[SOLVED] Building a portable, battery-powered mini PC ?

[Dynam0]

As the title says, i want to build a custom mini pc. The reason i'm not buying just a laptop or a mini pc are many...First of all i want something that will be able to be upgraded in the future without problems, that's why i'm putting a Micro-Atx inside instead of a laptop mobo. 2nd i want portability without interrupts (the reason for a backup battery inside ).

I have already think almost everything, but i'm struggling on finding a solution to switch from power-brick to battery without the pc to shut down in the "transfer time". I'm thinking of a ups 12v dc board (like the router ups) but the 10-12ms transfer time looks too much for me.

I have no problem to manually turn a switch instead of automatic switch when i unplug the brick from the laptop though,so if you have any manual uninterruptible switch like suggestions are more than welcome.


In the sketch (url) below is the diagram i have in my head since now

https://imgur.com/a/z9KNSjo

View: https://imgur.com/gallery/z9KNSjo

 

[bill001g]

You do this the way true online commercial UPS do it, you in effect always run on the battery. These devices always convert the power to DC and then back to AC unlike the cheaper UPS that just pass the city ac power through and then switch to the battery.

It is actually much simpler because you are not trying to convert the power back to ac. Without a complicated explanation if you connect the incoming dc power to the battery and to the pc at the same time it will in effect pull power from both all the time but because the city power has unlimited capacity it will also constantly recharge the battery.

As long as your incoming power supply has enough capacity to run the pc as well as charge a drained battery at the same time you should be fine.

Note this is for your more simple lead acid batteries. Lithium batteries can work similar, I mean your cell phone does it, but these take very special charging circuits.

.....so after looking at your diagram you are talking about lithium. I would just stick a properly sized diode in between the battery pack and the direct dc to prevent it from feeding back to the battery pack output.

 

[Dynam0]

First of all thanks for the help! The way you are suggesting seems pretty simple though my worry is, will the bms module deliver the power to the system right? I heard that commercial ups and laptop control modules are pretty complex to achieve the "constant power feed" result by charging and discharging the battery the same time.

 

[bill001g]

With simple batteries this just works. It sorta does charge and discharge at the same time but unlike lithium batteries the batteries themselves are limiting the charge.

If we take a more simple case where you have external dc power to the battery pack and you hook a output load like a pc to this what does the BMS do. Does it somehow block the output or does it just shut the charging off.

Maybe if the BMS is smart enough you do not need the second connection. This is hard to say you basically have a computer in the path.

As long as you blocked power being feed into the output I can't see how the BMS would know the second power source existed. The dc power from the city likely would be slightly higher voltage and the pc would draw most the power from that.

 

[Eximo]

I would just get a 12V input motherboard and simplify the components list. Particularly if you are going all NVMe storage there is no need for internal 5V and 3.3V. GPUs run on only 12V if you are looking at getting a GPU.

You could actually adopt one of the few available 12VO motherboards. There are also plenty of 'non-standard' motherboards with DC input. Usually Mini-ITX designed for automotive or other purposes.

If you are just after a desktop PC that you can power off the grid, there are plenty of heavy duty power banks on the market now. Bit expensive though. Then again, so is a pile of 18650 cells with enough power to run a desktop for more than a few minutes.

Just remember, you are only likely to get one or two major upgrades into a PC before other things are going to start looking better.

 

[Eximo]

You could look at a 12V Lithium replacement, again, quite expensive. But then your charger can be a relatively dumb one, and the charging circuitry will be in the battery.

Or any NUC or similar system that runs off a power brick. Then you just match the voltage and bypass the AC input, let it take care of itself.

I've had my eye on Intel's latest NUC with the system on a card concept. The latest 12th gen is even socketed so the CPU can be replaced. And the other slot is for any x16 expansion card you could want to install.

 

[punkncat]

I find myself a bit curious about your battery choice. You realize that these are ~3000mAh at the top of the line. 15A discharge providing from 4.2 to 2.5VDC at cut off. Even using a large sized pack of these is not going to provide power for a 'desktop' type system for very long. They are just about the same size as an AA battery.

This design is also not making allowances for how you are going to power a monitor. Certainly, the combined load of a desktop system and a monitor is going to result in a very large battery pack. Along with your design spec of using a mATX the system itself is going to turn out to be fairly bulky.

Considering the speed at which systems become obsolete along with your need to stay within very low power hardware it would seem to me that the 'upgradability' is going to time itself out very quickly....which leads back to cheap laptop IMO.
Obviously, I don't know what your use case is. If the project is just a 'see if you can do it' I applaud the effort and would be anxious to see what comes of it. If it is to try and get an actual usable run time without AC power...not so much, but I could well be wrong.

 

[Dynam0]

I think i will stick with the constant charge of li-ion batteries on a low voltage (trickle charge but below max charging voltage. Seems to me the best way to go until now. Also, i'm not intend to use it a lot with the batteries, mostly it will work with power brick on. As for the monitor, off the main desk use i will have a portable 12v monitor from an old laptop powered from the batteries like the PicoPSU.

But i think i will open a new thread talking about other solutions instead of the picoPsu. I don't really want to stress this little board to it's limits. It can support up to 8-10amps safely through the +12v meaning that with a power thirsty cpu or a ryzen G i will face problems. I would like to add a SFX Psu but haven't realised yet how can i power it with batteries too