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baldbrad
11-18-06, 09:43 PM
hello all,one simple question.I'm getting a 8800gts(have a 9600xt right now,cant wait:captnkill: )i read that the power req for the card is a 12v rail at 26a.

I can tell ya right now,that when it comes to volt,amps i am completly lost.

So i looked at my PSU,it is a turbolink 500w,these are the specs on the side.

3.3v...5v...12/1v...12/2v
---------------------------
17a...25a...16a.....18a


If im reading it right my PSU will not work?If any one can confirm it will/wont work that would be great,thank you

SlieTheSecond
11-18-06, 09:48 PM
What you need is a combined total of 26A on the 12V rails.
You have a combined total of 34A.

You should be fine unless you has a zillion other things in your computer drawing power.

baldbrad
11-18-06, 11:40 PM
Phew,ok i see how to do that now.

Thank god,a new PSU wouldnt have fit into my budget.

Xion X2
11-19-06, 12:26 AM
What you need is a combined total of 26A on the 12V rails.
You have a combined total of 34A.

You should be fine unless you has a zillion other things in your computer drawing power.

Where are you guys getting this from? Dual-rail PSU's don't abide by the same rules as you're stating.

The processor takes up the entire first 12v rail on dual-rail PSU's all to itself, therefore you only have available amps on 12v2 to run your graphics card.

ManOnFire
11-19-06, 04:06 AM
8800 GTS works fine on my Fortron 400W psu:

12V1 = 14A
12V2 = 15A

It worked fine on my 7800GT SLI also. The quality and ATX version of the psu is a big factor, make sure it is a ATX 12V ver2.01 or higher. I wouldnt try a 8800 GTX or 8800 GTS SLI on my 400W though.

technoid
11-19-06, 08:08 AM
I think of it this way. Each additional power connector on a PCI Express graphics board is suppose to supply an additional 75 Watts of power. So if you put the graphics board on a Dedicated 12v Rail all you should need is 75 / 12 or 6.25 Amps from that rail. Of course I'd give that some headroom.

This assumes you have a quality power supply. Those 35 dollar cases with 400 watt power supplies should be thrown away.

SlieTheSecond
11-19-06, 12:06 PM
Where are you guys getting this from? Dual-rail PSU's don't abide by the same rules as you're stating.

The processor takes up the entire first 12v rail on dual-rail PSU's all to itself, therefore you only have available amps on 12v2 to run your graphics card.

Hmm it says that on my 8800 GTS box. All you need is a combined total of 26A to run the card.
Plus my old psu with a single 12V of 30A seem to run it fine too.

He has a 12V combined of 34A. So naturally, one would assume it is enough.

SH0DAN
11-19-06, 12:48 PM
http://www.hardforum.com/showthread.php?t=974240

Xion X2
11-19-06, 03:17 PM
Hmm it says that on my 8800 GTS box. All you need is a combined total of 26A to run the card.

That is as long as you actually HAVE 26A to feed the card with. And what I'm trying to say is that on that dual-rail PSU the original poster has, he doesn't. What he has is 16A on rail one that can feed nothing but his processor.

On dual-rail PSU's, you cannot distribute amps on 12v1 to anything but the processor. So those 16A cannot be included in a vague statement about needing "26A" total to run a GTS off of.

Plus my old psu with a single 12V of 30A seem to run it fine too.

That is because all of those amps were available to pull from, whereas they are not on a dual-rail PSU. Single 12v rail PSU's do not hog 16A for the processor alone like the dual-rail that this individual owns does. They dedicate whatever is needed and allow the rest of the system components to pull from the rest. This is quite a difference and should be taken into serious consideration when discussing the issue.

Nvidia just doesn't put it on their vendors' boxes because it gets so damn confusing. It's just not a cut and dry issue, unfortunately.

baldbrad
11-19-06, 03:59 PM
HMMMMM.....ok i can just end the debate if my psu is good enough or not by just getting a high end one:)

Now......like i stated PSU's,amp's,volt's,rails,dual rails,could be french to me,i just dont understand it:)so with that said,i can sweet talk the wife for another 100-150 bucks,so can any one recommend one for me?I will not be going SLI,i will be overclocking some.componets are as follow e6400,Corsair DDR2-800 XMS2-6400,dvd burner,250gb sata hd,8800gts,giga ds3 mobo.

Thanks for helping the noob out:)

baldbrad
11-19-06, 04:11 PM
ok,did a little reading and i think that a Seasonic m12 500 would do fine in my system,i like the modular wires and how they are sleeved.

Any thoughts?

Xion X2
11-19-06, 04:21 PM
Seasonics are excellent power-supplies. You can't go wrong with a Seasonic, Silverstone, or PCPower & Cooling--just make sure that it doesn't have dual 12v rails. If it's single, tri, or quad, then you're in good shape. But do not buy a dual-rail power-supply.

darrenj
11-19-06, 04:26 PM
**** how about my Levicom 550w? I am worried

check specs here!

http://www.nordichardware.com/Reviews/?skrivelse=365&page=7

SlieTheSecond
11-19-06, 04:38 PM
That is because all of those amps were available to pull from, whereas they are not on a dual-rail PSU. Single 12v rail PSU's do not hog 16A for the processor alone like the dual-rail that this individual owns does. They dedicate whatever is needed and allow the rest of the system components to pull from the rest. This is quite a difference and should be taken into serious consideration when discussing the issue.

Nvidia just doesn't put it on their vendors' boxes because it gets so damn confusing. It's just not a cut and dry issue, unfortunately.

I stand corrected. I was unaware that with a dual rail psu, one rail is dedicated to the cpu.

That brings up a new question tho. Why is it that way with dual rail, if 1,3,4 rail it is not?

Xion X2
11-19-06, 04:59 PM
I stand corrected. I was unaware that with a dual rail psu, one rail is dedicated to the cpu.

That's okay; you're not the only one. I was once of the same mindset before I did further research into the subject.

That brings up a new question tho. Why is it that way with dual rail, if 1,3,4 rail it is not?

Well, it's actually only different on single-rail models. Single-rail models are able to balance the load of amps across all components. Allow me to offer an example:

Say you have a processor that consumes 9A on average (I don't know what they actually consume off the top of my head, but I'm willing to wager that this is close), and you have the Silverstone ST56ZF 560W PSU that has a single 12v rail rated @ 38A. That allows you 29A for the rest of your components to pull from--and this is further balanced if you have a processor that takes up less than 9A. The system is allowed to pull even more if starved for power and the amps are there to pull from.

Unfortunately, this isn't the case w/ dual-rail models. Dual-rail models need to balance the power-draw between rails, and up until recently ATX specs allowed no more than 20A per 12v rail. So, since the design of dual-rail PSU's necessitates that the CPU have its own dedicated rail (to assure that the system will always be able to run at the most basic level), you are always goign to have overkill power on rail #1 as opposed to rail #2 which will actually run most of your components. You cannot balance the excess amps off rail #1 onto rail #2. This is a common example of why dual-rail PSU's are poorly designed and poorly optimized for high-end performance, and is the primary reason they are being phased out in the power-supply industry while companies begin to expand into tri and quad-rail specifications.

But something that is important to understand is that tri and quad-rail models actually have to abide by the same rules as dual-rail PSU's. The processor has its own dedicated 12v rail, which is usually 12v1. The difference, however, lies in the fact that tri and quad-rail models do not force you to run everything but your processor off a single 12v rail. In the case of a tri-rail PSU, you now have TWO rails to pull from, instead of just one like you do on a dual-rail PSU. And in the case of quad rail models, you have three. And in the case of five 12v rail models, like the Enermax Galaxy 850/1000W'ers, you have four.

Make sense?

ManOnFire
11-20-06, 02:43 AM
Lets say

12V1: 14A*12V=168W for the cpu
12V2: 15A*12V=180W for other 12V components
+5V: pci-e, other mobo components (correct me if im wrong here)

The 8800 GTS pulls about <=150W at max if im correct, 75W of those from the pci-e connector which i assume get its power from +5V.

So the 8800 GTS will pull at most 75W from 12V2 leaving 105W (8.75A) for cd/dvd/hard -drives and other 12V components. This seems like a good rail power distribution-balance to me.

shaker718
11-20-06, 08:54 PM
I talked to the guys at www.Jonnyguru.com and they recommended (for my budget) the Modular Enermax liberty 500w ( which is what I have now) 22a on the 12v1 and 22a on the 12v2. It's SLI ready and so far has been rock solid. for about 100 bucks its a pretty sweet PSU and quiet. Only thing I didn't like about it where the dual sata- molex cords but they ended up being handy since I plugged my 2 SATA drives and the case fans on one cable, makes everything super tidy.

oh and one more complaint: My old Antec truepower 430 had a case fan specific cable that made the fans run faster or slower depending on temperature. It made my system super silent until I started gaming. Right now those fans are running full tilt and they are loud.


On the upside it's a good way to justify getting an Antec P180b case on friday:D

ManOnFire
11-26-06, 03:59 AM
I found this article on single/dual -rail psu's:

http://www.xbitlabs.com/articles/other/display/atx-psu5.html

The short version is that dual-rail psu's really are single-rail where they have maximized the power output per lead. 12V1 and 12V2 is max output on lead 1 and 2. So 14A+15A really is 29A.

Redeemed
11-26-06, 04:06 AM
I was able to run a single 8800GTS on my TTGI 550watt PSU which only had 30 Amps on the 12v rail (it was a single rail PSU).

Just don't try running two of 'em on that PSU. It'll kill it in a heart beat (trust me, I learned that the hard way).