Svennand, first of all let me thank you for this very detailed and informative post.
I read you “adventures” with mobo frying here on the forums so I know you have lots of first hand info and that makes this thread even more valuable.
Let’s see if I got it right. The most important thing is: if you have more than two cards, you have to use powered risers or you will fry your mobo for sure. An the reason is the power overhead sucked up from the PCIe bus. If you have the powered risers the additional power is taken from them (the molex or whatever is connected).
Am I on the right track?
Ok. So, keeping in mind that I decided to switch the 7870 for a 6970, I made some calculations:
Card – Power ----> Overhead
Gpu0 (HIS 6970) – 250 W ----> +25 W (8+6)
Gpu1 (Sapphire 6850) – 200 W ----> -25 W (8+6)
Gpu2 (Asus 5870) – 188 W ----> -37 W (8+6)
These are figures for Scrypt mining according to this page. I verified that those numbers are quite spot on.
So, looking at these calculations I should be good to go, am I right? The mobo should be capable of handling the overhead if I put the 6970 on a 16x slot. Even without the powered risers. Am I right?
If that’s not true, the card itself should burn the mobo even if used alone in the rig. BTW I will have to buy risers anyway so I will have no problem at all I think.
As for the second PSU, I just connect it and I’m ready to go. Good news!
Another thing. I am thinking of an “anti-dust” layout where the pc is “upside-down” to avoid becoming a dust ball in a week. Something like this (poor) sketch is representing. Is there any risk in this kind of arrangement (that I’ve never seen around…)?? Everything would be obviously nailed down with nuts and bolts and on the MoBo, only the CPU fan and the ram are present. I don’t see any side effect in doing this but I may be wrong.
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