Possible to switch between desktop GPUs? (HD 5670 for normal, 2x HD 5850 for gaming)

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moley1390

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Mar 13, 2013
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Hi all, this is my first post on Tom's Hardware (although I've been reading for a long time now)

Here's my situation. I have set up a near-silent PC for recording. It has a 400W fanless PSU, and I've got it running nicely with a Gigabyte HD 5670 card.

I've just inherited 2x Asus HD 5850 cards which I hope to run in crossfire for gaming. I've got a 680W (noisy) PSU hanging around which I'm going to use just to power the HD 5850s (via the 6 pin plug).

My motherboard is a Gigabyte X58A-UD3R, and I was planning to install the two 5850s on the first two PCIEx16 slots, and then install my existing 5670 on the third PCIE slot (which shares bandwidth with PCIE 1).

What I would like to do, is when I'm gaming, turn on my external supply (powering the 5850s), and use those in crossfire, and when I'm recording, switch off the external supply and use the 5670. My concern is that when I switch off the external supply, the 5850s will attemp to draw power from the motherboard connector, and overload my PSU (and possibly motherboard).

Is this assumption correct? Is there any smart way to set this up without having to physically swap the cards every time I want to change activities?

Thanks in advance - I know it's a tricky one!
 
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gcurchod

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Mar 19, 2013
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Hi,

Your assumption seem correct... at least, you don't really known what will be the comportment of the PCI-e.
Anyway, I'm pretty sure a PCI-e graphic card doesn't have hot-plug capabilities.
Hence, I think you'll need to restart your computer with both PSUs turned on to have your HD 5850 recognized.
Then you should turn off your PC and restart with the 400W PSUs only to come back to your "non-gaming" configuration.
However, I've serious doubts that the PC will agree to start with non-powered graphic cards installed...
Moreover, if your PCIEX8_1 (third PCI-e) is populated, (and since it is shared with PCIEX16_1 (first PCI-e)), the PCIEX16_1 will only operate up to x8 mode.
(cf. http://www.gigabyte.fr/products/product-page.aspx?pid=3305#sp)... which would not be good for your CrossFire.

For me, you should consider acquiring a new PSU... I have a very similar PC (GA-X58A-UD7, 2x HD5850) with a Seasonic X-750.

Hope this helps
G.C
 
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moley1390

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Mar 13, 2013
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10,510


Hi,

Thanks for your reply, I wasn't planning to hotplug, I was planning to change over during reboot. That's a good point you make with the slot 1/3, hadn't quite thought about that. I've got a PSU which is capable of running them, it is simply the noise issue I was trying to fix (the cards are super noisy as well, obviously!). I'm thinking at this stage it's looking like I'll just have to seriously re-model my machine every time I want to switch between the two configurations, until I can afford to have two different machines entirely.

For any other posters reading this thread, I am also still wondering (to minimise how much I have to change between set-ups) if the Unpowered cards left in the slots would attempt to draw power through the PCI-E slot (thus overloading either the slot or the smaller PSU)

Cheers,
Scott
 
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