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AMPS for 6850?

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November 27, 2010 3:26:21 PM

hi how many amps will i need on my 12v+ rail in order to run a CF of 2 6850??

More about : amps 6850

November 27, 2010 4:17:42 PM

Crossfire? You'll want at least 40 on a single rail.
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November 27, 2010 7:45:13 PM

shadow187 said:
Crossfire? You'll want at least 40 on a single rail.

A pair of 6850's are only going to need about 12amps for the pair, where did you get 40 from?
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November 27, 2010 8:06:43 PM

Mousemonkey said:
A pair of 6850's are only going to need about 12amps for the pair, where did you get 40 from?


and where did you get 12 amps from?
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November 27, 2010 8:09:31 PM

ortoklaz said:
and where did you get 12 amps from?

Why, how many amps do you think a 6850 requires?
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November 27, 2010 8:21:30 PM

you still didn't answer the question
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November 27, 2010 8:25:08 PM

ortoklaz said:
you still didn't answer the question

You answer mine first, how many amps does a 6850 require on the PCIe 6 pin?
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November 27, 2010 9:07:44 PM

At reference speeds crossfired HD6850s tend to use approximately 250w under stress testing. I'd bump that up to 300w if you are going to be doing some overclocking. Power = Voltage x Current so the cards will use 300w/12v = 25a. That is for the cards alone however and the PSU needs to power the rest of the system as well. 200w is a good estimate for the max the rest of the system is likely to ever pull even if it is high end and I'd throw on another 100w to give some overhead for the PSU to operate efficiently and to account for capacitor aging. Basically a 600w or above PSU from a quality brand like Corsair, Antec or Seasonic would be a good choice for crossfired HD6850s. Here are some options;
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Or wait until "cyber" Monday and see if you can spot any good deals.
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November 27, 2010 9:11:59 PM

jyjjy said:
At reference speeds crossfired HD6850s tend to use approximately 250w under stress testing. I'd bump that up to 300w if you are going to be doing some overclocking. Power = Voltage x Current so the cards will use 300w/12v = 25a. That is for the cards alone however and the PSU needs to power the rest of the system as well. 200w is a good estimate for the max the rest of the system is likely to ever pull even if it is high end and I'd throw on another 100w to give some overhead for the PSU to operate efficiently and to account for capacitor aging. Basically a 600w or above PSU from a quality brand like Corsair, Antec or Seasonic would be a good choice for crossfired HD6850s. Here are some options;
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Or wait until "cyber" Monday and see if you can spot any good deals.

A single card uses 104.1w in the OCCT GPU test.
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November 27, 2010 9:15:28 PM

Mousemonkey said:
A pair of 6850's are only going to need about 12amps for the pair, where did you get 40 from?


Was playing more safe, I went with 14-14-12 card/card/processor. Then again, maybe I shouldn't factor in OC's.
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November 27, 2010 9:24:07 PM

shadow187 said:
Was playing more safe, I went with 14-14-12 card/card/processor. Then again, maybe I shouldn't factor in OC's.

A reference 6850 uses about 6 amps on the PCIe under normal gaming conditions and about 7 amps under stress testing so 12 amps on the 12v rail is enough for just the cards. I don't count the couple of amps from the PCIe slot though as that is a different connector.
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November 27, 2010 9:25:05 PM

Mousemonkey said:
A single card uses 104.1w in the OCCT GPU test.

Techpowerup got it up to 129w in Furmark;
http://www.techpowerup.com/reviews/HIS/Radeon_HD_6850/2...
Guru3D agrees with my numbers;
http://www.guru3d.com/article/radeon-hd-6850-6870-cross...
But I was actually using this which is a useful aggregate of all the major reviews available;
http://forums.atomicmpc.com.au/index.php?showtopic=264
Scroll down (a lot) or do a search for "6850" for links to the four articles they used for CF HD6850s.
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November 27, 2010 9:34:19 PM

Mousemonkey said:
I don't count the couple of amps from the PCIe slot though as that is a different connector.

This makes no sense.
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November 27, 2010 9:41:46 PM

jyjjy said:
This makes no sense.

It makes more sense than 250w needed for two cards.
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November 27, 2010 9:48:10 PM

Mousemonkey said:
It makes more sense than 250w needed for two cards.

No, it makes no sense at all. Care to give any reason what so ever that isolating the power draw on the 6-pin connector alone would matter to any one other than as a curiosity?
As for my numbers not making sense I gave links. Do you have an issue with techpowerup or guru3d? Perhaps some sort of advanced power reading methods you've personally developed that show they don't know what they are doing?
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November 27, 2010 9:51:46 PM

jyjjy said:
No, it makes no sense at all. Care to give any reason what so ever that isolating the power draw on the 6-pin connector alone would matter to any one other than as a curiosity?
As for my numbers not making sense I gave links. Do you have an issue with techpowerup or guru3d? Perhaps some sort of advanced power reading methods you've personally developed that show they don't know what they are doing?

Just for you I'll repeat part of my last post.

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November 27, 2010 10:03:33 PM

jyjjy said:
Just for me? I'm honored :love:  I guess that makes it fine that you ignore my first question and roundly dismiss the multiple sources I gave for no apparent reason while clinging to one piece of data.

I dismiss the citing of the Furmark result as it's an unrealistic load that will never be replicated under normal use.
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November 27, 2010 10:06:02 PM

all i have to say is.. don't ever go for minimum power requirements or you will be asking for trouble and upgrading very soon
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November 27, 2010 10:11:03 PM

I usually count the whole draw, not minus the pci, since it all has to come from somewheres
Id also add 25% to those numbers for a safety factor or upgrade
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November 27, 2010 10:26:52 PM

Mousemonkey said:
I dismiss the citing of the Furmark result as it's an unrealistic load that will never be replicated under normal use.

Do explain to me the difference between OCCT and Furmark that makes you think one is realistic and the other isn't. Reply to the 6-pin question at your leisure.
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November 27, 2010 10:36:03 PM

jyjjy said:
Do explain to me the difference between OCCT and Furmark that makes you think one is realistic and the other isn't. Reply to the 6-pin question at your leisure.

OCCT is closer to what you would see with an overclock whilst Furmark is what ATI/AMD and Nvidia both refer to as a heat virus and as for the 6 pin, if you look at the chart I posted you might notice the the 6 pin has the highest amperage draw which would suggest that the card takes most of it's power from the the 6 pin connector not the PCIe slot.
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November 27, 2010 11:15:23 PM

OCCT is designed to test the stability of an overclock, not emulate the power usage of a card with an overclock. Personally when choosing a PSU I'd get something that can cover all possible scenarios which perhaps is the reason most professional websites list the power usage numbers for Furmark or similar programs.
What you say about the 6-pin is true but why it matters still escapes me. You told the OP a pair of 6850s is only going to use 12a which is simply incorrect even if you are going to keep the cards at reference speeds and ignore stress testing and that the rest of the system needs power as well.
The chart you used is from xbit and they actually did an article on crossfired HD6850s. Here is the relevant chart from that article;
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November 27, 2010 11:24:08 PM

^+1
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November 28, 2010 12:56:41 AM

xBitlabs says the HD6850 uses 90W on Crysis.
Anandtech says an OC'd (940/10..something) 6850 uses 30W more than stock.
120W.
120W / 12v = 10a. 10ax2 = 20a. Add in 10 for CPU.
+12v of 30a minimum, 33a preferable.

Right?
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