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How much power is too much power

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June 10, 2009 5:15:38 PM

Just looking to run 2 Nvidia Geforce 9800GTX in SLI for a new i7 rig im building.

I'm looking at both the Corsair 850TX & 1000HX. Id like to get away with using the 850, it would save me quite a bit of money - what do you guys think ?

Tried using a PSU Calculator and it ran me up at 730watts or so, but how much is enough...

Feel free to ask for more info...

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a c 243 ) Power supply
June 10, 2009 6:10:14 PM

Toms did a review of he GTX295 in SLI on an I7 clocked at 4.0 using an 850 watt Coolermaster, I don't think you have to worry about running a pair of 9800's on a Corsair 850.
June 10, 2009 7:18:29 PM

850w is plenty, just needs 40a preferably 48a on the 12v rail. It's best to aim for a PSU that keeps you at 60-80% of its max sustained output due to efficiency.

On some 1kw models if you end up using like 1/3 of the total wattage the efficiency of the PSU will drop and you'll waste money.
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June 10, 2009 8:03:07 PM

I am running an i7 920 @3.8Ghz, a RAID array and 2 GTX 285s in SLI on the Corsair 850w power supply with no issues whatsoever.
a b ) Power supply
June 10, 2009 9:28:41 PM

jeanluclariviere said:
Tried using a PSU Calculator and it ran me up at 730watts or so, but how much is enough...


750W is also plenty.
June 10, 2009 9:59:58 PM

mmm - thanks for all the replies. Im glad i dont have to spend more than i thought i might have to!
a b ) Power supply
June 10, 2009 10:23:04 PM

Corsair's own psu finder says 850W unit for 2x9800gtx, i7 OC'd, 3 disk drives.
June 10, 2009 10:53:52 PM

Twoboxer said:
Corsair's own psu finder says 850W unit for 2x9800gtx, i7 OC'd, 3 disk drives.


There are a few reasons for that
1. They sell PSU's and they want as much money from you as possible
2. They are covering their ass because as PSU's age they start to lose efficiency and their max power output decreases
3. Not all PSU's are created equal

850 is plenty and I agree with the poster above that a 750w from a quality company such as Corsair or PC Power would be powerful enough.

June 11, 2009 2:01:50 AM

What is wrong with the 850HX?
a b ) Power supply
June 11, 2009 3:40:11 AM

ragsters said:
What is wrong with the 850HX?


Nothing.
June 11, 2009 6:49:46 AM

You could also get one GTX 275 for about the same price as two 9800GTX which will be about 40% faster than the two 9800 GTXs in SLI. And you won't have to worry about sli stuttering, heat, fan noise, and the power issue. Yeah and sli rig looks cool on the eyes but on the perfromance side, there are better options.
June 11, 2009 9:11:48 AM

hundredislandsboy said:
You could also get one GTX 275 for about the same price as two 9800GTX which will be about 40% faster than the two 9800 GTXs in SLI. And you won't have to worry about sli stuttering, heat, fan noise, and the power issue. Yeah and sli rig looks cool on the eyes but on the perfromance side, there are better options.

Are you trying to claim that a 275 will beat a pair of 9800GTXs by 40%? If so, that's complete garbage. The 9800s will walk all over the 275 in performance, as long as the SLI is working. I agree that if you are buying a new video card, the 275 is the way to go, but the pair of 9800s is still a very capable solution.
June 11, 2009 2:19:34 PM

I didn't mention it earlier but as a couple before me mentioned there are better solutions that 9800GTX SLI, the only way I would do that is if I had them already. Most X58 boards support both SLI and crossfire and here you could get the 4870 for about the same price as the 9800GTX.
June 11, 2009 6:26:04 PM

Thanks again for all the replies. The reason why I'd asked was because I already have one 9800GTX and figured it would cost me less to get another, than it would for a GTX 275 - and yes - SLI is very pretty :]

June 11, 2009 7:59:59 PM

jeanluclariviere said:
Thanks again for all the replies. The reason why I'd asked was because I already have one 9800GTX and figured it would cost me less to get another, than it would for a GTX 275 - and yes - SLI is very pretty :]


SLI is great when it works. Not all games scale well which is why most suggest you should get the single best card you can afford. The 9800GTX is overpriced which could actually work in your favor if you were to sell the one you have on craigslist or ebay and use the money you get toward a faster single card. Say you were to get $70 or $80 for it you could buy a couple 4850's and crossfire them and end up spending less money for the same performance. The cheapest 9800GTX+ on Newegg is $115 after rebate. Assuming you could get $70 for the card you have now it would give you $185 toward a new card. You could get a 4890 for around $160 or add about $20 to it and you could get a GTX275. The point is that there are a lot of options and you should look at several of them and figure out which is the best for you and will give you the best return on your money. Since the 4890 and GTX 275 are pretty much on par I personally find little reason to spend the extra $50-$60 on the 275.
June 11, 2009 11:30:24 PM

Read this please.

http://www.xbitlabs.com/articles/coolers/display/system...

This is a another very good article on ACTUAL PSU power consumption, not what a manufacturer of PSUs says. An i7 920 and GTX295 didn't even get close to 600W when CPU and GPUs were stress tested. With 2 9800GTXs, you should be able to get by just fine with a high quality 650W PSU. Although, a 750W would provide room for expansion later on. I bought a 650W and wish I would have gotten a 750W.
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