Build Separate GPU Enclosure - Will this work?

[dom99]

Hi,

I've been thinking about whether this would work and would like some input from others.

I've got a tiny Mini-ITX PC I built with Kaveri 7850k in a streacom f1c evo WS (modded the top take a 120mm fan intake for extra cooling) running off a Pico PSU with 150W of power available and I'm pleased with the results, have had this setup for a year now.

However my AMD R9 290 GPU has become a little unused and I think this is because its sitting in a PC I don't really use ATM.

What I want to do is put together a box with PCI-e extender cable, a separate PSU (Silverstone SFX 450W Gold) and GPU which can be attached or removed when required.

My only question really is the GPU power requirements and how it will load on the already maxed out 150W Pico PSU.

Will the GPU still draw 75W from the motherboard even when connected via its own power supply?

Thanks
Dominic

 

[dom99]

Here is an image of the mini pc with top lid mod, although I later swapped the case for a version without the OD gap.

 

[CAPSLOCKSTUCK]

Great project, hope you keep us updated.

I cant answer your question but someone will soon i expect.

I have used 2 psus in a system before, cables bloody everywhere.

 

[xvi]

Some PCIe extenders (the ones that use a USB cable of some sort, iirc) have a separate molex connector. I would suspect the 75w would be drawn off that, but I wouldn't know for sure. Those extenders are popular for Crypto mining rigs that utilize many GPUs, so I think it's safe to say yes. The downside is those extenders usually run PCI-e 1x, not 16x. You might be able to find a PCI-e riser and just chop the wires feeding 12v and 3.3v and splice in something direct from the PSU.

Edit: Might be able to go in to the BIOS and set the PCIe slot wattage down to something minimal though. Could be easier than chopping up risers.
Actually, come to think of it, if you're using a dedicated GPU, wouldn't that deactivate the integrated GPU and free up some precious watts?

 

[dom99]

Some PCIe extenders (the ones that use a USB cable of some sort, iirc) have a separate molex connector. I would suspect the 75w would be drawn off that, but I wouldn't know for sure. Those extenders are popular for Crypto mining rigs that utilize many GPUs, so I think it's safe to say yes. The downside is those extenders usually run PCI-e 1x, not 16x. You might be able to find a PCI-e riser and just chop the wires feeding 12v and 3.3v and splice in something direct from the PSU.

Edit: Might be able to go in to the BIOS and set the PCIe slot wattage down to something minimal though. Could be easier than chopping up risers.
Actually, come to think of it, if you're using a dedicated GPU, wouldn't that deactivate the integrated GPU and free up some precious watts?

Thanks for the info and ideas, I will certainly research the PCI-e risers which have USB connections.

With regards to the disabling of the integrated GPU I would rather not as it is not a guarantee that it will use less Wattage and also creates more problems when swapping the dedicated GPU in and out.

 

[Caring1]

If you don't use the optical drive bay slot, bring the riser to that point and fix it internally, then the card can be slotted in from outside the case, an external power source will still be needed for the 6 and 8 pin plugs on the card.
It should work in theory.

 

[dom99]

Y

If you don't use the optical drive bay slot, bring the riser to that point and fix it internally, then the card can be slotted in from outside the case, an external power source will still be needed for the 6 and 8 pin plugs on the card.
It should work in theory.

Yes could do that but the aesthetics are a concern with anything coming out the front, I will probably use a space in the back with a small grill, remove it and screw on a hinged flap.

 

[dom99]

To this I am using the modular Silverstone SFX PSU (in picture) and the R( 290 GPU attached to the riser PCB used in the Silverstone ML07 to go inside the box.

In addition I bought a molex powered riser and also a dual PSU adapter which should arrive early next week.

I will attach a proof of concept photo when I have it set up. If it works then I will go about building a box for the GPU and PSU to live inside.

 

[Brusfantomet]

Only advice i can come with is to make sure the 0V from both PSUs is connected together, otherwise you could kill some parts of the MB and/or GPU

 

[Caring1]

Only advice i can come with is to make sure the 0V from both PSUs is connected together, otherwise you could kill some parts of the MB and/or GPU

Another option is to remove the Pico 150W from service, and just use the external supply to power the system and card.

 

[dom99]

Only advice i can come with is to make sure the 0V from both PSUs is connected together, otherwise you could kill some parts of the MB and/or GPU

Thanks for the advice but could you please elaborate on why this would happen, where the 0V connection on the PSU is (I assume it is one of the 24 pins) and how to do it (would it not be connected via the dual PSU adapter already?)

I would post a link to the adapter I bought but ebay is blocked on my work PC

 

[dom99]

Another option is to remove the Pico 150W from service, and just use the external supply to power the system and card.

I wouldn't want to do this because I want to be able to just have the case as a stand alone PC when I'm moving around, so it needs to work without the GPU and extra power supply connected.

I want to do this for a combination of factors really:
1. I like SFF PCs, they take up less space, look better and are easily portable
2. I like high end graphics when gaming
3. I want the convenience of separating points 1 and 2 to have the best of both worlds, the smallest SFF case possible when I don't want or need the extra graphics performance, and when I do need the performance not having to rebuild the whole PC into another case (as I have been doing with the Silverstone ML07 and the streacom F1C Evo, constantly seem to be swapping them around)

4. I just want to see if I can just for the hell of it

 

[R-T-B]

I have some old PCIe x16 > x16 risers from my GPU mining days if you need any. I'm not sure what condition they are in though.

They used to make some kind of part in the bitcoin mining scene that did exactly this... let you power the same system with more than one PSU. Unfortunately, I have no fricking clue what it's called and I remember it being a bulky piece of PCB... so probably not very useful.

However be aware, if you just start plugging more than one PSU into the same system without doing things properly, it has been known to do terrible, terrible things. Electrical fire type stuff... or so the stories went.

 

[NC37]

I have an old Thermaltake 5.25 GPU PSU. Still works. It uses a cable adapter to enable dual PSUs in 1 system. You plug the regular PSU into the adapter. Although all the power goes through 6 pin connectors as the GPU PSU has it's own power cord. So literally I just think the adapter is only there to register when the PC turns on.

Dunno if that gives an idea but the adapters do exist.

 

[Brusfantomet]

Thanks for the advice but could you please elaborate on why this would happen, where the 0V connection on the PSU is (I assume it is one of the 24 pins) and how to do it (would it not be connected via the dual PSU adapter already?)

I would post a link to the adapter I bought but ebay is blocked on my work PC

just connect one 0V from the SFX to one on the Pico, its the black ones on PCUs with colored cabels, but seeing as ALL the cables from the SFX is black i would use a spare molex, the two center ones are 0V example, if you want to use the 24 pin, here is a example of the wiering in those.



Note that if the dual PSU adapter connects teh two 0V's together fidelign with the mlexes is not nesecery, if you could get a picture it would be easy to determine if it does that.

The danger of having unmatched 0V planes is that a PSU generates the voltage difference between the 0V plane and the rail, so if the pico PSU 0V plane is 10 V lower than that of the SFX PSU your signaling form the GFX card to the MB would be 11V to 14V in stead of 1V to 4V, that would damage the MB. Normaly its not cuch a big problem because the PSUs use ground in the sockets to hold the 0V correctly, but depending on how your Pico PSU is powered it can have a floating 0V witch is bad news.

However be aware, if you just start plugging more than one PSU into the same system without doing things properly, it has been known to do terrible, terrible things. Electrical fire type stuff... or so the stories went.

Floating 0V can cause that, or using two PSUs to power the same GPU, as one PSU may give 12,1 V and another gives 11,9 V, that 0,2 V difference is nut much, but if the GPU conets all the 12V inputs to the same spot its going to have very low resistance, in the mOhm area, lets say 5 mOhm, that gives a extra pull of 0,2V/0,005 ohm = 40A, enough to damage many PSUs, especially the one getting 40 A in revere on the 12V rail.

 

[dorsetknob]

Will the GPU still draw 75W from the motherboard even when connected via its own power supply?

Short answer is Yes Modern cards draw up to 75w from the slot and the extra power they require from the Pcix 12v Plug in cable (s)

Long Answer ask @Wizzard

 

[Brusfantomet]

You could splice the 12V feed from the SFX PSU into the 12V on the riser, but that would reqier you to split the ribbon cable at the 4 wires that give 12V and solder on a connector for the SFX supply.

 

[dom99]

Here is the dual psu adapter I bought to connect the second psu

http://m.ebay.co.uk/itm/281318983561

Here is the powered PCI-e x16 extender

http://m.ebay.co.uk/itm/191113158263?txnId=1144419183009

What I am hoping is that by using the dual psu adapter it will turn the psu on at the same time as the rest of the system

Using the powered PCI-e riser I am hoping will prevent the GPU from drawing the potential 75W from the motherboard and pull all power from the second psu.

Can someone please tell me if this has the potential to be dangerous? As far as I'm aware it doesn't use two different power sources for any one component and so slight voltage differences shouldn't be a problem.

Correct me if I'm wrong.

Looking online there is an alternative to the dual psu adapter linked here called the Add2PSU. Does anyone know if this is any better than than what I am using?

 

[Brusfantomet]

The dual PSU adapter will turn the SFX PSU on when the system is turned on, it does that by shorting pin 16 to 0V (the black ones also named ground) to do what is caled a "jump start" of the PSU (handy for testing a water loop for leaks without starting you computer). Since it has two cabels (one for pin 16 and one for 0V) it will hold the 0V for both PSUs at the same level, so no fiddling around with the molexes as i mentioned earlier

Note that if the dual PSU adapter connects teh two 0V's together fidelign with the mlexes is not nesecery, if you could get a picture it would be easy to determine if it does that.

The riser also looks like it takes the PCI-E power from that molex, meaning that as long as you connect the SFX supply to the GFX card AND that molex you should not draw any power from the pico PSU, but it will also mean that you will have to remove the hole ricer card when you dont want to bring the extra GFX card with you.

In short: yeah, it will probably work with the parts you have gotten of ebay.

 

[OneMoar]

risers can be pretty dam finicky
PCI-e does not like long circuit paths it may refuse to work or only operate in x4 or 8x mode
also you need to make both psu's turn on at as close to the same time as possible it needs to be <25MS from the time psu0 turns on to the time psu1 turns on else the system may not post
and I would not split the psu load both the molex on the peg extender and the pci-e power connectors should be connected to the same psu(unless you really know what you are doing)
and the powered adapter is not bi-directional if you look closely the power pins are not connected on the motherboard side of the extender

 

[dom99]

Ok all the parts have arrived, I plugged it all in but by bit.

Plugged the dual PSU adapter in, both PSUs start up fine.

Plugged in the PCI-e adapter with moped connection to other PSU. The PC turns on and works fine.

Attached R9 290 GPU and turn PC on, we get problems. The second PSU starts up and so does the GPU. 5 seconds later both the second PSU and the GPU power down and then automatically start up again. This cycle just continues until I turn the PC off. I have a power meter and the second PSU doesn't register more than 22 Watts. I have checked all connections and it seems right to me.

Has anyone got any advice? The PC still works fine when the GPU is disconnected again. I'm not quite sure why this is happening though

 

[CAPSLOCKSTUCK]

I would try without the adapter, fire up the extra psu by hotwiring before you start the pc and do the reverse on shut down , so pc off then 2nd psu off.

That worked when i did it.

 

[dom99]

I would try without the adapter, fire up the extra psu by hotwiring before you start the pc and do the reverse on shut down , so pc off then 2nd psu off.

That worked when i did it.

Hm but that was the whole point of the adapter that I wouldn't need to do that, also the fact that the PSU turns on in the first place means the connection must be ok, it just seems to not be able to draw enough power

 

[dorsetknob]

There is probably to much Time lag( only mili seconds ) between the main PSU powering up the Motherboard and the secondary Psu Powering up your external graphics card
those miliseconds count as the motherboard does not register your external card via the riser extention so when the 2nd PSU kicks in Your Bios allready assumes that there is only the other graphics system.
To Overcome this your external card needs to be powered before the main psu is switched on
@CAPSLOCKSTUCK has the right idea

fire up the extra psu by hotwiring before you start the pc and do the reverse on shut down , so pc off then 2nd psu off.

That will allow the card to signal to the bios that it is installed at BOOT UP

 

[dom99]

There is probably to much Time lag( only mili seconds ) between the main PSU powering up the Motherboard and the secondary Psu Powering up your external graphics card
those miliseconds count as the motherboard does not register your external card via the riser extention so when the 2nd PSU kicks in Your Bios allready assumes that there is only the other graphics system.
To Overcome this your external card needs to be powered before the main psu is switched on
@CAPSLOCKSTUCK has the right idea


That will allow the card to signal to the bios that it is installed at BOOT UP

Ok I will try this tomorrow cheers both of you