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following this question, I'm on a quest to finding the most appropriate power supply for me.

The eXtreme Power Supply Calculator only goes up to 4 video cards and does not account for underclocks and overclocks of the gpu.

Here's a rundown of what I'll have: GIGABYTE GA-F2A85X-UP4
AMD A4-5300 Trinity 3.4GHz
CORSAIR 2GB 240-Pin DDR3
Patriot Supersonic Boost XT 16GB
And finally I'm planning on getting 6xRadeon HD 5870

I'm aiming at underclocking the processor around 2.0 ghz, no need for it to run higher than that. I'm aiming to underclock the gpu's ram to 160mhz, and overclock the core clock to 1100mhz. Those are my optimal clock speeds.

Now each card requires 2 PCIe cables from the power supply. Are there any power supplies capable of running those 6 cards while having all the necessary cables? Can I use 2 power supplies? If so how does it work?

Basically I'm looking for suggested watts needed to run 6 cards at those clock speeds and for power supplies suggestions.

Every bit of help is appreciated.

Edit: Before anyone tells me I can't fit 6 cards on that motherboard, I'll be using risers with a custom open air case, 3 16x risers and 3 1x to 16x risers. (Bitcoin mining does not require a lot of bandwidth, such 1x is more than enough)

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Do you already have at least one 5870 to test with? That would allow you to test how much less power the card draws when under-clocked. ( Run a system with one card in it, run your bitcoin mining and measure power at the wall. Than UC and measure again. Add the power reduction number to the post). –  Hennes Apr 4 '13 at 19:34
    
I have a 5850 currently mining running core and ram at 950/350 mhz respectively, but have nothing to measure the power consumed –  Rayfloyd Apr 4 '13 at 19:36
    
To answer part of the question: Yes, you can use two PSUs, but you will need to make sure what power levels they can deliver on which rails. And all six cards can draw 75 Watt from the motherboard, which is supplied from a single PSU. That is a total of (6x75) 450 Watt which will need to come from a single PSU. You can supply the 12 volt, 6 pins power plugs from a second PSU or from the same PSU using molex to PCIe-power converter cables. –  Hennes Apr 4 '13 at 19:37
    
I read somewhere on the forums that a single rail power supply is recommended since the power needs to be constant, so I'll most likely go for single rail. What are the 75 watts delivered from? PCIe? So 2 6x6 pin single rail ~800 watts power supplies should do the job? –  Rayfloyd Apr 4 '13 at 19:41
    
Looking at the mining hardware comparison chart there is an entry for 6x5870 with mem downclocked to 300mhz and no overclock on the core rated at 1200 watts for the cards alone, so 1200 watts is probably not enough and I will require 2 power supplies. –  Rayfloyd Apr 4 '13 at 19:47

1 Answer 1

up vote -1 down vote accepted

Considering that one of these cards under a stress test uses more than 188 (stock clock) watts of power, you would need at least 1200 watt psu ( ide use 2 750 watt psu's) - hope this helps.

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Do you have any sources I could look at? –  Rayfloyd Apr 4 '13 at 20:07
    
guru3d.com/articles_pages/radeon_hd_5870_review_test,13.html just do the math :P –  dashboard Apr 4 '13 at 20:10
    
The 384 watts is including the rest of the computer though, it is said the card has a tdp of 188 watts hehe so 200 watts to be safe. –  Rayfloyd Apr 4 '13 at 20:13
    
true my bad :P so may be safe with 1 1200 watt psu? scary! –  dashboard Apr 4 '13 at 20:16
    
I was thinking about a 600 watts psu for 3 cards on it only and a 800 watts one for the rest –  Rayfloyd Apr 4 '13 at 20:17

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