[SOLVED] Server PSU for multiple mobos

[melco]

Hi
I want to build a 4-mobo custom box with a new Ryzen 9 5950x when available. The idea is to have one server PSU. Something like 80Plus Platinum 2000W+. Server PSU has only a 12V line and at the same time, it is the only voltage that has the most consumption nowadays. There are two ways I think to power it all today:

1. normal low-power ATX PSU with 24pin y splitters + server PSU for powering CPU 4+4 lines and GPUs on all mobos
2. Server PSU powering GPUs and CPU 4+4 lines and four Pico PSUs powering mobos.

My understanding that minimal 120W pico PSUs should be enough having CPU powered by server PSU.
Questions:

1. Will that work or there are any obvious problems?
2. Should I connect 12v GND with the GND of Picos or ATX PSU? So that +12V has a common GND.

P.S. Please don't post off-topic questions regarding the use case or why don't I just buy 4 ATX PSUs

 

[mossberg]

Seems like a lot of cost, time and effort. Just get a Threadripper 3990x, or wait for 4th gen Threadripper.

 

[Rogue Leader]

I want to build 4-mobo custom box with new Ryzen 9 5950x when available.

Interested to know why? Like whats the application for this setup

 

[melco]

Threadripper is an option but:

1. I'm not sure it can easily be overclocked even to frequencies normal for R9 3950x overclocking. Not even talking about close-to-5GHz clocks for R9 5950
2. Zen-3 threadripper won't be around for another year I suspect while R9 5000 series will be readily available even in 2020

 

[melco]

Interested to know why? Like whats the application for this setup

Hmm. many computers with powerful CPUs. What could it be? Maybe a compute cluster? Rendering farm? Machine learning farm?

 

[USAFRet]

Hmm. many computers with powerful CPUs. What could it be? Maybe a compute cluster? Rendering farm? Machine learning farm?

Multiple systems is one thing.
Multiple systems running from one PSUs is quite another.

 

[melco]

Yeah. The topic is really about multiple systems and one PSU (Pico PSU is not an independent unit in that regard and requires 12V)

 

[logainofhades]

You can do 2 systems, in a single case, easily enough, with some of Phanteks's offerings. 4 is a stretch.

 

[Rogue Leader]

Hmm. many computers with powerful CPUs. What could it be? Maybe a compute cluster? Rendering farm? Machine learning farm?

Yes, thats exactly what I'm asking, what are you doing with it and why so cagey? Just interested to know.

And I agree with USAFRET I wouldn't use one PSU to power it, while you'd probably have a good quality unit, its one big failure point that can take you all the way down in the event of a failure.

 

[melco]

You can do 2 systems, in a single case, easily enough, with some of Phanteks's offerings. 4 is a stretch.

Nono, it will be a custom case with immersion phase-change cooling and the PSU will be potted with epoxy resin. But that's a whole another story.

 

[USAFRet]

...and the PSU will be potted with epoxy resin.

Thereby removing any air flow the PSU will need.

 

[melco]

Yes, thats exactly what I'm asking, what are you doing with it and why so cagey? Just interested to know.

And I agree with USAFRET I wouldn't use one PSU to power it, while you'd probably have a good quality unit, its one big failure point that can take you all the way down in the event of a failure.

Well. It will be a compute cluster. The task is CPU-heavy and scales well on multiple CPU cores. Server PSUs are rather reliable so it's not an issue in my case.
I want to know only few things:
is it possible/safe to power CPU (EPS 4+4) directly from 12V of server PSU? Should I make a common GND between ATX psu (be it pico or normal PSU) in that case?

 

[melco]

Thereby removing any air flow the PSU will need.

yes, immersion cooling will take care of removing the heat. Offtopic here

 

[melco]

Guys posting here. The setup is far from common and many aspects of it are still to be figured out. But in this topic, there is a narrow scope of questions. Let's talk specifically about powering multiple mobos with one PSU as outlined in the initial post. Thanks

 

[USAFRet]

Mainly, we're wondering about the requirement for a single PSU?

4x systems and 4x power supplies. No problem.
All in a custom immersion tank. Go for it.

 

[Zerk2012]

I would agree why try to rig something up.

4 PC's in a custom made case and run one power switch to every board so push one button and they all cut on.

 

[Rogue Leader]

Well. It will be a compute cluster. The task is CPU-heavy and scales well on multiple CPU cores. Server PSUs are rather reliable so it's not an issue in my case.
I want to know only few things:
is it possible/safe to power CPU (EPS 4+4) directly from 12V of server PSU? Should I make a common GND between ATX psu (be it pico or normal PSU) in that case?

Got it, cool.

Now back to your problem. I still do not like it. Mainly because Server PSUs do not have 24 pin outputs, they are all proprietary to their boards (of which there are only a handful of manufacturers). So you're going to need to cut the connector off of the PSU and wire it up, and split it up properly. You're talking about 166 amps out, that you need to properly split to 4 board connectors. Without all the proper connections since a lot of the voltage regulation of a server PSU to the hardware on the motherboard is done on the board side. IMO thats a recipe for blowing something up.

 

[melco]

Got it, cool.

Now back to your problem. I still do not like it. Mainly because Server PSUs do not have 24 pin outputs, they are all proprietary to their boards (of which there are only a handful of manufacturers). So you're going to need to cut the connector off of the PSU and wire it up, and split it up properly. You're talking about 166 amps out, that you need to properly split to 4 board connectors. Without all the proper connections since a lot of the voltage regulation of a server PSU to the hardware on the motherboard is done on the board side. IMO thats a recipe for blowing something up.

Oh really? I know only that server PSU is a plain source of 12V. Miners use it for GPU powering just fine. They never mess with proprietary connectors or any regulation you are talking about. Did you ever work with server PSUs? What can be blown you think and why? I mean you sure about what can go wrong because you know or you just afraid because you DON'T know?

 

[USAFRet]

Yes, many/most server power supplies are proprietary to the associated motherboard.
Unlike regular ATX spec, they are not mix and match.

What can go wrong?
Getting one single wire connected to the wrong place, or a substandard connection, or simply trying to suck too much amperage through a wire gauge not designed for that.

 

[melco]

I would agree why try to rig something up.

4 PC's in a custom made case and run one power switch to every board so push one button and they all cut on.

I can get server 80Plus Platinum PSU for something like 50USD and 4 picos for like 50USD. some 20usd for cables. 120USD all in all.
That's cheaper than a single 80Plus platinum ATX PSU. And no, I don't think 4 consumer-level PSUs would be more reliable than the server PSU.

 

[melco]

Yes, many/most server power supplies are proprietary to the associated motherboard.
Unlike regular ATX spec, they are not mix and match.

What can go wrong?
Getting one single wire connected to the wrong place, or a substandard connection, or simply trying to suck too much amperage through a wire gauge not designed for that.

https://www.google.com/search?q=IBM+psu+mining
So damn common that I don't think we should even discuss that. They are just plain regulated 12V power supply with some additional functionality I don't need but I don't care much. It's a reliable source of 12V and that's what I need from it the most. 5V and 3.3v can be provided from a Pico or low power ATX psu, doesn't matter.
All in all: no, it's not uncommon. No, it's not hard to get 12V out of server PSU

Using wrong wire, wrong polarity, wrong gauge: not the case. I can be done right. The question was whether I need a common ground? Can I supply 12V from a different PSU to avoid overloading the Pico? Are 24pin Y splitters OK if ATX PSU is used to power mobos?

 

[USAFRet]

4x 5950x @$800 ea - $3200
4x unknown GPU - $1500(?)

Run from $120 PSU components.


Please...I implore you. Send us some pics and video of this thing running.

 

[melco]

120$ PSU is an 80Plus Platinum PSU. It's not some BS from China. And no, if you have a 5000$ rig doesn't mean your HDMI cable should cost 200$, right?

 

[USAFRet]

120$ PSU is an 80Plus Platinum PSU. It's not some BS from China. And no, if you have a 5000$ rig doesn't mean your HDMI cable should cost 200$, right?

2 completely different things.

 

[Rogue Leader]

Oh really? I know only that server PSU is a plain source of 12V. Miners use it for GPU powering just fine. They never mess with proprietary connectors or any regulation you are talking about. Did you ever work with server PSUs? What can be blown you think and why? I mean you sure about what can go wrong because you know or you just afraid because you DON'T know?

I don't appreciate the implication that I don't know what I'm talking about, I've been working with Computers and building systems from Servers to game machines for the better part of 30 years.

GPUs only need power and ground specifically (everything else is provided via the PCIe slot), modifying a connector (or using an adapter) to provide that to a bunch of GPUs is no big deal.

THIS is the pinout of a 24 pin connector:

https://www.lifewire.com/atx-24-pin-12v-power-supply-pinout-2624578

No 2000w Server PSU from any reputable manufacturer that I have seen has a 24 pin on it, because server motherboards do the breakdown you see in that connector, so unless you find a way to not feed 166amps into the motherboard connectors which can't handle that, what can happen? You burn the connector, or you fry the chipset, or worst case you fry the CPU (unlikely though). Theres a reason the 24 pin is broken down like that, because different parts of the connector go to different parts of the board, and you don't want to exceed the power capacity of the wiring.

Now, Is there a way to do this? Well yes there sure is, but its complicated, and from your line of questioning beyond your level of electronics expertise. You're not doing it with adapters, you are going to need to bust our the soldiering iron, some capacitors, resistors, etc. Its one of those if you have to ask you probably shouldn't be doing it type of deals.

I can get server 80Plus Platinum PSU for something like 50USD and 4 picos for like 50USD. some 20usd for cables. 120USD all in all.
That's cheaper than a single 80Plus platinum ATX PSU. And no, I don't think 4 consumer-level PSUs would be more reliable than the server PSU.

If you're paying $50 for them they are used, there is no way you're buying new ones for that price unless they are stolen, or cheap junk. They are between $300 and $400.

If you're finding ones with 24 pin connectors on them, then they aren't quality units. I don't care about the Platinum rating, that is efficiency only and has no bearing on quality.