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Recommended PSU for SLI

Last response: in Components
November 28, 2005 7:24:55 PM

How the hell is everyone? I've been gone a while, but I'm back to help all the n00bs with their questions. I figured I'd give Wusy and Crashman a break.

Anywho, I have a n00b question myself.

I just got 2x XFX 7800GTX Overclocked cards for SLI. My PSU is rated at 485 watts (it's an Enermax). nVidia and company recommends a 500 watt PSU for SLI. Anyone in here have a similar setup on a <500 watt PSU? I don't really wanna go blow another $100 to get 15 extra watts if I don't have to... esp since this one's only 6 months old.

I expect a reply from such dirty bastards as dhlucke, wusy, and crashman.


More about : recommended psu sli

a c 158 ) Power supply
November 29, 2005 1:32:18 AM

We haven't seen Wsuy since the forums changed to ForumZ. Not sure where he's hiding. Crash and DH are still around and I'm sure they'll stumble on this thread soon.

Do you have the EG495AX or the EG495P? If so, then either is probably sufficient. Stress it with benchmarks on install to check for stability and log voltages for spikes. It would be my first suspect if instability reared its ugly head, but it's worth trying.

Welcome back to the boards. Wingding is waiting with baited breath in the "Other"...
November 29, 2005 10:44:13 PM

Well, it seems to be working fine w/ this 485W PSU. I played some pretty demanding games and the system is stable- no issues. However, I've yet to hook up some of my USB devices and 2 more hard drives- that'll be the true test.

For those of you out there considering going w/ SLI- 485W is enough with this configuration:

Athlon X2 4200+
2x XFX GeForce 7800 GTX's (factory overclocked)
2x WD Raptors in RAID configuration
4x 256MB DIMMs (DDR400)
Asus A8N-SLI motherboard
2x DVD/CD burners
1 Linksys wireless NIC

Related resources
November 30, 2005 1:09:37 AM

I'm certain you're in fine shape.

1) nVidia has to assume you have crap for a PSU. Enermax isn't crap.
2) nVidia has to assume you're using a P4D840EE. An X2 doesn't use nearly that much power.

I'm too lazy to go search, but some power consumption thing I read recently had an X2 pulling about 100w less than a P4 - gahh, I'm gonna have to look it up... that sounds outrageous at first glance... Anyways, the X2 pulls around 215w I think - maybe up to 235-ish - and add another 50w or so for the xtra 7800 (don't know what they use...) you're still well under 70% load on the PSU.

a c 158 ) Power supply
November 30, 2005 1:23:02 AM

485W of Good PSU - which model is it?

That's a fucking sweet rig! What monitor are you using - Dell 2405? How many banks are on your RAM - you having to loosen the timings or command rate?
November 30, 2005 1:29:01 AM

Looked it up - TechReport, Toms, and a couple others all have the X2 4800 about 200-225w with some video card - 6800U at the high end. The 4200 was about 25w less. You've got plenty of room.

November 30, 2005 4:01:17 AM

The monitor ain't all that great... it's an Hitachi CM721F (19 inch CRT). That's the next thing i'm going to upgrade. :-D Thinking of getting that Hitachi 19 inch LCD the site reviewed a few months ago. Newegg has it for $279. 12ms response time- good enough for me.

I've got 4 banks all filled with 256MB DIMMs. It's the Corsair 3200LLPT TWINX stuff. 2-3-2 timings. Right now they're still timed at CAS2 and I'm overclocked to 2.4Ghz w/ Hypertransport at 880mhz. Stable as hell. Haven't loosened timings... yet. >:-D It's funny cause I've had this RAM since 2003 and it's still going strong. I paid a fortune for it when it came out, $450 I think. It's like $200 for 1GB now.

I'm considering selling the processor on eBay and upgrading to the X2 4800+. I'm selling my old rig on eBay (P4 3.4Ghz, MSI 865PE, Radeon x800 Pro) and if I sell this processor I'll have the $700 needed for it.

I'm completely retarded.

November 30, 2005 4:02:27 AM

That's wierd cause AMD's site has the x2 4200+ rated at 85 watts. They're probably full of crap though.

a c 158 ) Power supply
November 30, 2005 10:16:50 AM

RAM has dropped like a rock and tighter timings have become a lot more common. With Samsung TCCDs and Micron's chips, competition has done us a favor. :smile:

I haven't looked at the Hitachi much - I'll give it a read...
November 30, 2005 1:59:09 PM

Naw, that 85w is the maximum the CPU alone will ever draw (that's the way AMD does it - Intel is defined differently). Add 25 or so for the mobo, 15 each for hard drives, a few for mouse & keyboard, video card, etc., and you get the real number.

November 30, 2005 5:35:17 PM

I woke up this morning to find my PC off. I immediately considered the possibility that the PSU gave up on me. But when I looked around my room- everything else was off.

My PC actually tripped the breaker! LOL. Now that's power. :twisted:

November 30, 2005 5:37:57 PM

Yesssssssss! :twisted:


December 1, 2005 11:30:36 PM

I'm fashionably late. :D 
December 2, 2005 3:29:55 AM

Well this is my setup and I've had some issues with SLI and a 480 PSU.

Athlon 64 3700
XFX 7800GTX 256
NeoPower 480 PSU
Creative X-Fi soundcard
3 gigs RAM (2- 1gig 2-512mb)
Plextor DVD R/W
WD Raptor 74gig
WD 160gig

When I plug in the second 7800GTX the system doesn't see all my ram, it only sees 2.5 gigs. I am guessing this is because the PSU can't power all of it. What do you think?
December 2, 2005 3:42:00 AM

That's wierd. I have a nearly identical setup as yours. Only real difference is i've got the OC'd cards which eat more watts and you've got more RAM. But then again, I'm using all 4 of my banks. You would think that mine would have issues too. Maybe it's that extra 5 watts that puts me over the top.

I think you're right in surmising the mobo can't see that other 512MB of RAM cause it's not getting enough power.

I guess my PSU is at it's extreme limit then. LOL. I won't be adding any more crap to this baby till I get some dinero for a new PSU. :-D

Uh, replacing PSU's are such a hassle. Have to re-cable everything and re-ziptie everything. Not looking forward to it...

December 2, 2005 3:51:51 AM

While Antec makes good psus The Neopower isn't as good as the Truepower, so it could be just over the edge of stability for that PSU.

I gues its possible the PSU can't power up just 1 stick, but that sounds wierd. I would think it would manifest itself as just instability - or maybe not power up some RAM some of the time or something like that.

Does it recognize a full gig when you pull your 2 1gig sticks and just leave the 2x512 in? (just for testing of course) If so, then you could be right - if not there's some other reason for it.

December 4, 2005 12:19:40 AM

Okay here is what happens:

With a 480w PSU and (1) 7800GTX my mobo sees 3.0 gigs of RAM...

With a 480w PSU and (2) 7800GTX my mobo sees 2.5 gigs of RAM...

With a 600w PSU and (1) 7800GTX my mobo sees 3.0 gigs of RAM...

With a 600w PSU and (2) 7800GTX my mobo sees 2.5 gigs of RAM...

Maybe the ASUS A8N-SLI Deluxe can't handle the two cards in SLI and 3 gigs of ram. It can't be a PSU issue. Thoughts?
a c 158 ) Power supply
December 4, 2005 3:53:22 AM

Why do you need more than 2GB?
December 4, 2005 5:29:49 PM

1) I payed for it.

2) I do a lot of intensive graphics work and it eats ram like theres no tomorrow.
a c 158 ) Power supply
December 5, 2005 12:49:02 PM

Intensive graphics work - got it. Most people do not have a valid need/reason for more than 2GB - or even 2GB.
December 5, 2005 12:56:20 PM

TAKE THAT BACK!! I need ATLEAST 2GB, and i am considering 3 or more, for my 6600GT and A64 3000+ to play BF2....i want to spawn first.
December 5, 2005 2:56:52 PM

I agree - not the PSU. Maybe it is something with the mobo, but I'm just guessing...

December 5, 2005 3:52:43 PM

Maybe it's the fact that my northbridge chip is 55-65c and it just goes retarded and can't handle the ram.
December 5, 2005 7:59:10 PM

This is almost certainly a flaw in the motherboard. I would check Asus's website and see if there's a BIOS fix for it. If not, notify them of the problem. I doubt it's a temp issue cause my board runs that hot too. It's the shitty heatpipe design they're using.

I guess I won't be getting anymore than 2GB in the future w/ the board. :-)

a c 158 ) Power supply
December 6, 2005 12:38:43 PM

:/  - NO