Double PSU mining rig
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Hi guys!
I have some spare time and decided to use it to group some old GPUs I have mining around in one small open rig with an old CPU/MoBo/RAM etc. I only have a 500 W PSU which is not going to be enough to power all the three cards, so I have two choices:
-dual PSU
-buy a bigger one
The cards are: 5870, 6850 and 7870 and together they’re going to need around 600 W more or less. I know I can make it with a 1000 W PSU but those cost a lot and I have 2x 500 lying around unused!
I found this video on youtube but there are some comments with guys reporting burning the MoBo etc.
I understand that the second PSU should only be linked to the 12 V plugs of the additional GPUs and all the MoBo related connections (risers included) should go to the first one.
But still these three are not exactly “crappy cards” I can sacrifice and would like to hear some first hand experience from people I trust.
Any advice?
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The reason people burn their mobo is mainly cause they add to many cards without thinking what kinda power those cards draw from the pci-e bus.
every overhead above what the socket on gpu can deliver (8+6 pins gpu can take up to 225w, 6+6 pin can take total of 150w). Meaning if the card actually use 300w it will get the remaining through the pci-e socket itself. Now if you have 5 cards which each have supply capability
of 225w, but need 250w. Your looking at an draw from the pci-e of 125W total, normally pci-e 1x is rated 10w, pci-e 16x is rated 25w, and total consumption combined should not go above 75w. 50w overload over time WILL melt your mobo.
Either the 24Pin power connector on the mobo will burn, or the lanes to the pci-e sockets itself (botton of mobo)
Heres an example on one of my old rigs (5879/6870 and so on)
https://www.youtube.com/watch?v=1KW7y4uGgYs
The only thing you need to do on the secondary psu is to use the 12v to the GPU (keep in mind that some PSU might take damage if its 100% loaded on 12v but nothing on 5v and 3v. Dunno exactly why but i read it someplace).
To get it startet you just shortcircuit two pins on the 24pin contact. like this:
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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.
