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500w PSU for 5770 CF ?

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March 18, 2010 4:28:25 PM

Ok gentlemen. I am considering to purchase second 5770 for my rig. The question is - will my power supply suffice? I know that official requirements for 5770 cf is 600w minimum, but official requirements usually overrated. Is there anyone running 5770 in crossfire on 500w PSU? This is my configuration:

I5 750 @ 3.2 (160x20, stock voltage)
Biostar T5 XE CFX-SLI
4gb DDR3 1600 Gskill Ripjaws
1 Sata HDD 7200rpm
2 LED 120mm Case Fans
Thermaltake TR2 500w PSU
XFX HD5770
BD drive

PSU calculator says that with 2 5770s my total power consumption would be 289 watts (90% load)

here is link to my PSU specs:

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

More about : 500w psu 5770

a c 248 ) Power supply
March 18, 2010 5:08:47 PM

Here are the official ATI power supply requirements for the ATI Radeon HD 5770 and 5750 video cards:


450 Watt or greater power supply with one 75 watt, 6-pin PCI Express® power connector recommended

600 Watt or greater power supply with two 75 watt, 6-pin PCI Express® power connectors for ATI CrossFireX™ technology in dual mode

The recommendations are for an entire pc system.


Corsair and Seasonic are two brands that have a reputation for high quality power supplies that consistently earn high marks in technical reviews. They are reliable, stable, and come with a 5 year warranty. Some of the newer models come with a 7 year warranty.
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March 18, 2010 5:09:12 PM

I think you should go for at leas 550w
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March 18, 2010 5:41:20 PM

Thank you for quick answers guys. I know about the official ATI power supply requirements, But as far as i know usually they are overrated, even if you follow official requirements - not all of 600w psu's are same i guess. In fact there is a people who run 5770 CF on 500-520w PSUs, i have found couple of threads on different forums. I would like to know if someone has PSU same with mine. By the way my thermaltake TR2 has 5 years of warranty as well.

The thing is that upgrading PSU would mean spending another lets say $70-$80 which i would like to avoid unless its really necessary.
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a b ) Power supply
March 18, 2010 5:49:20 PM

The ThermalTake TR2 500W only has 420W max available to the +12V rails which won't be enough for two 5770s. Furthermore that PSU doesn't have two PCI-E connectors.

You'll definitely need a new PSU.
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a b ) Power supply
March 18, 2010 5:52:04 PM

Sorry, I lied about the PCI-E connectors...it does have two!
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March 18, 2010 5:56:53 PM

how many watts on +12V rails do i need?
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March 18, 2010 6:05:35 PM

some one said to that its 650w+
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a c 248 ) Power supply
March 18, 2010 6:12:11 PM

Yes, the official recommendations are a bit overestimated. That's because the video card manufacturers know a lot of people insist on purchasing low budget, low quality power supplies of questionable performance. The ThermalTake TR2 falls somewhere between a high quality and a low quality psu. It is not a stellar performer but it is adequate.

You mentioned using the power supply in an Intel Core i5 750 system with two ATI Radeon HD 5770 video cards operating in Crossfire mod. I'm guessing you're a gamer. There is something you should know about playing games. There are some "intense scenes" in games that result in a sharp spikes in power requirements. Even thought the spikes are relatively brief, not all power supplies can handle the spikes, especially if psu temps start to rise. The end result is strange things happening on your lcd screen or a even a complete shutdown.

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a b ) Power supply
March 18, 2010 6:13:06 PM

According to this review a system with 2 5770s in CF pulls 390W at load. And that obviously changes according to what you have installed in your system.

http://www.anandtech.com/video/showdoc.aspx?i=3658&p=13

It's pretty borderline in my eyes. You may get away with it, you may not. I have that PSU myself, only an older model and that's where the confusion came from on my above posts. Mine only has the one PCI-E connector but yours appears to have two. I know if you look closely at the label on my PSU it says clearly that 500W is the peak output wattage and that 450W is the regular output. From my experience of that PSU it just doesn't seem designed to power two cards solidly. The choice is yours though :) 
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March 18, 2010 8:00:31 PM

Thank you gentlemen.
moody89, i have seen that review, And like you have said "that obviously changes according to what I have installed in my system". In their test configuration they had i7 920 overclocked to 3,33Ghz, which draws more power than my i5 750. To find out how much more is it - I actually went back to magical thermaltake psu calculator... and voila - it gave me 409w VS 340w(my system) at 100 load... and 365w vs 310w(my system) at 90% load....
It looks like it will be close to the edge anyways but i think i am gonna try...
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a b ) Power supply
March 18, 2010 8:57:33 PM

I5-750 with 5770 (my system) and running furmark draws about 300 W. Add about 100 Watts for a 2nd 5770 and that brings you to 400 Watts.

This is an 80% load on a 500 Watt supply. I would concur with Johnny, A corsair, or seasonic, would be OK. For most "good" PSUs my recommendation is no more than 60 -> 70% @ max load (I personnaly shoot for 50%). As load percent increase, so does heat and the potential for failure. There is a chance that the failure could also take out your other components depending on failure mode. Is it worth it - That is your choice.
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March 18, 2010 10:34:47 PM

Check this out - it looks like 2 5770s draw about the same power with 1 gtx275 which is 10 watts more than GTX260 (500w PSU requirement) and about 35 watts less than gtx285(550w PSU requirement)... What u guys think?

http://www.hexus.net/content/item.php?item=20684&page=9

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a b ) Power supply
March 18, 2010 11:44:23 PM

ekg84
I've no dought a 500 W PSU is above the power need. The problem is that you are about 80% of max (Note great at Idle as would probably be under 200 W.

Depending on how long you are at 80% depends on you. Also Johnny made a point about current changes. This is simular to In-Rush Current. Altho not identical, I do current inruch measurements for 3 PSUs connected to a satellite instrument. For a very short time the Current jumps to 3 x normal current. What Johnny stated is that if/when the load requirement change very fast, you will see a spike on the +12 V line, if you are sitting at close to 80%, this spike could put the current above the max - Granted the time is very short < milliesecond.

Just remember - He who plays with fire may get burned. Key word is may, you may be lucky and never have a problem, on the other hand two months down the road you may fine a dead PSU and Hopefully that is all. Me I'm not Irish so would not take the chance.
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a c 248 ) Power supply
March 18, 2010 11:52:11 PM

RetiredChief - Thanks for the explanation. :D 

I read an article about something very similar during gaming but I never bookmarked it for a reference. :( 
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a b ) Power supply
March 19, 2010 2:12:08 AM

Johnny
I would like to put a current probe on say the 6 pin PCI-e and look at it. I might do it but I would need to get like an extender cable, Cut and splice the 3 Positive wires so that there is only one wire that all the current goes thru. This is the reason I've not done it. Same-same for the 4/8 pin ATX connect to look at the change when you go from idle to max load on the CPU.
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