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Old January 6, 2009, 06:58 AM
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Default Running a 4870x2 and a 4870 in tri fire?

A review at 3d guru shows the system load of several systems under full load with different graphics cards.

Radeon HD 4870 X2 and Crossfire review

HD 4870 .................... 334 watts
HD 4870x2 ................. 437 watts

this detailed thread shows the max power consumption of graphics cards alone. (by adding the wattage provided by the various connections and he max that can flow through these connections)

http://mark.zoomcities.com/images/gf...rchartby3d.png

HD 4870 .................... 130 watts (max)
HD 4870x2 ................. 264 watts (max)

so, using these numbers, i can roughly find the amount of power left to run the rest of the system. And if both match roughly i can continue.

4870 system - 4870 = 334-130 = 204 left for the system
4870x2 system - 4870x2 = 437- 264 = 173 left for system

ok, so ill just take the higher value to be safe.

add the power of the cards alone

4870 + 4870x2 = 130+264 = 394 watts

if im running with a 750 watt power supply at say, 80% efficiency at max load (my tx750)

that leaves (750*0.8)-394 = 600 - 394 = 206 watts left for the rest of the system.

so, does this seem right to you?

my system is similar to the one used in the 3dguru review, even the e8400, but mine is overclocked.

so, do you think i can run a 4870x2 and a 4870 in crossfire with my corsair tx750? rest of system specs in sig. keep in mind this is with the graphics cards and everything else at full load.


edit: just learned something about a psu efficiency, it should work from what i learned.
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Last edited by BrianHanna; January 6, 2009 at 08:03 AM.
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Old January 6, 2009, 08:26 AM
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My System Specs

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Your calculations are correct, but one of your assumptions is wrong.

A power supply's rating is it's output rating, not input. So a 750watt power supply can put out 750 watts, but will draw more from the wall depending on it's efficiency.

Better news for you, anyway, because it means more headroom. There's guys on here who've run an OC'd quad with 2x GTX280's on a 750watt PSU.

Edit: Sigh, you cross posted the same question in 2 forums. Don't do that please.

Last edited by SugarJ; January 6, 2009 at 08:35 AM.
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Old January 6, 2009, 07:57 PM
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Quote:
Originally Posted by SugarJ View Post
Your calculations are correct, but one of your assumptions is wrong.

A power supply's rating is it's output rating, not input. So a 750watt power supply can put out 750 watts, but will draw more from the wall depending on it's efficiency.

Better news for you, anyway, because it means more headroom. There's guys on here who've run an OC'd quad with 2x GTX280's on a 750watt PSU.

Edit: Sigh, you cross posted the same question in 2 forums. Don't do that please.

yea, sorry aout that. =(
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Old February 14, 2009, 08:04 AM
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Default ok?

So has this been confirmed to be ok? If so what are your experiences with it?? Im thinking about doing the same thing with the same powersupply and the same oced 8400 lol
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