Powering a PC's PSU with 12vdc input, rather than AC

[harrisonpatm]

This is just for an idea I had that I wanted to experiment with, non-critical.

I want to play around with using scrap PC parts to build a low-cost NAS for my family, just for fun to see if it can be done using free or dirt cheap parts off Facebook Marketplace. So far I got a free PC with 6 SATA ports, two free 4tb HDDs, and I'm spending less than $20 on extra connectors from Aliexpress and a small SSD boot drive from Ebay. I like projects that actively use up what would potentially be ewaste.

Thing is, much of my house runs off my homemade solar power system, 48vdc nominal. I extensively use several small 12vdc converters to power a lot of things. What I'd like to look into is the possibility of powering this NAS PC off DC directly, so that I'm not adding to my electric bill. Normally, the advice is to use an inverter to bring my 48vdc up to 120vac, plug in the PC's PSU, which brings it back down to 12, 5, and 3.3vdc.

Instead, I'd like to consider how to power the PC directly off DC, using a 48v to 12v converter. In my googling so far, I came across this video, where this guy with the most amazing accent ever is dissecting an old PSU. At 26:40, he backfeeds 12v into one of the 12v rails, which surprisingly brings up all the necessary voltages to the rest of the PSU. That would be cool if I could just do that. Has anybody else here tried that? If I try that, am I gonna fry the motherboard? Maybe I should keep an eye out for a second free crappy PC on marketplace, just to experiment with whether that would work, before I try it on the board that I'm planning on keeping.

 

[thepronghorn]

I'm also interested in this, but I haven't tried it yet. It seems like it should work.

 

[LewTwo]

Points of interest:
most laptop PC'c run off 18 VDC power supplies.
many MiniPC's run off 12 VDC power supplies.

I have in my hand a Terryza minipc model GK3V that requires a 2.5 Amp 12 VDC power input.
It has a 1/2 TByte interna 2.5 inch SSD, 8 Gbytes of Ram and Intel Celeron J4125 CPU.
It also has 2 USB-2 ports and 2 USB-3 ports which could have external USB drives attached.
This is an older unit but the main point is it only requires 12 VDC power.

 

[harrisonpatm]

Points of interest:
most laptop PC'c run off 18 VDC power supplies.
many MiniPC's run off 12 VDC power supplies.

I have in my hand a Terryza minipc model GK3V that requires a 2.5 Amp 12 VDC power input.
It has a 1/2 TByte interna 2.5 inch SSD, 8 Gbytes of Ram and Intel Celeron J4125 CPU.
It also has 2 USB-2 ports and 2 USB-3 ports which could have external USB drives attached.
This is an older unit but the main point is it only requires 12 VDC power.

All good info, and the two computers that my wife and I use are laptops, which run off either 12v or 5v directly. So no issue there.

For the DIY-scrap-free-salvaged NAS that I'm thinking about, I want to use what's available, which in this case was a standard PC that I got for free. Besides, basic PCs and PSUs that power them are fairly common, so I opened the thread in case any useful information can make its way to other people interested.

A super complicated and inefficient idea that I had, is to purchase 3 separate DC-DC converters, all from 48v input. One at 12v, one at 5v, one at 3.3v. Then manually solder into the PSU wires with the appropriate voltages. It's not a great idea, as it involves purchasing 3 separate components, dealing with 3 separate conversion inefficiencies, and it doesn't address negative voltages that the motherboard may need. So I won't do that.

 

[Gruesome]

Alternatively, scrap the free PC, and attach the hard drives & SSD (via a USB hub, if necessary) to a Raspberry Pi that you set up to run headless (no keyboard nor display). Then I think all you need is 5V, maybe 12V for the disk drives. A regular PC draws unnecessary power, plus the power supply is often the weak link, so you don't want to skimp on that.

The more recent Raspberry Pi's (4 and 5, or similar single board computers) need a good relatively beefy 5V supply, >2.5A, so probably should not be just powered from a USB hub. The latest RPi 5 has a recommended 27W supply that supposedly allows to power peripherals from the four built-in fast USB sockets, so you could skip the USB hub.

 

[harrisonpatm]

Both also good suggestions, but the point is to use the scrap that's available to me, which is a desktop PC.

I actually don't mind keeping total power drawn down. I don't want it to be massive, but I currently have an overproduction of solar, and have excess energy to go around.

 

[Gruesome]

Well, then there's this stuff made for 48V: Catalog of 48 volt or -48 volt DC Input PC ATX Computer Power Supplies, 48 volt Input for server farms, telecommunications rooms. autonomous vehicle computer power, fully isolated, 48V ATX PSU, 48V , ATX DC-DC I have no idea how reliable these are.
It's just that a reliable PC power supply in my experience costs a multiple of a Raspberry Pi with power supply.

 

[harrisonpatm]

Well, then there's this stuff made for 48V: Catalog of 48 volt or -48 volt DC Input PC ATX Computer Power Supplies, 48 volt Input for server farms, telecommunications rooms. autonomous vehicle computer power, fully isolated, 48V ATX PSU, 48V , ATX DC-DC I have no idea how reliable these are.

Ooo thanks, haven't seen those before. Too expensive, but maybe I can find an eBay discount

 

[harrisonpatm]

Well, then there's this stuff made for 48V: Catalog of 48 volt or -48 volt DC Input PC ATX Computer Power Supplies, 48 volt Input for server farms, telecommunications rooms. autonomous vehicle computer power, fully isolated, 48V ATX PSU, 48V , ATX DC-DC I have no idea how reliable these are.

Ooo thanks, haven't seen those before. Too expensive, but maybe I can find an eBay discount

 

[thebes]

I think the ideal solution for you would be to pick up a pico psu and buck down the 48v to something between 12 and 30 volts as thats usually the input voltage for these. There is a couple different models but the most common one looks something like this

and can be had for less than 20-30 usd depending on the type/output wattage. If you need more sata power connectors you can get molex adapters for a buck or two.

I would at the very least recommend having at least some airflow directed at these as they can get pretty toasty, I put some heatsinks on mine and it runs much cooler.

There are also more beefy units that are larger but do 500+ watts, this is one from pico box that I used for a 1u low power server build some time ago, they do tend to be more expensive though and are probably not worth it for you since youre just running a couple hard drives and not much else.

 

[harrisonpatm]

I think the ideal solution for you would be to pick up a pico psu and buck down the 48v to something between 12 and 30 volts as thats usually the input voltage for these. There is a couple different models but the most common one looks something like this
View attachment 358690View attachment 358689
and can be had for less than 20-30 usd depending on the type/output wattage. If you need more sata power connectors you can get adapters molex adapters for a buck or two.

I would at the very least recommend having at least some airflow directed at these as they can get pretty toasty, I put some heatsinks on mine and it runs much cooler.

There are also more beefy units that are larger but do 500+ watts, this is one from pico box that I used for a 1u low power server build some time ago, they do tend to be more expensive though and are probably not worth it for you since youre just running a couple hard drives and not much else.
View attachment 358691

Thanks, haven't heard of those before, I'll look into them

 

[harrisonpatm]

Eh, I eventually broke down and found another old computer for free and did some tests. Didn't work backfeeding 12v into the PSU. It looks like when you do that (at least on the 2 different PSUs I tried), you can successfully get 12v, 5v and 3.3v to all of the correct pins... but not the -5 or -3.3v. Which for booting the motherboard is important, I guess, because on two different mobos I tried, neither would boot.

Oh well. It was worth a shot, and didn't damage either motherboard.

 

[LewTwo]

Back in the day there were a few companies that manufactured 'drop in' 12 volt DC power supplies to replace AC power supplies in servers. They were targeted at commercial customers that needed their primary servers to run 24/7 regardless of the reliability (or lack thereof) of the mains service of the local power companies. The idea was to power these machines from battery banks that were constantly charged from the mains (i.e. a true UPS). I doubt you could find one today as it is not a concept that our friends in South East Asia decided to copy.

I stand corrected ... I just saw Guessome's post regarding the 48 Volt ATX supplies. Seems they have 12 Volt imput supplies as well ... but as you said, a bit on the pricey side.

 

[rafalg]

Maybe a good candidate would be some terminal computer (HP T620, T630, Dell Wyse) - they run off 20V DC and can be found really cheap. With some tinkering you can connect a disk or two. But it needs to be checked if they can run off any DC input, or need a dedicated power supply. Otherwise this pico-psu dongle looks quite interesting for low power stuff (and if you need to run more 3.5inch hard disks, just give them a separate 12V power supply)

 

[smitty2k1]

I have multiple PCs powered off 12v PSUs. As shown above there are nice little plug-in boards for it. Here is a deep dive thread: Power Supply - A Guide to 12V PSU

I'm not sure the specs on your homemade system but PCs are pretty sensitive to ripple, and that's one of the reasons you can't use super cheap LED PSUs.

 

[harrisonpatm]

Maybe a good candidate would be some terminal computer (HP T620, T630, Dell Wyse) - they run off 20V DC and can be found really cheap. With some tinkering you can connect a disk or two. But it needs to be checked if they can run off any DC input, or need a dedicated power supply. Otherwise this pico-psu dongle looks quite interesting for low power stuff (and if you need to run more 3.5inch hard disks, just give them a separate 12V power supply)

It's a good idea, there are lots of standalone home servers that just run off a 3amp 12v power brick. My reasons for trying to make it work on a standard PC are just because it was free and available. If I factored in the cost of purchasing a separate system that would make everything work of 12v, it would offset the cost of electricity used from powering a standard PC from 120vac. For me at least. Other people have different priorities.

In any case, I found a physical space in my house where I can just plug it into one of my outlets that's powered from my solar inverter. So it's still off-grid, running off free energy anyway.

I have multiple PCs powered off 12v PSUs. As shown above there are nice little plug-in boards for it. Here is a deep dive thread: Power Supply - A Guide to 12V PSU

I'm not sure the specs on your homemade system but PCs are pretty sensitive to ripple, and that's one of the reasons you can't use super cheap LED PSUs.

Thanks, I'm going to read through your link!

 

[Superb_Raccoon]

It's a good idea, there are lots of standalone home servers that just run off a 3amp 12v power brick. My reasons for trying to make it work on a standard PC are just because it was free and available. If I factored in the cost of purchasing a separate system that would make everything work of 12v, it would offset the cost of electricity used from powering a standard PC from 120vac. For me at least. Other people have different priorities.

In any case, I found a physical space in my house where I can just plug it into one of my outlets that's powered from my solar inverter. So it's still off-grid, running off free energy anyway.


Thanks, I'm going to read through your link!

One way to reduce ripple and also provide some backup: Feed the line in through a battery first. That will provide almost perfectly flat voltage as it smooths out power delivery. A large capacitor will do the same thing.