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Old September 5, 2011, 06:39 PM
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hey I am getting my hands on 3 5770's and wondering if my 700watt modxstream OCZ psu will do?
I would think so but want to make sure. And would like any help in teaching me how to tell what psu will do. Any info or links will help thanks. We all had to learn somehow.
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Old September 5, 2011, 07:01 PM
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Bad idea, get another PSU.

I'm also ignoring the bad rep that OCZ PSU's get around here when I say it's a bad idea.

That unit can barely put out 500W on the two 12v rails, 3x 5770 can easily draw ~350W alone without any OC, which leaves barely sufficient headroom for the rest of your system. (I'm assuming you're not using a low power CPU in a system like this) You also won't have enough PCI-E connectors, (you only have 2 out of a required 6 and adapters are generally not recommended) and you're likely to overload one of the 12v rails.

As for what PSU to buy, I would say that it would depend on what you plan on using the system for, how much you value energy efficiency, and how much you value modular cables.
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Old September 5, 2011, 08:33 PM
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http://www.guru3d.com/article/radeon...-review-test/3

they are saying around 750 watts

however they are saying 200 watts for cpu
your cpu uses under 100 watts (unless OC'd)

and really everything else in the system won't add up to another 100 watts


now i looked at you PSU
it has 2x 12 volt 25 amp rails

it has only 2 x 6 PIN for PCI-e
(5770's only use 1 6 Pin connector not 2)
the 3rd card would need a power adapter, not sure if it comes with the video card or not anymore

i would have 2 of the cards on the 2nd rail. since i believe the first one is used for CPU/motherboard as well
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Old September 6, 2011, 06:27 PM
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Quote:
Originally Posted by Jaydu View Post
hey I am getting my hands on 3 5770's
In performance per watt / performance per dollar you may be better off trading those three 5770s for a 6950 (don't know what price those are going for)...

Quote:
Originally Posted by Jaydu View Post
And would like any help in teaching me how to tell what psu will do. Any info or links will help thanks. We all had to learn somehow.
I'll walk you through how I look at this power consumption estimate...

I look at reviews of computers that are similar to mine and guess the watts from there. One of my starting points (hopefully there's an updated one with newer nVidia 5xx series out there) is reviews that measure power consumption at the interal power connector rather than between the wall and the PC like this one:
La consommation de 93 cartes graphiques ! - HardWare.fr

Add up the estimated wattage of everything in your system, and then make sure your PSU can deliver more power through its +12V rails than your estimate. If the PSU has more than one +12V rail, then you'll have to come up with multiple estimates for each rail. Generally you need to look at reviews to see what will suck power from which rail. This method works as long as you don't have a overrated PSU, which is to say the PSU can't deliver what it says on the label.

I agree with roh_ultima's estimate for your system - it concurs with the review I have linked.
Now I'm going to assume this power supply config, and that one rail is for the PCI-E connectors while the other is everything else:

Since GPUs suck power from both the motherboard and the supplemental connector, I'm going to assume the worst case for the total 100W of a 5770 with 75W sucked out of the motherboard and the remaining ~25W from the connector.

That means the "everything else" rail, +12v1, will have:
Two GPUs from motherboard: 75 x 2 = 150W
Third GPU doesn't take anything from +12v2: 100W
CPU (assume some overclocked quad): 150W
Motherboard / chipset / disks: 30W
Total = 430W

Then +12v2 has the 25 x 2 = 50W.

Trouble is... +12v1 provides 25A, or a total of 12V x 25A = 300W.

430W (what you may need) > 300W (what it takes on one rail to shut down the PSU)

So then my answer is nope, you shouldn't try it. I admit the estimate that the GPUs will draw almost completely from the motherboard is a little aggressive, but you want to make worst-case scenario estimates when you're talking about whether your power supply will overheat or not
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Last edited by frontier204; September 6, 2011 at 06:29 PM. Reason: typo
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Old September 6, 2011, 06:37 PM
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Why go with 3 low power cards and not 1 powerful?
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Old September 7, 2011, 08:45 AM
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I would vote to sell them too, you can probably get 60-70$ for each and buy a 560 Ti or 6950 with that.
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Old September 7, 2011, 09:03 AM
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I really, really wouldn't even attempt it with that PSU.
OCZ's have been my bane for the longest time, mind you the newer ones do look better but the older ones will die horrible deaths...

That being said, It really would make more sense to get yourself a more modern card rather than trying to scale 3 5770's.

My thoughts,

-ST
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