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What PSU requirement is needed for this cheap setup :

• Used EP45-UD3L mobo
• E5200 CPU
• USB key for SMOS linux
• Wifi Dongle
• 5 x Sapphire Dual-x 280x GPU

My own measurement would be 200 watts for the mobo/cpu/usb stuff and 1500 watts for the GPU. So total would be 1700.

I am being too conservative here ?

would be easier to do 2 psu to reach that i would probably put the mobo and 2 gpu on a 750w and the 3 gpu on a second 750

that said newegg has the corsair hx750 on sale for 109 after rebate if you have the newsletter they send out there is a promo in there for another 20 off to make the 750w psu 89.99.

Thanks Lunas. So you think the Sapphire card would draw less than 300w each ?

Overclocked they can do over 300w but I reckon theyll be around 250w. Maybe lower with some undervolt.

You still need to figure out if youre going to cut the powered risers which im assuming youre going to get. If you arent going to cut them then youd need to run all risers on the same psu as your cpu/mobo and that psu need to be able to handle that. This is important, running some risers on one psu and some on another will result in catastrophic failiure unless you cut the 12v feeds on the riser-cable.



Even if you do cut the risers and run 3 full gpus on each psu then Id say 2x750 is on the low side. Especially for the one running cpu/mobo.

I run 5 sapphire 280x dual-x but I use 3 psus.
850w: cpu/mobo+all p.risers+1x280x(6pin+8pin)
750w: 3x280x(6pin+8pin)
400w: 1x280x(6pin+8pin)

Obviously the 400w is overkill but i had that one lying around so figured id use it and save a few bucks. But yeah thats about as far as I would go on 850w and 750w together (both corsair btw).

If youd want two psus and run five cards then I would probably do one 850w and one 1000w and use the same config as I did above except you run four of the cards 6pin+8pin on the 1k psu.
Skimping on power isnt something youll want to do.



Edit: you can see my calculations here: https://bitcointalk.org/index.php?topic=441927.msg4856476#msg4856476
They are on the safe side so you might be ok with less but I wouldnt like to bet on that with my money.
It could work with 2 cards on the 850w I guess, if your peripherals dont draw much and the powered risers dont draw the full 75w from each but like I said. Better safe than sorry.

Many thanks hyperionx. My risers have a molex power cable.

But what do you mean by 'cutting the powered risers'? Can you explain a bit more on that?

I have 4x Sapphire 100363L r9 280x doing 730 KH/s each on BAMT miner with the voltage modded to 1.050v, I measure the power draw and it was 990 to 1005 watts. :P I am using a 1200w PSU

Are you counting only the GPU's? I bet you are, but I only want to make sure. ;)

Why does the risers molex have to be on the same PSU than the mainboard?

Problems can sometimes arise if you don't.  The mobo draws that power normally without risers, so when you use risers it is suitable to continue that task for the mobo psu.

I just want to make sure since I don't see the logic there.. the risers have to be connected to same PSU than the mobo, but it can be different PSU that the one the GPU are connected? Is it absolutely necessary? What have to be taken care of if you can't?

Dual 750W should work for your setup. I believe if you time the starting of the 2nd PSU properly with the first, you may be able to avoid some problems with powering the powered risers with the PSU that is not powering the mainboard.

1500 should be enough for 5 GPU.

280Xcan draw up to 300W so 1600W good psu or 2 smaller 1000 will do the thing.