The Plus Side of External PSU - or, why DC to DC is a Game Changer for Solar

[treefroggy]

I live off grid, with solar powering a 12v battery array.

Anything AC powered, I have to use a sine wave inverter. This wastes about 30% extra watt hours.

Which is why I am at odds with PC consumers at large. LTT laments the use of external power supplies to make electronics smaller.

But what if I told you, internal Alternating Current PSUs are actually my kryptonite?

Laptops and the latest mini pc's that use external PSUs provide DC power to the device. I can very easily take DC power directly from my DC fusebox from my 12v system, adjust the voltage, and splice the connector to provide a highly efficient power supply to any of my devices. With my main driver PC, this is the difference between running out of power at 9pm, and possibly damaging my battery, or being able to run my PC all night long, even gaming into the wee hours of the morning no problem.

I did a lot of research on Mini gaming PC builds, but even the smaller ones seem to only use AC PSUs. The mini-est of gaming PCs is still a niche market, they have the DC input I crave, but they're all prebuilt, which is a waste of money, and limits my customization options... Which is lame.

 

Any of the PC Building veterans here understand my plight and know what I mean? Can you think of any off-kilter PSUs that would let me build a low-profile tower like the ones on LTT, but without sacrificing DC to DC efficiency?

So far most of the advice I get is "just get a gaming laptop".... But that's not ideal. I would be paying for a screen I'd never use, the footprint is wonky and just not ideal for my life. That's why I got the minisforum elitemini H13G, and, if I could afford the NUC Phantom canyon, that would be extra sweet.

But the point of this is that buying prebuilds like that is lame. Building a PC with discreet GPU is the way to go for me, if only there was a PSU with a nice little barrel jack 19v input on it......

I have never built a PC before either, but, I've done the research, I'm a fast learner, and it aint rocket science, so I have a basic understanding. But I may not know some of the obvious stuff those of you who've built your own before are aware of. Thanks for understanding

[Electronics Wizardy]

Look at pico psus. They take dc voltages as a input, and then give you the rails needed and other signals a atx psu needs, like the ps on connector. 

 

Here is a example. Lots of simmilar ones exist on the market https://www.amazon.com/RGEEK-Switch-24pin-Supply-Computer/dp/B071P3HMNK/ref=sr_1_4?dchild=1&keywords=pico+psu&qid=1624600015&s=electronics&sr=1-4

[Elisis]

30 minutes ago, treefroggy said:

I can very easily take DC power directly from my DC fusebox from my 12v system, adjust the voltage, and splice the connector to provide a highly efficient power supply to any of my devices

Loss exists and stepping up DC is either costly or not scalable in relation to power.

[Freakwise]

The thing about prebuild (or "full size" pc in general) was there's no dc dc power supply (yet) that more power than 400w-ish

But

There's one exists

 

Hd plex 800

https://hdplex.com/hdplex-800w-dc-atx-with-16v-63vdc-input.html

 

[mariushm]

You don't want to have cables carrying 12v DC through your house... you'll have huge losses. The higher the current, the bigger the losses in the wires, because Ohm's law : Voltage = Current x Resistance ...  so you can use the resistance of the cable and current to see how much voltage you're gonna see dropped.

 

So for example, let's  say a laptop consuming 120 watts which is 5 meters from the 12v supply and you put regular AWG18 wires (like the ones in your atx power supplies)/

AWG18 wires have 0.02 ohm per meter of resistance, and you have 10 meters of wires between the 12v source and pc, and you have 120 watts / 12v = 10A

So Voltage loss = 10A current x 0.021 x 10 meters = 100 x 0.021 = 2v loss  - so your computer will see only 10v

 

Also the power lost in the wires can be calculated with formula Power = Current²x Resistance = 100 x 10 x 0.02 = 20 watts dissipated in 10 meters of cable.

 

Most switching power supplies will also run on DC ... just has to be high enough DC. For example, a 90v ...240v switching power supply / laptop adapter / whatever will run at 90v x 1.414 = 120v DC so in theory, you could put 10 x 12v lead acid batteries in series and power stuff from them.

You'll still have some losses in the bridge rectifier inside the power supplies, but you won't have losses in the inverter.

 

This aside, you will find all kinds of travel adapters and chargers, which will run on 12v or 24v (for trucks), just have to look maybe in specialized places.

There's stuff like the picoPSUs but those typically don't do a lot of current. There's better than picoPSU power supplies out there, which can run on DC.

 

With the ATX12v0 standard, I'd like to see more budget/itx power supplies that use just the single 10 pin connector (and maybe the 4/8 pin cpu connector, though the 10 pin connector would be enough to power both cpu and a single pci-e slot)  AND also offer a 12v DC in .. this way they could power either from a 12v laptop adapter OR an internal atx12v0 power supply.

 

But I think their worry is that people would be stupid and plug 16..20v laptop adapter chargers by accident and damage the boards so they'd have to add extra protection circuitry or add a dc-dc converter to convert 16..20v down to 12v.

 

 

 

[akio123008]

3 hours ago, mariushm said:

You don't want to have cables carrying 12v DC through your house... you'll have huge losses.

Problem with that is, for most loads you'll use, those losses will actually be smaller than the losses in an inverter.

 

As an operator of a small off-grid system that runs on 12V, I've considered running everything on the 240V inverter, to avoid wire losses, but it turns out the inverter wastes more power than I'd save by running everything on 240V.

 

Now of course that does depend on a lot of factors, like the 12V wire gauge used, the inverter, the distances you need to cover, and the loads you attach, so it might be different for other people.

 

For larger off grid systems that operate at higher DC voltages (which is inevitable for higher power systems) you can use a normal AC power supply just fine. A standard ATX PSU will run fine on anything between 100-250V DC. (as @mariushm also pointed out.)

 

Also, if you really want to run a PC on 12V, you could try to rig up your own power supply. There's plenty of 12V adjustable DC converters you can buy, if you can make sure to operate that in the ATX spec, and attach some computer PSU cables to its output, there's no reason you couldn't use that as a power supply.

[treefroggy]

18 hours ago, Elisis said:

Loss exists and stepping up DC is either costly or not scalable in relation to power.

 

17 hours ago, mariushm said:

You don't want to have cables carrying 12v DC through your house... you'll have huge losses. The higher the current, the bigger the losses in the wires, because Ohm's law

 

14 hours ago, akio123008 said:

Problem with that is, for most loads you'll use, those losses will actually be smaller than the losses in an inverter.

I know what voltage drop is you guys. I build off grid solar systems.

My setup is in a van, not a house. I already have my DC fuse box with several 12V lines that I already did the math and got proper gauge cables. I'm already supplying power to my DC devices like my PC and montior, which are even on the same line.

I'm just asking about Power Supply Options for building a PC. I don't need y'all telling me what I'm trying to do is impossible, because I've already done it.

I just would like to build a PC rather than be limited to pre-builts.

It's ahead of the times, I'll admit. So most people aren't going to understand.

My PC is within 1 meter of my battery. At that point you may as well be saying a battery-powered device is impossible, lol. (did you know laptops exist?)

With my setup, I assure you "just using inverter" is not ideal. As I said in my above post, I already did this with many devices and the power savings are crucial.

 

@akio123008 Thanks, your suggestion is the best, I could just make a PSU using several different voltage adjusters for each required input for each different part of the PC, lol. That seems most likely..... Just.... could be a real headache, haha. But yeah, would be awesome. I'll definitely post here if I ever finish one!

That said, guess I'll build a low profile gaming PC just like any other, minus the PSU!

Thanks everyone who took this seriously and offered great advice!

[akio123008]

13 hours ago, treefroggy said:

I could just make a PSU using several different voltage adjusters for each required input for each different part of the PC, lol.

For an ATX PC, yes, but in a few years, we might be using ATX 12VO and in that case only a 12V converter would be required, the rest would be built into the motherboard.

[treefroggy]

7 hours ago, akio123008 said:

For an ATX PC, yes, but in a few years, we might be using ATX 12VO and in that case only a 12V converter would be required, the rest would be built into the motherboard.

See, I'm new to all this.

That sounds wonderful. You're saying it will have a 12v input? In that case, I don't need a converter at all, since 12v is the power supply I'm already working with. Onward to the future!

[mariushm]

No, 12v0 power supplies output only 12v ... the 10 pin connector that replaces the 24 pin connector has power_ok , power_on , 12v stand by , 12v x 2 , ground ...

 

So it would be easier to make something or buy something that accepts some dc voltage and produces that 12v and the power_ok and power_on signals the motherboard expects (a 5-10 cent microcontroller can do those)

 

It could be as simple as an adapter cable that has a barrel jack at one end and the 10 pin and 8 pin cpu connector at the other end.

 

[artuc]

On 6/26/2021 at 9:03 AM, treefroggy said:

I don't need y'all telling me what I'm trying to do is impossible, because I've already done it.

I just would like to build a PC rather than be limited to pre-builts.

They're explaining why it's not really available because it's a niche that's not done by most people.

 

Cabling cost isn't such a big deal for something small like a vehicle where you may need a few metres at most. As you scale up you see more and more issues with the large current and therefore even 24 and 48VDC used if for some reason DC is preferred/needed.

 

The assumption is most built desktop PCs will be in a house and the house will have mains AC, because that is the reality for 99.9% of use cases.

 

Laptops, NUCs and PCs specifically for industrial, AV, displays/POS, surveillance/security etc. do often have DC power options because that is a common use case. They typically though use mobile processors and are trying to compromise to be low power, low heat and increased battery life if applicable.

 

 

[akio123008]

8 hours ago, mariushm said:

No, 12v0 power supplies output only 12v

I think he means the input on the mobo. He's happy he then doesn't need converters to produce 5V, 3.3 etc.

 

However:

13 hours ago, treefroggy said:

I don't need a converter at all, since 12v is the power supply I'm already working with

I don't think that's a good idea. You see computer components do have some tolerance, but the range on a 12V battery system is quite big. You turn on a heavy load and it might be all the way down to 10.5, or your solar panel kicks in and it might go all the way up to 14.

 

The ATX spec doesn't allow for such big fluctuations (I think the official allowed range is 11.5 to 12.5 or something? idk, someone who's more into computer parts will know). That isn't to say that 14V will destroy your parts, because in many cases it'll be fine, but it does mean that it's not guaranteed to work properly.

 

Therefore even though the power source is "12V" good practice would be to still put (however silly it might sound) a 12V DC converter in between to make sure the output remains at a steady 12V.

[treefroggy]

6 hours ago, akio123008 said:

I think he means the input on the mobo. He's happy he then doesn't need converters to produce 5V, 3.3 etc.

 

However:

I don't think that's a good idea. You see computer components do have some tolerance, but the range on a 12V battery system is quite big. You turn on a heavy load and it might be all the way down to 10.5, or your solar panel kicks in and it might go all the way up to 14.

 

The ATX spec doesn't allow for such big fluctuations (I think the official allowed range is 11.5 to 12.5 or something? idk, someone who's more into computer parts will know). That isn't to say that 14V will destroy your parts, because in many cases it'll be fine, but it does mean that it's not guaranteed to work properly.

 

Therefore even though the power source is "12V" good practice would be to still put (however silly it might sound) a 12V DC converter in between to make sure the output remains at a steady 12V.

You are correct. I'm already highly aware of this. I monitor the voltage of my battery 20 times a day. The voltage of my system varies, of course. Using the voltage unconditioned is only safe for lights, audio amp, etc., and even then, not ideal. That's why the step up converter for 19v is so amazing and consistent for my pc and monitor! I use a 12v regulator to give a consistent 12v for my other devices.

 

7 hours ago, artuc said:

They're explaining why it's not really available because it's a niche that's not done by most people.

 

Cabling cost isn't such a big deal for something small like a vehicle where you may need a few metres at most. As you scale up you see more and more issues with the large current and therefore even 24 and 48VDC used if for some reason DC is preferred/needed.

 

The assumption is most built desktop PCs will be in a house and the house will have mains AC, because that is the reality for 99.9% of use cases.

 

Laptops, NUCs and PCs specifically for industrial, AV, displays/POS, surveillance/security etc. do often have DC power options because that is a common use case. They typically though use mobile processors and are trying to compromise to be low power, low heat and increased battery life if applicable.

 

 

Yeah, you are all stating the obvious facts I already know, and is irrelevant to my situation, which, I stated already is unconventional. Much of my electrical utilities are designed for use in boats. I'm basically building a gaming PC for a boat. It just doesn't help to say "here's why what you're doing is unconventional". That's just annoying. I already know what the standard is, I've gotten this far with my own problem solving. 

[treefroggy]

15 hours ago, mariushm said:

No, 12v0 power supplies output only 12v ... the 10 pin connector that replaces the 24 pin connector has power_ok , power_on , 12v stand by , 12v x 2 , ground ...

 

So it would be easier to make something or buy something that accepts some dc voltage and produces that 12v and the power_ok and power_on signals the motherboard expects (a 5-10 cent microcontroller can do those)

 

It could be as simple as an adapter cable that has a barrel jack at one end and the 10 pin and 8 pin cpu connector at the other end.

 

Yeah, I'll admit I don't understand this. Sounds like it's not as simple as just giving the correct voltage to each component.

[akio123008]

29 minutes ago, treefroggy said:

Yeah, you are all stating the obvious facts I already know, and is irrelevant to my situation, which, I stated already is unconventional

You seemed slightly annoyed with them for explaining that, but you have to realise, people post stuff like this all the time (where they have some unconventional thing in mind) and 90% of the time, they have no clue. There's no way people can somehow see your experience with the equipment.

 

27 minutes ago, treefroggy said:

Yeah, I'll admit I don't understand this.

What that is in a nutshell is: 

- you need the right cable to do it

- you probably need to mess around a bit with some control signals (like the signal to turn the power on/off etc.)

[Guest]

https://www.advantech.com/products/2d9aae24-dfb2-4741-bec5-62dca5bc9cd3/96ps-d500wps2/mod_1124e1ee-7c1d-4a84-930d-aea267015010

 

[melbaylon]

I'm in a very similar situation. I have an off-grid solar setup with 5kWh 12V battery bank. I want to build a relatively low power workstation PC for graphic design and a bit of 3D and motion graphics. I'm thinking Ryzen 5 3600 and a GTX 1650, up to a 1660 Super if power budget allows it. Been eyeing this 300W Pico PSU for the said project.

[mariushm]

7 minutes ago, melbaylon said:

I'm in a very similar situation. I have an off-grid solar setup with 5kWh 12V battery bank. I want to build a relatively low power workstation PC for graphic design and a bit of 3D and motion graphics. I'm thinking Ryzen 5 3600 and a GTX 1650, up to a 1660 Super if power budget allows it. Been eyeing this 300W Pico PSU for the said project.

Yeah, make sure that power supply actually regulates/filters the 12v output as well, because you don't want 13.5-14v from your battery bank going to your components. 

 

 

[melbaylon]

2 minutes ago, mariushm said:

Yeah, make sure that power supply actually regulates/filters the 12v output as well, because you don't want 13.5-14v from your battery bank going to your components. 

 

 

Yeah. I do plan to have a module between the battery and PSU to regulate the voltage.

[treefroggy]

What part would you ideally use for that? Just a voltage regulator transistor?

Also again, for everyone saying this isn't possible, soon there will be much higher demand for this as more crypto farms switch to solar energy. We're just slightly ahead of the curve here.

That picopsu you linked is awesome, and it's intended for miners lol. Thanks for linking it, that's exactly what I was looking for! I should just be looking at stuff targeted at crypto miners, similarly to how most of my van setup is stuff intended for boats.

Recently jays2cents made a video showing how to add an external gpu to the type of mini pc that I got since it has direct DC input, the adapter cable was intended for cryptominers as well.

 

 

On 7/16/2021 at 1:09 AM, melbaylon said:

Yeah. I do plan to have a module between the battery and PSU to regulate the voltage.

 

[Just that Mario]

First half the original post I thought OP was talking about laptops. By last bit I realised he means a desktop PC. Why do ATX power supplies exist? Well... because they're standardazied and supply constant and very specific voltage at upto specific current and they're easy to use and do what they're supposed to do fairly efficiently and well?

As for reading some of the other comments discussing voltage drops and 12V "not having great voltage drop" is just cringe. You need some seriously thicc cables to not have significant voltage drop at 12V over greater distances.

[treefroggy]

On 7/22/2021 at 2:26 PM, Just that Mario said:

First half the original post I thought OP was talking about laptops. By last bit I realised he means a desktop PC. Why do ATX power supplies exist? Well... because they're standardazied and supply constant and very specific voltage at upto specific current and they're easy to use and do what they're supposed to do fairly efficiently and well?

As for reading some of the other comments discussing voltage drops and 12V "not having great voltage drop" is just cringe. You need some seriously thicc cables to not have significant voltage drop at 12V over greater distances.

What is truly cringe:

Everyone in here warning--no-- threatening that it is impossible due to voltage drops: This is an exact science. The formula for voltage drop is elementary level electrical engineering. The reason voltage drop is not an issue for me is because I know the exact length and gauge wire that I will be using. I'm not going across a building, my power supply is three feet away from the PC. Everyone needs to calm down about DC voltage drop. The van is only 12 feet long end to end. I can get 13v anywhere inside the van.

 

It should be abundantly clear from the OP that I am not just talking about laptops, mini prebuilts, desktops. Laptops are a thing, that is the precedent for it being totally reasonable to run my desktop off direct DC.

[treefroggy]

It's not fricking rocket science. I already built the 12v system, so I think I know what I'm doing when it comes to wire gauging, lol. I've all kinds of devices-- including laptops, prebuilt mini pc, monitors, audio amp, usb charger, vacuum cleaner, water boiler, gameboy, air compressor etc off of DC.

I think I might just be on the wrong forum for this kind of discussion. Thanks for your help everyone, hope you have a good rest of your day.

[artuc]

On 7/23/2021 at 4:03 AM, treefroggy said:

What part would you ideally use for that? Just a voltage regulator transistor?

Also again, for everyone saying this isn't possible, soon there will be much higher demand for this as more crypto farms switch to solar energy. We're just slightly ahead of the curve here.

 

It's very possible, just if it is uncommon or niche you may not find it a easily or off the shelf. I needed a rather unusual power supply and could find nothing off the shelf. If it was for personal use I could have fairly easily put together a rectifier and then use a DC-DC module.

 

I personally think a lot of large scale solar could still be grid tied where possible and running mains inverters.

 

Anyway I feel like you possibly could make something up, but even now there are some issues, most of the pico psu and similar are fairly low power. 

 

A possibility higher power than a pico with off the shelf parts is a fairly hefty regulated buck-boost DC-DC for 12VDC, ideally with a remote off terminal, then 3.3V and 5V DC-DC fed from that. For the 5V standby a small low current wide input module always powered, then hack up ATX power leads

 

Might be missing something but may be vaguely doable.

 

An inverter is the easy option.

5 hours ago, treefroggy said:

I think I might just be on the wrong forum for this kind of discussion. Thanks for your help everyone, hope you have a good rest of your day.

 

The knowledge is here but while what you're after isn't entirely unreasonable it just doesn't really exist.

 

Personally I'd use an inverter in your situation as I would prefer parts that can work on mains and are easily replaceable and I have little tolerance for stuffing around looking for solutions these days.

[treefroggy]

Here's some pics of my setup.

Battery currently at 13.5 volts. A 6 foot cable, at the other end, still 13.5 volts. The gauge is probably thicker than needs to be.

Big silver brick is the 19v step up converter. For efficiency, I would run a desktop PC like this. From what I understand, I'd just need a converter for each voltage input. Seems doable.