage again just because the PSU input is mains when everything works with 12V max...What I'd like is to eliminate that inverter stage and use a single but high power 12VDC source to output the voltages required for a computer (+/-5V, +/-12, +3.3V), like a 300W PSU would. And to that the power supply would use the mains power to charge the battery when needed but would supply a unique, high-current 12V.Do such power supply units exist? (I'm asking because I have found none so far.)

author: Benta
author_rank: Super Contributor
timestamp: June 19, 2019, 07:14:30 pm
content: Quote from: VinzC on June 19, 2019, 07:05:45 pmNo. They make no sense and would have duplicate a lot of the circuits in the existing ATX supply.

author: VinzC
author_rank: Frequent Contributor
timestamp: June 19, 2019, 07:22:52 pm
content: Quote from: VinzC on June 19, 2019, 07:05:45 pmQuote from: Benta on June 19, 2019, 07:14:30 pmI think you didn't get my point: the purpose is to *replace* the traditional PSU, no to plug to it so of course they make sense.Quote from: blueskull on June 19, 2019, 07:19:02 pmThanks for the link. However I see none that would embed a battery backup. Do you have an item as a reference?

author: Siwastaja
author_rank: Super Contributor
timestamp: June 19, 2019, 07:38:21 pm
content: Now as li-ion has been cheaper, more robust, and better in every imaginable way for years already, it would be weird to design anything around the 12V lead-acid voltage anymore. 3s li-ion is close; but neither 12V LA or 3s li-ion matches the ATX spec anyway, so does it matter?Looking at both simplicity and efficiency, I would like to eliminate all redundant power conversion steps. I bet most 12V PC stuff would work just fine with significantly larger voltage range, as the 12V is just a completely arbitrary voltage and is locally bucked down to several voltages, highest of which tends to be around 5V, and most power is consumed in lowest (around 1V) core supplies.Of course it would violate the ATX spec, but it could be interesting to try tying a 3s li-ion pack to the "12V" line. The cells would float at 4.00V/cell, which is quite acceptable at around 80% state of charge. At about 20% state-of-charge, the pack would be around 10.3V, which shouldn't pose any actual problems, unless a specific device monitors the input voltage too eagerly, being "too smart" against out-of-spec ATX 12V. This would need to be tested.Generating the required 5V/3V3 lines would be a walk in the park, as they tend to be low-power lines, and accepting one extra conversion step for them wouldn't be an issue. Most of the power would run with zero extra conversions compared to a non-UPS system.For this to work, the standard ATX supply would be replaced with one that can support CC operation without faulting, for charging the battery after the outage, and small buck converters added for 5V,3V3 low power supplies. Apart from the battery itself, the cost and complexity is about the same to a bog standard non-UPS ATX supply.This is basically how laptops internally work. I'm 100% positive something like this is used in some server hardware, as well.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 19, 2019, 07:39:22 pm
content: I have done a few DIY designs of that type. Pretty much I just devise a way to get regulated 12V from either battery or mains and use DC/DC converters for the rest. Here's the first one I did, still working great after about 7 years of service:

author: orion242
author_rank: Unknown
timestamp: June 19, 2019, 07:50:37 pm
content: Why not use a 12v ATX power supply and just keep the batteries topped off via mains. Pretty sure 12v ATX power supplies are readily available.

author: Red Squirrel
author_rank: Super Contributor
timestamp: June 19, 2019, 08:18:36 pm
content: What I'd like to see is PSUs that take 48v as input. Then you just have a single large 48v battery bank on float with DC breaker panels and distribute power that way. Just like telco gear. They DO make them but they are very hard to find.I've found when it comes to this stuff it's easier to just have an inverter setup and run everything at 120vac. Like in my solar shed I did everything 120v. It's just easier as 120vac stuff is readily available. Switches, breakers, fixtures, pretty much any device imaginable etc.I had toyed with doing my server room all 48v but trying to actually find 48v stuff as a consumer is very hard. You can't just order that stuff of Tigerdirect or Newegg etc and hardware stores won't have anything of that nature either such as breakers and so on. So when I do upgrade my setup I will do 48v, but straight to a pair of inverters which will then power the PDUs. That way everything after that is going to be standard gear. There is more power conversion involved though so it is a bit less efficient.I eventually want to get into playing with lithium or LIFPO4 batteries too but they are harder to find and more expensive. You also have to filter through all the fakes. So sticking to lead acid for now. It is still king in these applications. I think that will slowly change over time.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 19, 2019, 08:43:27 pm
content: Quote from: Red Squirrel on June 19, 2019, 08:18:36 pmYou could do HVDC at 170V or 340V, which works with standard PSUs and is also trivial to derive from mains with a simple rectifier. DC rated breakers and switches are a little hard to come by but easier than before thanks to the popularity of solar power. Trapezoidal wave AC and pulsed DC are also worth looking at.

author: mariush
author_rank: Super Contributor
timestamp: June 19, 2019, 09:10:26 pm
content: Problem with low voltage is the current and high losses due to wire resistanceYou have a pc peaking at 3-400 watts... that's 30+ A ... you'd need a bunch of thick wires between psu an pc.There's also issue of power stages / mosfets being optimized for ~12v ... with 48v in, you'd have a hard time designing cpu and gpu vrmsI'm of the opinion that standardizing around 20v +/- 5-10% would make sense... 20v is usb standard voltage, we already have laptops using 16.5v .. 19v adapters so mosfets and ICs exist to run directly with 20v , 18v..22v means low volume cheap easy to make polymer capacitors can be used and not least it's considered a "low voltage"... and good compromise (can make itx systems that use <65-90w powered from 19v barrel jack or usb 20v or thunderbolt for example power pc from monitor's psu or could have 1000w psu with loads of 4pin awg16 20v connectors (each good for 10-15A or ~300w each)So a new revision of atx psus could add 20v , make 12v less important (fans - but 24v fans can work just fine with 20v so could just relabel as 20v or re-engineer for 20v, mechanical drives, rgb crap, backwards compatibility with video cards) and 5v could remain for usb and other things. Could make stand-by 12v or 20v as well, for higher efficiency. Drop 3.3v and -12v ... a dc-dc converter on mb can produce 3.3v for m.2 and pcie slots, cleaner, in small area, and no need for 4+ pairs of 3.3v+gnd wires in 24 pin conn. for it.Could have power supplies made with alternate dc in (24v) ... 2 lead acid batteries in series give you ~20v..26v... enough for dc-dc converter inside to produce clean 19..20v (20v +/- 10% would allow min 18v)I think one could even add 20v to pci-e by adding an extension (like they did with agp pro), backwards compatible.

author: rrinker
author_rank: Super Contributor
timestamp: June 19, 2019, 09:10:49 pm
content: This is (and has been for a long time) been done in telcom, where +/- 48VDC was common. I remember getting a tour of a then new fiber node which had racks of 48V equipment and the power supplies included the batteries, they didn't take in 120VAC, and output 120VAC to yet another stepdown to 48VDC, they took in 120VAC and output +/- 48VDC.Several PC makers offer rack mount servers with a 48V power supply option.here have also been PC power supplies that incorporated the UPS. The 48V was a compromise, needed for the telcom ring circuits but also not so low as to need really heavy cable. You try to run no more than 12V DC in server racks and you will need some really thick cable to avoid voltage drop.

author: wraper
author_rank: Unknown
timestamp: June 19, 2019, 09:22:00 pm
content: Quote from: VinzC on June 19, 2019, 07:22:52 pmThe thing is, it would be the same as connecting 2 separate PSUs in parallel unless you power it from 100+V of batteries. In such case it would be much easier to do.

author: Red Squirrel
author_rank: Super Contributor
timestamp: June 19, 2019, 10:00:22 pm
content: Quote from: NiHaoMike on June 19, 2019, 08:43:27 pmWas thinking that too actually. Need way more batteries/cells to form a string mind you, but it would be overall more efficient too. May need to modify some PSUs just to make sure the hot/neutral pins are all matching positive/negative but other than that it should in theory work. Could use standard power outlets and cords too I think. Just not switches or breakers as arcing would be an issue.

author: VinzC
author_rank: Frequent Contributor
timestamp: June 19, 2019, 10:05:29 pm
content: Well, first off thanks to all for your insights.The idea comes from having seen car PC power supplies, likethis oneorthat one. For having used one in a car PC, I know some do work. Of course the one I tested was powering just a motherboard alone without an external video card but you get the concept. Since there are also 12VDC power supplies (SMPS connected to mains) of various peak current, combining the two with a battery and charger should be possible, that's what I thought.Note that I don't necessarily want to stick to 12V or 300W — I have to measure the peak power consumption of my equipment beforehand. Two batteries in series would do as well. I'd just like something that would avoid going to then from high voltage.BTW, by the law of conservation of energy, upping to 220V (or 110V) should be no different than straight from the battery, right? The inverterdraws the same amount of power from the battery even if it outputs mains voltage, right? So, yes, that'd imply using thick sections. For having worked in a company that makes its business from stretching luxury cars (which implies cutting and stretching power cables), I've seen some big stuff from the automotive industry.The thing I don't know is how stable the 12V line must be and what its voltage swing it shall be for a PC motherboard.Kudos to NiHaoMike for the pics. That looks messybut *very* interesting. Do you share the schematics?EDIT:I also forgot... I'd also like to stay away from lead-acid batteries as the place I'm thinking of putting my power system is not well ventilated, i.e. no straight path to the outside walls.

author: windsmurf
author_rank: Frequent Contributor
timestamp: June 19, 2019, 10:11:11 pm
content: See:http://www.nipron.com/dc_ups/dc_ups/

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 19, 2019, 10:22:02 pm
content: Quote from: Red Squirrel on June 19, 2019, 10:00:22 pmProbably would make more sense to use DC/DC converters from lower voltage batteries unless you're dealing with very high power levels.

author: VinzC
author_rank: Frequent Contributor
timestamp: June 19, 2019, 11:33:20 pm
content: Quote from: windsmurf on June 19, 2019, 10:11:11 pmSo they exist!

author: wraper
author_rank: Unknown
timestamp: June 20, 2019, 01:35:20 am
content: Quote from: VinzC on June 19, 2019, 11:33:20 pmAnd their efficiency spec is so piss poor that even running a good standard ATX PSU from half decent UPS or inverter will be more efficient. Not to say efficiency during normal operation.

author: David Hess
author_rank: Super Contributor
timestamp: June 20, 2019, 03:51:52 am
content: They used to make ATX power supplies like that. They had a lower intermediate voltage which was the same as the backup battery's voltage so essentially they were a online UPS combined with a power supply.The easiest way to do it now is probably to use one of those 12 volt input power supplies intended for low power systems with a battery and 12 volt power supply/charger.

author: dzseki
author_rank: Frequent Contributor
timestamp: June 20, 2019, 06:38:44 am
content: It depends on your power needs. There is a thing called "PICO PSU" which is a small DC/DC convcerter that plugs right in the ATX connector of your mobo. All it needs is a 12V input, the output power is limited though: 120-160W I think. But with that you are almost done.

author: VinzC
author_rank: Frequent Contributor
timestamp: June 20, 2019, 09:02:43 am
content: Quote from: windsmurf on June 19, 2019, 10:11:11 pmQuote from: VinzC on June 19, 2019, 11:33:20 pmQuote from: wraper on June 20, 2019, 01:35:20 amQuote from: blueskull on June 20, 2019, 05:04:50 amWoah, guys, wait. It's only about someone here (whoever it is doesn't matter) claiming such PSU's don't exist and make no sense. Someone else (whoever it is doesn't matter) responded with a link to an actual reseller, making the point and that's it. The rest (about efficiency et al.) is something else. If there's one supplier for such power supply units, logically then there must be others. That's the point. All I have to do is find a good one.There's still some good power supply to find given my equipment's consumption. There is also building one, just like NiHaoMike did if none fits. Such kinds of PSU's deserve to exist IMHO, there should be more.

author: David Hess
author_rank: Super Contributor
timestamp: June 20, 2019, 04:14:31 pm
content: These looks similar to the ATX power supply which included battery backup that I remember:https://www.sunpower-uk.com/product/atx-power-supply-with-ups-function-2/https://www.trumpower.com/medical/mpc.htmlhttp://www.nipron.com/dc_ups/dc_ups/One of the interesting features of the one I remember was an innovative thyristor based inverter which allowed the ATX power supply to also supply AC backup power to the monitor. This was almost pre-internet so good luck trying to find it.

author: tooki
author_rank: Super Contributor
timestamp: June 21, 2019, 12:02:16 pm
content: Years ago, google stopped buying off the shelf motherboards and began having them custom built, and one of the modifications they did was to have direct 12V DC input plus a direct battery input on the boards instead of using AC PSUs and UPSes:https://www.nytimes.com/2006/09/26/technology/26google.htmlBut it looks like more recently, they’ve begun moving to the 48V telecom standard rrinker mentioned:https://datacenterfrontier.com/google-unveils-48-volt-data-center-rack-joins-open-compute/

author: jmelson
author_rank: Super Contributor
timestamp: June 21, 2019, 08:56:19 pm
content: Quote from: VinzC on June 19, 2019, 07:05:45 pmPico PSU makes some power supplies for mini-ITX motherboards that run off 12 V DC and other voltages. These are for lower-power machines, not the top of the line gaming monsters. The entire PSU is a little PC board that plugs into the motherboard power connector, and has a few cables dangling for the hard drive and CD drive.Jon

author: Stray Electron
author_rank: Super Contributor
timestamp: June 22, 2019, 12:30:54 am
content: Quote from: orion242 on June 19, 2019, 07:50:37 pmI was going to say the same thing. I picked up a bunch of embedded computers that had 12VDC power supplies that look like these from E-bayhttps://www.ebay.com/itm/Pico-PSU-120-12V-120Watt-DC-DC-ATX-Power-Supply-for-Mini-ITX-Mainboard/333192561048?hash=item4d93d30198:g:Z3QAAOSwfz9c1y7e. I can't say if the E-bay ones are any good but the ones that I have look identical and came from a very demanding commercial application and I haven't found a bad one yet. These plug directly onto the ATX power connector, connect 12 VDC to the input and away you go. They also have a cable with connectors to power the hard drive and floppy drives.

author: windsmurf
author_rank: Frequent Contributor
timestamp: June 22, 2019, 12:34:22 am
content: Quote from: Stray Electron on June 22, 2019, 12:30:54 amCould this be adapted to work off both AC as well as battery, effectively making it a UPS setup?

author: Stray Electron
author_rank: Super Contributor
timestamp: June 22, 2019, 12:47:29 am
content: I don't see any reason why not.

author: AFriendlyFish
author_rank: Newbie
timestamp: September 08, 2025, 12:49:29 pm
content: Following up 6 years later as most of the original links are broken and I still don't understand how to use the knowledge in this thread for my application.Is there a way I can power an eGPU rtx 4060 with a 25.6V or 12.8V LiFePO4 battery? I don't think I can connect the batteries directly to the GPU right? Probably I do have to do some type of conversion, but I'm really struggling to find a battery to eGPU power supply converter and I think that's because I lack the knowledge to even do a competent google search rather than the products don't exist.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 08, 2025, 03:23:02 pm
content: Easiest by far is using inverter (24V or 12V nominal) with mains voltage output, then usual ATX power supply. That way, you can also power your monitor and other potentially important loads.

author: nctnico
author_rank: Super Contributor
timestamp: September 08, 2025, 03:43:30 pm
content: There are ATX power supplies with DC inputs. Random google find:https://www.mini-box.com/M4-ATXA lot of monitors come with external power bricks nowadays to have 19V DC. So a 12V or 24V to 19V adapter should work to get the monitor going.

author: VinzC
author_rank: Frequent Contributor
timestamp: September 09, 2025, 01:05:11 pm
content: Quote from: AFriendlyFish on September 08, 2025, 12:49:29 pmThread hijacking, huh?(not to mention necroposting...)Quote from: Siwastaja on September 08, 2025, 03:23:02 pmThat isEXACTLYwhatIwanted to avoid. See the initial post.Quote from: AFriendlyFish on September 08, 2025, 12:49:29 pmThis setup requires some DC-DC conversion and there are off-the-shelf devices to do exactly that. However, if/since you're not familiar with electronics development, I would not recommend a DIY solution as it's not really straightforward. These GPUs tend to draw a lot of energy, so extreme caution is essential here.

author: coromonadalix
author_rank: Super Contributor
timestamp: September 09, 2025, 02:32:01 pm
content: Quote from: AFriendlyFish on September 08, 2025, 12:49:29 pmhave you tough of : if it doesn't exist it's not worth the hassle, the added complexity, the power losses or else ? yeah you do have 19vdc small sff pc or lappy, or external monitors, powering beast gtx 4k or 5k, series who suck 200 300 400 500 or 600w and higher ?? you dont get the maths to do soyou do have ac to dc supplies and ac in - dc in to only dc out supplies, i have a few but it is not made to power huge rigssome ups have limited working life on battery, unless you go with huge capacity packs you wont get 4 -8 hours of use ?you do have mini / micro atx psu's up to 240watts for car related pc's from 12 or 24vdc batteries, but they don't have tons of output connectors,once again it is not for high power video cards

author: AFriendlyFish
author_rank: Newbie
timestamp: September 17, 2025, 01:58:49 am
content: I think some of these more modern GPUs have power requirements below 200 Watts. Specifically for the full size RTX 4060, the gpu is capped at 150 Watts.

author: amyk
author_rank: Super Contributor
timestamp: September 18, 2025, 03:57:42 am
content: Here's a few more, search keywords are "ATX UPS":https://us.misumi-ec.com/vona2/detail/110400088760/http://www.indocomp.com/IND-UPS200-ATX.htmlhttp://apollo.com.tw/edcontent_d.php?lang=en&tb=2&id=117http://topmicro.com/UPS.phpThey won't be very high capacity; enough power for several minutes to allow an orderly shutdown is their intended use.