SLI newbie - unanswered question

dbunder

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Sep 11, 2005
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I've gone through the FAQs on here and read some guides and whatnot, but I'm still a bit unclear on some SLI stuff.

For instance, hypothetically, if I had one 7800GT running at 450 core, and another running at 500 core, would it work, or would it take the lowest common denominator and run both cards at 450? Or would I get the full 500 and full 450?

Also, again hypothetically, what is the REAL power needed for a 7900GT on the 12V rail? It's really hard to find specs that go that deep and tell you what it requires. I had a PSU picked out for my future SLI setup, and it looked perfect, then was told it wouldn't run even *one* of my cards (it was the Antec Truepower 550). Seemed like a really beefy PSU to me, but apparently not. The PSU issue is the most confusing part of the whole thing. I don't wanna go out, get a PSU that runs my cards and my drives and everything else, then later add a new HDD or optical drive and have the PSU not be able to handle it. Are the PSUs listed in the hardocp SLI FAQ still valid for a couple 7900GTs, a couple SATA drives, a DVD burner, 4 case fans (4 pin, so on the 12V rail), and good CPU and GPU cooling systems? It'd all be trial and error. And that's not something you wanna have error on. Fried components = bad news bears.

Are there any good, up to date sites that explain SLI setups and what you should have to get one up and running without having to worry about running out of juice? If someone could toss me a link or three, it'd be awesome.

What really confuses me is why video cards these days just don't have power jacks in them so you can plug them into your power strip instead of your PSU. :p It's just gotten that bad.

Thanks for any help/input. Sorry about posting so many threads around here today, but I just ran into a boatload of cash, and I'm prepping to upgrade to a new rig. Tasty!
 
you overclock both cards the same amount. You will end up with the lowest of the two cards ability to overclock.
 
Good to know. Thanks for the response. Anyone have any pointers for me on PSUs, and how much I should be looking for on the 12V rails? I've got my mobo and processor more or less picked out... next step is a PSU that can handle all my goodies *plus* 2 XFX 7900GTs with volt mods.
 
wee96 said:

Both are spendy, but I do love Enermax. Have had mine without issue for three years, but I'm fairly sure if I added one more device to it it'd implode. ;)

Was actually looking at the first two results here (mainly the first one): http://www.newegg.com/Product/Produ...&description=&srchInDesc=&minPrice=&maxPrice=.

Or would 19A on the 12V rails be pushing it? A few of the reviewers are saying they're running dual GTs/GTXs off it. But who knows? Maybe they've since fried said PSUs.
 
I would remover both these two, and get the enermax liberty 620 (bit better power, and single 120mm fan so quieter).
the pcp&c is probably the best of all, but costs more, louder and unneeded power.

f
 
What you might want to remember with power supplies is that name brand does matter...

an Enermax 550w or CoolerMaster 550w is NOT the same as some no-name power supply rated at the same wattage...You don't have to spend an inexorbant amount of money on a 650w psu, just don't skimp on the quality.

nVidia and ATi recommends at least 500w for current SLI systems...certainly nothing wrong with more wattage if you wish...I have an XFX 7800GT EE SLI overclocked system at 510/1.1Ghz with watercooling, dual slot drive optical, volt oc'd dual core processor, X-Fi, Dual tuner card, 2 HDD coolers, and dual Raptors...all on my RS550w Cooler Master SLI PSU...and it runs perfectly. The same PSU I use you can buy for $118.00...

Welcome to club SLI ;)
 
CMAN said:
http://www.newegg.com/Product/Product.asp?Item=N82E16817711002
This is the one i use,they also have a 600watt powerstream also. DOUG

This looks like an excellent choice. Been reading reviews, etc on it for a bit.

I know to be careful with brands of PSUs... that's why I'm running an Enermax right now.

I've always liked the modular PSUs, but I've never found one with enough power. Just found this one though... problem is, it's a brand I don't know. http://www.frozencpu.com/psu-163.html. Pretty sexy, but a no-name. Plenty of power on the rails, wattage, and SLI capable (don't know about certified). The price makes me a bit wary though.

There's also this http://www.newegg.com/Product/Product.asp?Item=N82E16817709004 which has been recommended by a friend, and talked about on these boards.

I know Antecs are good (the Truepowers), but have also heard warnings about them on various boards, including this one.

I think it comes down to the OCZ 520, the Sunbeam (if anyone can recommend it), or, in the very unlikely case that the modular one can be vouched for, that one. It looks solid... but I just dunno.

I'd like another Enermax, but the Liberty 620W is over my budget, the Liberty 500W may not have enough power, and the others (at least on newegg) don't seem like they'd provide enough power.

If it helps any, what I'll be running is either an AMD Athlon64 3700+ San Diego or an Opteron 146 (overclocked as high as I can get either stable), 1 250GB SATA1.5 HDD in the case, 1 250GB SATA3 in an enclosure running through eSATA, 1 Plextor DL DVD burner, a floppy, 2 sticks of PC3500 Mushkin 2-3-2-6 512mb memory, 1 XFX 7900GT with the conductive ink volt mod and possibly the pencil lead memory mod (again, overclocked as high as I can get it stable), and a DFI LP UT nF4 SLI-D Socket 939 NVIDIA nForce4 SLI ATX mobo, and possibly additional back USB2 ports, 4 LED 80mm 4pin case fans, some sort of VGA cooler (likely Zalman, but not sure yet), and a 120mm fan for the CPU cooler. Future upgrades would only include 2 more sticks of 512 memory, another 7900GT, and *maybe* another internal SATA3.0 HDD. That's all I can think of.

Excuse the long posts... I just want to get this right. Covering all bases. Oh... little aside. Does dual 12v really matter?

Thanks again :)
 
The OCZ powerstream also has adjustable voltage rails so you can dial them in. DOUG
 
You won't regret it. I have PC P&C units that are over 5 years old that have been running 24/7 with absolutely no problems ever. That said, I have had doa units from them also. They still get my business. Went to Antec for a while, they make very good products, but ended up going back to PC P&C for the quality and dependability.

I have been building / maintaining our company's computers for over 16 years. Have never regretted paying extra for PC P&C products. Their support is outstanding; when I did have some bad units, they replaced them very quickly.

Now using PC P&C 850 and 1kw units at work and home with heavily configured systems, such as Tyan S2895's with up to 14 drives and dual Opty 254's (2.8 ghz single core).

Like someone said before, you can't go wrong with a PC P&C 510 SLI power supply, either. Best mid-range psu available.

Interesting read:

http://www.pcpowercooling.com/about/interview.php
 
The OCZ PowerStream 520W is the most attractive thusfar for the price. The PC&Cs I *wish* I could afford, but it's a no go. Gonna look at a few more Enermax, OCZ offerings, and anything else anyone would recommend. Choosing a good/affordable PCU was the hardest part of my last build, and it's no different here. If Enermax offered a Liberty between the 500W and the 620W it'd be ideal, but no dice. I'm afraid the 500W wouldn't be enough power to run everything (correct me if I'm wrong). Same deal with their Noisetaker line. One too little, one too much.

I may, once again (like I did with my mobo choice), have to pluck 40 extra bucks from the nonexistant money tree and settle on one of the 600ishW Enermax offerings, unless people here are confident that the OCZ 520 would be sufficient for my components and very reliable. It's been the most suggested PSU to me so far (and the second most suggested at http://www.hardforum.com/showpost.php?p=1027898520&postcount=6), and that says something.

edit: noticed that Scythe offers a pretty damn nice 550W PSU (the Kamariki-2) at a good price. Since their CPU coolers are so highly rated, perhaps their PSU offerings are of similar quality? All of the reviews I've read have been positive. Only problem is it has only one fan, but I can go ghetto on it and strap a 90 or 120mm fan on the back of the case where the PSU's fan *should* be.
 
ClintE said:
The Enermax EG651P-VE FM is a nice looking psu, nvidia sli certified. I'm using one of their EG851AX 660w, rock solid so far. 140 bucks on AJump for the EG651P isn't bad:

http://www.ajump.com/ajump/product.asp?pf_id=4330026&dept_id=9200

I'm unable to find either even on enermax's site. Any detailed specs on those? They've either stopped making them or they're hiding them really, really well. :)

hrm, poking around, i found the eg651p isn't sli certified. the EG565P-VE FMA, however, is (according to nvidia's site). and it's super cheap. nothing but good reviews so far on it. runs dual 12v@18a, which is plenty for my planned config. seems too good to be true.

(i should get an award for most edited posts): going to the store today, and i'm gonna give the enermax liberty 500W a whirl in my current box. once i go SLI,. which won't be for a good, long while, if the 500W liberty doesn't handle it, i'll have enough $$$ for a better PSU as well as the extra video card. if i'm unsatisfied with the liberty's modular design, i'll return it and get the EG565P-VE FMA. and see if that makes me happy. i have a feeling, though, that the liberty will be fine now, and fine when i go sli. if i could get the 620W, i would, but eh, i just can't justify the cost. and maybe the 500W will give me a bit overhead on my current setup to up some voltages and get some good clocks to hold me over until i get all the components for my new rig. (double posting this edit, since i have two similar threads going on my build - please forgive)
 
The EG651P must be discontinued. Lots of hits on google. The one I use, the EG851AX, is an EPS12V unit with the 8-pin mb connector for dual procs, but comes with an adapter for 4 pins, which I'm using on the Asus A8N32-SLI. The case is made of aluminum, and it has 2 80mm fans. I was surprised at how quiet it is. A bit expensive though.

http://www.enermax.com/english/product_Display1.asp?PrID=37
 
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