Do I need a new PSU for a 8800GTX SLI setp?

PSUs: The source of DC power for all components in the PC & often a big noise source.

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echn111
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Do I need a new PSU for a 8800GTX SLI setp?

Post by echn111 » Wed Mar 28, 2007 1:12 pm

Adding an 8800GTX and upgrading to a full SLI setup soon. My Seasonic 550 Energy+ (550 watts) is a solid performer and I'm not keen to upgrade it. Full set-up in my sig.

I've currently got both the GPU and CPU slightly overclocked (by around 25%) and am keeping all voltages as low as possible to meet this overclock.

Top priority is "silence" not power so I am ready to decrease my small overclock and reduce voltages. However, I will absolutely not go below stock speeds (as that defeats the purpose of having a decent system).

Do I need to get a new PSU?

disphenoidal
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Post by disphenoidal » Wed Mar 28, 2007 2:43 pm

No, you should have plenty of headroom.

kater
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Post by kater » Sat Mar 31, 2007 12:08 am

It'll be fine, no worries.See here.

And here's also what my local folks have been playing with:

Test setup:
Intel Core 2 Duo E6300 @ 2400
Asus Striker Extreme
Patriot 8000 XBLK 2x1GB
Foxconn 8800GTX SLI @ 6300/1000
Seagate 160GB Sata
+ WC cooling and stuff like cold cathodes etc.

Image

See? A 450W Topower handled it perfectly! Rock stable voltages, quiet running, etc. LINKY to test. It's in Polish, but it has lotsa pics with readings etc.

A very important thing - remember it's power at the socket so you have to multiply it by 0.8 to get real power use (PSU efficieny of 80%). So it gets even lower.

qviri
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Post by qviri » Sat Mar 31, 2007 12:17 am

300 watts from the wall at idle? I'm impressed.

EsaT
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Post by EsaT » Sat Mar 31, 2007 3:31 am

qviri wrote:300 watts from the wall at idle? I'm impressed.
G80 is one giant P.O.S. when it comes to idling, basing to what can be deduced from data/measurements in reviews one 8800GTX consumes around 60W at idle!

Oleg Artamonov
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Post by Oleg Artamonov » Sat Mar 31, 2007 2:39 pm

8800GTX alone = 132W full load, 70W idle.

1) Core 2 Extreme Q6700 (Kentsfield) @ 3.5GHz, ASUS Striker Extreme, 4*512MB DDR2-800, 2*GF8800GTX, 2*WD1500AHFD -- 442W DC (533W AC with 83% PSU efficiency -- Tagan TG1100) under full load (Stress Prime 2004 + 3DMark'06).

2) AMD "4x4" 2*Athlon64 FX-74 @ 3.0GHz, ASUS L1N64-SLI WS, 4*512MB DDR2-800, 2*GF8800GTX, 2*WD1500AHFD -- 612W DC (737W AC with 83% PSU efficiency -- Tagan TG1100) under full load (Stress Prime 2004 + 3DMark'06).

3) Core 2 Extreme X6800 @ 2.93GHz, 4x512MB DDR2-800, 1*GF8800GTX, 2*SATA + 1*SAS (15k RPM) -- 280W DC (350W AC with 80% PSU efficiency -- HEC 460W) under 3DMark'06.

~El~Jefe~
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Post by ~El~Jefe~ » Sun Apr 01, 2007 10:47 pm

your psu at 450+ watt draw will be loud for spcr standards.

Also, it is not only a matter of total wattage, but what wires can provide what wattage. MikeC talks about this somewhere in his more recent reviews.

My recommendation is a corsair 620 psu. its a seasonic with an extra kick yet quieter than a seasonic. I am using it on a non sli setup. its a sick psu.

two 8800gtx's in sli???

you will be able to run oblivion at 1600x1200 with full aa/af/hdr on at sick framerates :)

tell me where you live so I can borrow that rig from you when you arent home....

shunx
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Post by shunx » Mon Apr 02, 2007 2:58 am

Doesn't it seem risky to draw 440w from a PSU rated at 450w for prolonged periods, even considering the AC/DC difference?
~El~Jefe~ wrote:you will be able to run oblivion at 1600x1200 with full aa/af/hdr on at sick framerates :)
I wonder how well it can run 2560x1600 or 3840x1024 (3-monitors) with everything maxed.

floffe
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Post by floffe » Mon Apr 02, 2007 5:27 am

Quality PSUs are rated for the output they can sustain, hopefully even at 50C, while cheaper ones might be rated for peak output. So no, a Seasonic or similar drawing 95% of rated power continously should not be a problem.

christopher3393
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Post by christopher3393 » Mon Apr 02, 2007 6:37 am

Given the specs., I would feel safer w/ Corsair HX 620W or Seasonic 650 Energy Plus.

nici
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Post by nici » Mon Apr 02, 2007 7:49 am

His PSU can provide 492W on 12V so if he isnt running a 200W+ CPU it will be just fine still with plenty of headroom.

christopher3393
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Post by christopher3393 » Mon Apr 02, 2007 8:30 am

Yes, I guess I was trying to allow for power usage under full load with a 25% overclock. If each GTX is using 132W on full load, how much higher will power draw be with OC? Same question about cpu OC'd. The Laing pump will have to be working pretty hard, I imagine, but I don't know how much power it uses. I'm not disagreeing, just having trouble estimating max total system draw allowing for potential OC'ing. Throw in hdds, fans, etc.,etc., what would you figure?

disphenoidal
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Post by disphenoidal » Mon Apr 02, 2007 8:49 am

In theory, power consumption in CMOS ICs is proportional to fV^2. So, for a constant voltage, a 25% increase in frequency will require 25% more power. Increasing the voltage will increase the power requirement faster.

nici
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Post by nici » Mon Apr 02, 2007 10:04 am

In theory yes, but from what i've seen increasing clock frequency while keeping the voltage constant doensn't make much of a difference. Here's my Opty 165, it's AC comsumption from the wall so it's not very accurate but should give some idea..

2600@1.3v

IDLE: 115W
LOAD: 180W

1800@1.35v, stock setting

IDLE: 122W
LOAD: 170W


1800@1.3V

ILDE: 120W
LOAD: 163W


2800@1.4v

IDLE: 125W
LOAD: 212W

Why on earth do you want to OC 8800GTX in SLi anyway? One of them is good enough for 2560x1600, let alone two. But even if you assume they pull 160W each that still leaves ~130W for the CPU.

jaganath
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Post by jaganath » Mon Apr 02, 2007 10:28 am

In theory, power consumption in CMOS ICs is proportional to fV^2.
right, but that's only the dynamic(switching) power. There is also leakage and short circuit power, which probably don't change very much with frequency, hence:
from what i've seen increasing clock frequency while keeping the voltage constant doesn't make much of a difference.
leakage power is a big part of overall power these days.

disphenoidal
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Post by disphenoidal » Mon Apr 02, 2007 12:18 pm

jaganath wrote:
In theory, power consumption in CMOS ICs is proportional to fV^2.
right, but that's only the dynamic(switching) power. There is also leakage and short circuit power, which probably don't change very much with frequency, hence:
from what i've seen increasing clock frequency while keeping the voltage constant doesn't make much of a difference.
leakage power is a big part of overall power these days.
Yes, I should have remembered leakage currents, which are very significant. :oops: In fact, playing with Notebook Hardware Control gives me similar results to what nici had. That is, running different frequencies doesn't make a huge difference in power consumption.

Richdog
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Post by Richdog » Tue Apr 03, 2007 8:05 am

echn111 wrote:Adding an 8800GTX and upgrading to a full SLI setup soon. My Seasonic 550 Energy+ (550 watts) is a solid performer and I'm not keen to upgrade it. Full set-up in my sig.

I've currently got both the GPU and CPU slightly overclocked (by around 25%) and am keeping all voltages as low as possible to meet this overclock.

Top priority is "silence" not power so I am ready to decrease my small overclock and reduce voltages. However, I will absolutely not go below stock speeds (as that defeats the purpose of having a decent system).

Do I need to get a new PSU?
Why on earth do you need 8800GTX SLI? Are you a hardcore bencher?
~El~Jefe~ wrote: you will be able to run oblivion at 1600x1200 with full aa/af/hdr on at sick framerates :)
You can do that with a single GTX... easily...

EsaT
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Post by EsaT » Tue Apr 03, 2007 11:59 pm

Richdog wrote:Why on earth do you need 8800GTX SLI? Are you a hardcore bencher?
I would guess two of those are good for keeping house warm even when idling.

shunx
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Post by shunx » Fri Apr 06, 2007 2:36 am

Richdog wrote:
~El~Jefe~ wrote: you will be able to run oblivion at 1600x1200 with full aa/af/hdr on at sick framerates :)
You can do that with a single GTX... easily...
There are some outdoor scenes in Oblivion that can [bring] the GTX down to 30fps or lower even at that resolution, so having SLI would help. And then there will be the demanding DX10 games this year.

[edited for typo]
Last edited by shunx on Sat Apr 07, 2007 5:35 am, edited 1 time in total.

Erssa
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Post by Erssa » Fri Apr 06, 2007 3:13 am

shunx wrote:There are some outdoor scenes in Oblivion that can the GTX down to 30fps or lower even at that resolution, so having SLI would help.
Oh, I see, that makes the 550$ investment and added noise worth while.

echn111
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Post by echn111 » Fri Apr 06, 2007 7:30 am

Thanks for the replies. It looks like I could get away with my existing PSU. That means my main concern is now about the noise. My Seasonic PSU is quiet within my sound insulated case, but still the single noisest part of my system by far, and putting more load may make it unbearable in terms of noise by SPCR standards. Suggestions welcome if anyone has any ideas..perhaps watercooling the PSU...?

As for the questions on why SLI. Simple. It's a hobby. Why do audiophiles go for £4000 audio systems when they can get a £400 system that makes similar sounds? But the main reason is the challenge. It's (/EDIT) easier to make a low powered system silent - less effort is needed to keep lower powered (/end EDIT) components quiet. Likewise, anyone can have a fast overclocked rig that makes a bit of noise. But I just find it more challenging to build fast, powerful and silent systems. How many people have a "silent" 8800GTX SLI overclocked rig?
Last edited by echn111 on Fri Apr 06, 2007 8:04 am, edited 2 times in total.

echn111
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Post by echn111 » Fri Apr 06, 2007 7:48 am

~El~Jefe~ wrote:your psu at 450+ watt draw will be loud for spcr standards.
....

My recommendation is a corsair 620 psu. its a seasonic with an extra kick yet quieter than a seasonic. I am using it on a non sli setup. its a sick psu.
Will look into it if I can't figure a safe way to watercool my existing PSU...

Erssa
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Post by Erssa » Fri Apr 06, 2007 7:53 am

12Leonardo wrote:As I know Nvidia recommends 450W for GeForce7900GTX sli and ~550W for GeForce8800GTX sli. So If Nvidia doesn't lie you needn't new PSU at the moment.
Who cares, if he doesn't need it. It's not the point here. He doesn't need SLI either, but he's going for it, and since this is SilentPCReview, I'd suggest getting another psu (corsair) to prevent the Seasonic PSU from ramping up to full rev. I think these are the kind of machines that were the inspiration for Antec P190.

nici
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Post by nici » Sat Apr 07, 2007 4:00 am

Don't start with the audiophile argument, that never ends well.. :lol: Good audio gear doesn't get outdated, it has resale value and it lasts a lifetime, very much unlike a high-end PC. When you think about it that way, 4000€ is very reasonable in my opinion. A high-end gaming pc costs maybe about 2500€ and in five years you have to pay someone to take it away.

That being said im not going to stop you from going with SLI, jsut make sure you really need it.

You might want to consider one of them new 500W passive SilverStones if they become available soon. Or maybe two normal PSUs, that would be a lot quieter at full load thatn just one since you would only be drawing an overestimated 250W max from each.

shunx
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Post by shunx » Sat Apr 07, 2007 6:20 am

Your system is quiet now because it's under 300w load so the PSU noise stays under 25 dBA@1m. But after you add the 2nd GTX the power will hit 400w. That will spin the fan up to 9V and the noise will be 36 dBA which is quite loud:
http://www.silentpcreview.com/article656-page4.html

So as far as the silence priority goes you can not get away with that PSU as it is. I think watercooling the PSU would be too risky unless one is very experienced. A 500w passive PSU sounds interesting but airflow will probably be an issue. The promising solution is probably running dual PSUs, but I've read that voltage stability may be a problem. (I'm still trying to learn about that myself, anyone wants to explain?)

shunx
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Post by shunx » Sat Apr 07, 2007 6:27 am

In any case I'd go for the Corsair HX620W since it was tested to be 29 dBA@1m at 400W which would be borderline quiet.

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