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Old January 6, 2009, 04:30 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.
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Old January 6, 2009, 07:05 AM
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Originally Posted by BrianHanna View Post
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.
Ops, you're wrong on calculating efficiency. Efficiency is the conversion result from AC into DC.
With other words your PSU is rated at 750W DC and for 80% efficiency it will draw 938W from the wall (of course at full 750W load).
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Old January 6, 2009, 07:51 AM
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Originally Posted by burebista View Post
Ops, you're wrong on calculating efficiency. Efficiency is the conversion result from AC into DC.
With other words your PSU is rated at 750W DC and for 80% efficiency it will draw 938W from the wall (of course at full 750W load).
o, so lemme get this straight, my psu will always give me 750w? im sure thats not right.


EDIT: after doing some research i found out that you are correct, wow, how could i not have know that.


so my psu should def be able to handle it amirite?
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Last edited by BrianHanna; January 6, 2009 at 07:59 AM.
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Old January 6, 2009, 07:59 AM
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Not always 750W. Just what you need until 750W.
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Old January 6, 2009, 08:01 AM
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Not always 750W. Just what you need until 750W.
no, i got that, was just trying to understand, i though the power loss happened in the psu, not from the wall to the psu.


so at max load my computer will be getting it's 750 watts, but i'll be taking more from the wall.
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Old January 6, 2009, 08:35 AM
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so at max load my computer will be getting it's 750 watts, but i'll be taking more from the wall.
That's correct.
Quote:
Originally Posted by BrianHanna View Post
so, do you think i can run a 4870x2 and a 4870 in crossfire with my corsair tx750?
I'd say that you're OK but if you don't mind may I ask you why? For a 22" LCD and a E8400 (even OC'ed) one HD4870 is OK, one HD4870X2 is overkill and what you want to do is just a waste of money and power.
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Old January 6, 2009, 08:49 AM
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That's correct.

I'd say that you're OK but if you don't mind may I ask you why? For a 22" LCD and a E8400 (even OC'ed) one HD4870 is OK, one HD4870X2 is overkill and what you want to do is just a waste of money and power.
i know, i have this thing where i want what i dont need. im trying to talk myself out of it, and save the money.
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