2x DC-DC PSU Possible?

[michaelmitchell]

Has anyone used 2x DC-DC PSU's like PicoPSU or HDPLEX for powering a SFF build? For example... one to power the Motherboard, CPU and SSD's and the other for dedicated PCI-E power?

Would there be any obvious problems in doing so?

If using a flexible PCI-E riser and a GPU with additional power connectors will the GPU draw power from the motherboard as well?

 

[confusis]

I believe @Tek Everything was working on the idea.

 

[Ceros_X]

There are a few dual brick systems that I have seen, I think the ASUS ROG G20 is one of them.

The PCI-E slot is speced to provide 75W of power (Thin mITX PCI-E 4x slots only provide 25W). I have seen a few people suggest cutting the trace that provides power to the PCI-E slot if you plan on using a second board to provide power.

What card are you planning on running that can be powered by an HD-Plex with a 330W brick? The HD-Plex can run much higher than the 250W it is rated for..

 

[jØrd]

not sure if this would work on a picoPSU / HDplex but its a nice compact solution
http://www.add2psu.com/

 

[Tek Everything]

@michaelmitchell I actually just did this last week. I just made a quick thread about it.

Simple Dual Pico PSU Set Up

 

[michaelmitchell]

@michaelmitchell I actually just did this last week. I just made a quick thread about it.

Simple Dual Pico PSU Set Up

Thanks Tek, that is exactly what I wanted to see, I have been in the same situation as you regarding the HDPLEX so I've been considering alternatives and dual Pico style came to mind as a good if not better alternative, I am actually going to test Pico Box Z3-ATX-200 which have a peak of 240w and I imagine like the PicoPSU can be pushed further than rated if kept cool so I will stick some heat sinks on there and make sure they get some airflow.

There are a few dual brick systems that I have seen, I think the ASUS ROG G20 is one of them.

The PCI-E slot is speced to provide 75W of power (Thin mITX PCI-E 4x slots only provide 25W). I have seen a few people suggest cutting the trace that provides power to the PCI-E slot if you plan on using a second board to provide power.

What card are you planning on running that can be powered by an HD-Plex with a 330W brick? The HD-Plex can run much higher than the 250W it is rated for..

Other than the HDPLEX still being out of stock even though the expected stock date was today/yesterday the reason I am exploring dual PSU is that currently the Dell PA-9E 240w power adapter provides the most power for its volume and weight, in fact it is close to half the weight & volume of the 330W so for roughly the same or a little more volume and weight I could run dual Dell 240w totalling 480w giving me loads of extra power to work with for high performance builds.

What I am currently wondering is if the PCI-E slot will provide power to the GPU and will it provide power first or secondary to the power connectors on the card, I have heard the same things about "cutting the power to the PCI-E slot" but it has never been backed up by anything but guesswork so may be completely unnecessary and perhaps outright stupid.

 

[QinX]

Cutting PCIe power is not guess work.

Tom's Hardware does very in depth power consumption testing with osciloscopes and it differs from GPU to GPU. Some draw almost nothing, some draw a lot.

One thing is certain, every GPU needs to have 12V applied via the PCIe slots. Be it via a Molex connector of via the PCIe slot itself. I'm not sure if this is PCIe Spec related or a way to guarantee proper booting of the system.

I tried booting a 970 and a Nano without 12V via the PCIe slot and it was a no-go.

Some info from their reviews of the 970 980 and 980 Ti
Motherboard 12 V
980: 34.98 W
970: 42.84 W
980Ti: 47.17W

http://www.tomshardware.com/reviews/nvidia-geforce-gtx-980-970-maxwell,3941-12.html
http://www.tomshardware.com/reviews/nvidia-geforce-gtx-980-ti,4164-7.html

 

[Tek Everything]

Thanks Tek, that is exactly what I wanted to see, I have been in the same situation as you regarding the HDPLEX so I've been considering alternatives and dual Pico style came to mind as a good if not better alternative, I am actually going to test Pico Box Z3-ATX-200 which have a peak of 240w and I imagine like the PicoPSU can be pushed further than rated if kept cool so I will stick some heat sinks on there and make sure they get some airflow.

Other than the HDPLEX still being out of stock even though the expected stock date was today/yesterday the reason I am exploring dual PSU is that currently the Dell PA-9E 240w power adapter provides the most power for its volume and weight, in fact it is close to half the weight & volume of the 330W so for roughly the same or a little more volume and weight I could run dual Dell 240w totalling 480w giving me loads of extra power to work with for high performance builds.

What I am currently wondering is if the PCI-E slot will provide power to the GPU and will it provide power first or secondary to the power connectors on the card, I have heard the same things about "cutting the power to the PCI-E slot" but it has never been backed up by anything but guesswork so may be completely unnecessary and perhaps outright stupid.

Nice, I haven't tried any of the Pico Box products yet. It is a little concerning that all that power will be traveling over one peripheral cable. Let us know how it turns out.

 

[michaelmitchell]

Cutting PCIe power is not guess work.

Tom's Hardware does very in depth power consumption testing with osciloscopes and it differs from GPU to GPU. Some draw almost nothing, some draw a lot.

One thing is certain, every GPU needs to have 12V applied via the PCIe slots. Be it via a Molex connector of via the PCIe slot itself. I'm not sure if this is PCIe Spec related or a way to guarantee proper booting of the system.

I tried booting a 970 and a Nano without 12V via the PCIe slot and it was a no-go.

Some info from their reviews of the 970 980 and 980 Ti
Motherboard 12 V
980: 34.98 W
970: 42.84 W
980Ti: 47.17W

http://www.tomshardware.com/reviews/nvidia-geforce-gtx-980-970-maxwell,3941-12.html
http://www.tomshardware.com/reviews/nvidia-geforce-gtx-980-ti,4164-7.html

Just to be clear and make sure I am understanding you correctly, you are saying that "cutting the trace that provides power to the PCI-E slot if you plan on using a second board to provide power" is indeed not a very good suggestion as I suspected since the GPU must draw from the PCI-E slot?

Do the riser cables like the one for the S4 mini carry the power ok or is a powered riser required? My assumption has been that they must since I've seen GTX750TI running just fine on them.

So from my very limited thinking and knowledge... very limited.... with a dedicated 240w power brick for the GPU my supply to the GPU would actually be higher than 240w with some power coming through the PCI-E slot which should give me enough wiggle room to run most if not all cards.

Nice, I haven't tried any of the Pico Box products yet. It is a little concerning that all that power will be travelling over one peripheral cable. Let us know how it turns out.

I found them while looking around for alternatives and figured it would be worth a try, if only to report back here to see what I find. I have heard they run rather hot so I have some small heat sinks queued on the same order once I decide to pull the trigger, they seem to use higher gauge wires than PicoPSU but I am prepared to replace all the cables if needed and for the second PSU I plan to only have a single PCI-E connector wired to it.

 

[QinX]

Just to be clear and make sure I am understanding you correctly, you are saying that "cutting the trace that provides power to the PCI-E slot if you plan on using a second board to provide power" is indeed not a very good suggestion as I suspected since the GPU must draw from the PCI-E slot?

Do the riser cables like the one for the S4 mini carry the power ok or is a powered riser required? My assumption has been that they must since I've seen GTX750TI running just fine on them.

So from my very limited thinking and knowledge... very limited.... with a dedicated 240w power brick for the GPU my supply to the GPU would actually be higher than 240w with some power coming through the PCI-E slot which should give me enough wiggle room to run most if not all cards.

You are correct.
the GPU MUST have a 12V supplied via the PCIe slot, either directly via the PCIe slot itself, such as the S4 Mini. Or via a seperate connector. Such as a powered riser cable.

If you have a lot of leeway in your power budget you can just power the GPU partly via the motherboard and partly via the PCIe PEG connectors. However if you are on a tight powerbudget and need to have more control/certainty you will want to cut the 12V that enters via the motherboard and use/make a powered riser.

One thing that I can't say for certain is what happens if the GPU wants 60W of power via the PCIe slot and the motherboard can only supply say 30W. will the GPU automatically draw 30W lesson the PCIe slot and take 30W extra via the PEG connectors or will it result in a black screen because the GPU had a big voltage drop.

 

[michaelmitchell]

Fantastic, it is actually perfect in my case since I will be running an over powered brick for the motherboard so taking even the max of 75w would be no problem. I would be really interested to test the R9 Nano using this setup to see if it were any better off having its own dedicated power source rather than sharing with the motherboard.