I have always wondered which supply is tapped first on a video card - Does it draw the max 75w at the motherboard first, (or in this case, 25w) then supplement with any extra connectors connected directly to the videocard? Or vice versa? Or does it mediate between all the connections? I was brainstorming some video card ideas with the DQ77KB, and I can easily hook up a secondary power supply directly to the video card's 2 6-pin connectors if need be, which would supply all 150w the card needs at max TDP (running average is more 120~), and that max is fuhrmark incited. I wouldn't want to get a DQ77KB, hook up the videocard with it's seperate power supply, then have it draw 75w on the PCIe slot and fry something anyways.
We would not recommend installing an additional power supply on the system. In this case the PCI will provide 75W as maximum. If additional power is required for the graphics card, it will be provided by the power supply using its external power connector.
Even though the documentation makes mention of only 25W allowed through the PCIe x4 connection? Unless you're saying it can do the normal 75w, no problem. I plan to run one of the T- model ivy bridge chips as the CPU, nothing more than a 45w tdp, possibly turbo disabled if necessary. I have watt meters handy, and can keep an eye on current draw on all ports if necessary.
I can also isolate the 12v lines of the PCIe port with a riser cable/card, and redirect it, and the 2, 6 pin PEGs, to a completely seperate supply, with it's own on-switch. But that'd be a hassle I could avoid if the PCIe port can do 75w just fine anyways. I had read that all the power inputs on graphics cards are galvanically isolated, so I could use multiple power supplies if necessary.
I was reading the technical specifications on the DQ77KB, and noticed it has changed the max amps to 12, when it was formerly at 8 I believe. Is that 12 amps at 19v input? Or any input? What's the deal? Has there been revisions on the hardware they are sending out now, or has the specification changed just as more testing has been done?
Either way, thanks for the help and reply. Hope I can get a handle on this BEFORE I fry anything.
I'm running a Sapphire 7750 LP (TDP 55W) on my DQ77KB (with a i7-3770S) and it seems to work fine. I play Skyrim, Mass Effect 3, Crisis 2, etc on it and I don't have problems. Although if gaming was your primary purpose I would look into a different board with a x16 PCIe slot as well as a flex PSU (assuming you have an its case) that will supply 400W so you can use a better card than my 7750.
My next project will be involving this board, and it's PCIe slot, come hell or high water. I'll be able to post my results then, but it might be a month or two.
Occasionally I get the message 'your graphics driver has recovered from an error' or something like that (reported by amd catalyst). I'm starting to think that it may be the 25w power limitation that is the issue. Once I get my system up and running again, ill play around with power settings in amd overdrive and see what happens. I think any modern gpu is going to expect 75w from the slot, so I'd be hesitant to even try a power hungry card with a separate PSU.
I have been using this board with an HD7850 and an ATX PSU hooked up to power on when the board powers on.
No problems whatsoever apart from the fact its only running at 4x (I used a dremil to carefully remove the piece of plastic at the end of the slot that stops larger cards from fitting )
I also have a 30GB mSATA SSD drive for XEN on the mPCI slot.
As well as a 120GB 2.5" SSD drive for windows, 2x 1TB 2.5' Seagate FreePlay Drives for NAS, and a 500GB 2.5" WD Black drive for Firewall/Web Cache/other VM's all running off the motherboard's SATA Power Daisy Chain.
Im also using both the HD2500 IGD on my CPU(i5-3470S) and the HD7850.
The HD2500 is used for XEN's Dom0 and the HD7850 is passed through to the windows VM.
Im only using a 120W power brick for the motherboard too. The second PSU only powers the HD7850.
I hope this info helps you. Id say go for it, just make sure your circuit for powering the second PSU on is up to scratch before you use it with the GPU.
Oh. I will also mention that I have turned the pc on without the second PSU being turned on and no damage was done.