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Will 650 watts be enough for 4870s in crossfire?

Last response: in Graphics & Displays
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May 16, 2009 11:16:36 AM

Currently i have this PSU


http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Now it does say, its xfire certified and all that, but when i look @ amd's site they say its only good for one 4870 not for 2

then i looked @ antec's website and did the calculator and even with 2 video cards and my set-up im only drawing 402 watts @ 85% load and even @ 100% load its only 446watts (continuous)

so i guess my only real question is will it be enough? i've heard from people that 700+ is the way to go for xfire, or am i ok ?



Btw im running an e8500@ 3.2GHZ
2 sticks of ddr2 ram
one hdd
4 120mm LED fans and one 200mm and a 92 mm fan on cpu heatsink
22x dvd drive/burner



i know antec makes quality PSU's but i ran into some extra cash and wanted to see what my options were for an xfire set-up
If i am unable to run xfire with 4870s i dont wanna have to buy another PSU as well. wouldnt be worth it @ that point.

Thanks for any input you guys may have.
a b U Graphics card
May 16, 2009 12:14:39 PM

You'd be OK. The Antec calculator gives you not the actual draw of the system but the recommended size of PSU for what you list as your system components.

It's less about the wattage of the PSU and more about how many +12V Amps are available for the CPU and GPUs.
The 650watts and ~45Amps of +12V power of the EA650 would be enough for what you're considering. Part of the reason you see recommendations for larger PSUs is to cover the "average 700w PSU and that group of enthusiasts who like cram a PC case as full of interesting stuff as possible, and then push it as hard as possible as well.
A smaller PSU could handle the power requirements but when PSUs are pushed close to their limits they tend to get louder as the cooling fan spins faster, bleed off more heat, among other things that can also happen to stressed parts.

For about the same price, maybe less after rebate, you could get the Corsair 650TX with 52Amps of +12V power.
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a b U Graphics card
May 16, 2009 12:17:05 PM

Whoops....just re-read the part where you already have the Antec PSU. I'm sure you'll be OK.
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May 16, 2009 12:19:57 PM

sell the 4870 and get a 4870 X2, they perform better and use less power and your PSU can support it.
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a b U Graphics card
May 16, 2009 12:23:31 PM


Here is the power consumption chart that shows 2x 4870s in crossfire. And using a power hungry quad core CPU as well.
Note that the 448watt draw was measured at the wall socket. If the PSU in use was running at about 85% efficiency then the system was actually using about 380watts of DC power. And PSUs are rated in DC power output.
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May 16, 2009 12:35:03 PM

WR2 said:
http://techreport.com/r.x/radeon-hd-4870-x2/power-load.gif
Here is the power consumption chart that shows 2x 4870s in crossfire. And using a power hungry quad core CPU as well.
Note that the 448watt draw was measured at the wall socket. If the PSU in use was running at about 85% efficiency then the system was actually using about 380watts of DC power. And PSUs are rated in DC power output.







Well all right im good to go then, I dont run a bunch of fancy things i have an Antec 900 case and thats about as far as i go with lights/fans, Not big on hdd's or any sort of raid config (my 500gig suits me fine)

And my sound is onboard so thats a non-issue and pretty much everything on my system is still stock (well cpu is @ 3.2ghz from stock 3.16 lol and i didnt up the volts)

Thank you for the helpful advice now i can go to bed.. been googling my eyes out for the last 3 hours on info but it was really conflicting.
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May 16, 2009 1:50:16 PM

WR2 said:
http://techreport.com/r.x/radeon-hd-4870-x2/power-load.gif
Here is the power consumption chart that shows 2x 4870s in crossfire. And using a power hungry quad core CPU as well.
Note that the 448watt draw was measured at the wall socket. If the PSU in use was running at about 85% efficiency then the system was actually using about 380watts of DC power. And PSUs are rated in DC power output.
That's news to me. Does that mean I can run 4870CF with my PSU? Wow!
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a b U Graphics card
May 16, 2009 2:46:03 PM

It's best to be safe and get a 750watt PSU...

650watt PSUs will be stressed if it has to run 2x4870s
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a b U Graphics card
May 16, 2009 3:25:35 PM

rags_20 said:
That's news to me. Does that mean I can run 4870CF with my PSU? Wow!
Check for yourself. Antec PSU calculator
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