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Author Topic: Beginner's Guide To Voltage Tweaking Your GPUs?  (Read 5498 times)
gigabytecoin
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June 04, 2011, 07:03:24 AM
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So I have the over/under clocking down pat...

I can get a 5870 running at 950core/300mem up to ~420Mhash stable/running for days on a linux mining rig.

I can get the card up to 1000core/300mem (and push ~450Mhash) but only for a few minutes at most before the entire machine freezes up.

I assume that the cards need more power to function perhaps? The temperatures are just fine... In the 75Celcius range since it is a cool room.

Any idea how I can keep the cards at 1000core/300mem for an extended period of time? It does not make sense to me that they could sustain it for a few minutes.. with a decent temperature... but not for longer.

Any advice would be greatly appreciated!
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gigabytecoin
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June 05, 2011, 12:45:38 AM
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Do you use Windows or Linux?
With Linux, it's quite difficult to overvolt your GPUs, you'll need to flash the GPU BIOS (see my sig). On Windows, there are dozens of manuals floating around, just google it or scroll through my guide, it has a link to one of them somewhere in it.

That the crashing occurs later means that your GPU is running at it's limit and since load aloways fluctuates a little you are pushed over the limit randomly. And at one time it's too much for your GPU to handle and it freezes.

I am familiar with both operating system platforms.

I edit my bios files using RBE in windows, flash them to the cards using rbe or atiflash, and then mine using linux...

Are you saying that my GPU is running at it's "electrical" limit and I could possibly increase that?

Basically I am an overclocking newb who is comfortable playing with core/memory clocks but am unsure as to what will allow me to increase my core clock to a higher speed and keep it stable. If the temperature is ok... power seems to be the only inhibiting factor in my mind no?
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June 05, 2011, 12:50:13 AM
 #3

go over to http://www.overclock.net/amd-ati/

lots of pros over there ready to help you. Just don't mention bitcoin, they banned it a few weeks back. Say you need help overclocking your 5870 and tons of people will be willing to help you.

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June 05, 2011, 02:47:06 PM
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It is worth noting that lots of miners actually undervolt their GPUs, so they use less power, as opposed to the gaming community who overvolt to get the max speed out of them.

The logic is as follows:

V=IR and P=IV=(I^2)R.
R is constant so I is proportional to V. i.e. I rises by the same percentage as V, when you over or under volt.

Increasing the voltage by 20% may increase your hash rate by 10%, but it will increase your power costs by 44%. (1.2 x 1.2 = 1.44)
Decreasing the voltage by 10% may not affect your hash rate, but will reduce your power costs by 19%. (0.9 x 0.9 = 0.81)

So, the 10% increase in hashing by overvolting costs 72% more in electricity than undervolting for the original hash rate.

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