8800 GTS


S

stiffman320

Thanks for your guys' help on my other post. Especially the part about
being twice as likely to have problems. I already have one.

The 8800 says it requires 26amps on the 12V+ rail.
Where do I get a PSU like that? The couple that I did find were $200+
and had over 800W.
Do I really need that much power? Or does a 600W PSU with 19amps do
the job?
If it sounds to you like I have no clue about power supplies or amps,
it's because I don't
 
Ad

Advertisements

P

Paul

stiffman320 said:
Thanks for your guys' help on my other post. Especially the part about
being twice as likely to have problems. I already have one.

The 8800 says it requires 26amps on the 12V+ rail.
Where do I get a PSU like that? The couple that I did find were $200+
and had over 800W.
Do I really need that much power? Or does a 600W PSU with 19amps do
the job?
If it sounds to you like I have no clue about power supplies or amps,
it's because I don't
Working out the power supply size, is like being an accountant.
You have to add up all the little bits, to get the overall picture.

The estimates provided by the video card makers, tend to be on the
high side. So you can survive with less, but how much less depends on
your system.

For example, a Core2 Duo might draw 6 amps from the 12V rail. A
previous generation, high end Pentium 4 might draw 130W, which
is roughly 12A from the 12V rail, at 90% Vcore conversion efficiency.
So if the video card company thinks about the Pentium 4 case, while
you are using a Core2 Duo, then they include 6A too much right there.

If you are planning on overclocking the processor, then the Core2 Duo
will draw proportionally more power, so that too must be taken into
account. That was particularly serious, for people overclocking D 805
dual core processors, because you could draw close to 200W if severely
overclocking one of those. Multiply the 6A Core2 Duo number, by the
percentage overclock, as a rough estimate.

So it does require some attention to details, to get the right answer.
There is a big difference, between a person using one hard drive and
someone using a dozen hard drives.

Numbers for the 8800 family are here, near the bottom:

http://www.xbitlabs.com/articles/video/display/msi8800gts-640_6.html

When you can post the expected set of components you will be using,
then it may be possible to work out an estimate.

Post #9 here, is an estimate for a Core2 system with an 8800 family
card. Total current is estimated at 13.2A + 6A from the two 12V
rails. Post #12 is with a slight component change to the config.

http://groups.google.ca/group/alt.comp.periphs.videocards.nvidia/browse_frm/thread/97dcdddeeeffbdf1/e00425e36416dd39

So 20 amps total appears to be enough for a basic Core2 Duo system,
without provision for overclocking. I also like to see a little
margin, over and above the calculated number, so 19A doesn't sound
like enough. The split between rails can also be important, but it
sounds like your old supply is a single rail unit.

If you want more details, a make/model of the power supply, and
a URL to the product web page, would help. As would any details
of the hardware you plan to use.

HTH,
Paul
 
D

DevilsPGD

In message said:
So 20 amps total appears to be enough for a basic Core2 Duo system,
without provision for overclocking. I also like to see a little
margin, over and above the calculated number, so 19A doesn't sound
like enough. The split between rails can also be important, but it
sounds like your old supply is a single rail unit.
19A sounds high for a PC, given that most household circuits are only
rated for 15A-20A. What am I missing here?
 
P

Paul

DevilsPGD said:
19A sounds high for a PC, given that most household circuits are only
rated for 15A-20A. What am I missing here?
We're talking about the 12V DC output of the power supply.
12V * 19A is 228W, just a few light bulbs worth :)

Paul
 
D

DevilsPGD

In message said:
We're talking about the 12V DC output of the power supply.
12V * 19A is 228W, just a few light bulbs worth :)
Ahh, for some reason I assumed the 20amps was converted back to 120V for
purposes of this discussion.
 
M

Michael Hawes

DevilsPGD said:
Ahh, for some reason I assumed the 20amps was converted back to 120V for
purposes of this discussion.
Yes 8800GTS needs the combined 12V rail(s) to be 26A, or it will fail to
work at full speed (or even at all). The 8800 needs about 100W itself!

Mike.
 
Ad

Advertisements

S

stiffman320

Ok, that helps a bunch!
I found a PSU with 2 12V rails, one with 19A and the other with 18A.
Should run my system no problem.

I'd have to buy another PSU if I plan to upgrade SLI in the future
though.

Anyway, thanks!
 
S

stiffman320

Wait a minute. Can the 8800 (or any GPU card as a matter of fact) be
wired to draw power from two different rails?
 
P

Paul

stiffman320 said:
Wait a minute. Can the 8800 (or any GPU card as a matter of fact) be
wired to draw power from two different rails?
The 8800GTS has one PCI Express 2x3 power connector. The 12V on there
comes from 12V1.

12V2 powers the processor and only the processor. Check this 24 pin power
supply spec, to see how the thing is wired.

http://www.formfactors.org/developer/specs/ATX12V_PSDG_2_2_public_br2.pdf

If you had a Core2 Duo, for example, 12V2 would give 6A to the processor
and the rest of the capacity on that output would not necessarily be
used. The rest of the power, whether it is 13.2 amps or some higher number,
would come from 12V1.

The 8800GTS would use some 12V1 flowing through the main connector (3.5A),
and some 12V1 (6A) flowing through the 2x3 on the end of the card.

http://www.xbitlabs.com/images/video/msi8800gts-640/nx8800gts_full.gif

If buying a power supply, not only should you check the power numbers,
but you also want the proper connectors on the end. For example, if you
were doing a dual 8800GTX, you'd want a supply with four 2x3 PCI Express
connectors on it.

This is an example of a power supply that is ready for just about
anything. It even has an option for the new 2x4 that will be used
soon on some power hungry video cards.

http://www.pcpower.com/products/assets/S75QB/S75Q_copper2.jpg

Paul
 
D

Dean G.

19A sounds high for a PC, given that most household circuits are only
rated for 15A-20A. What am I missing here?
15A @ 110 (or 120 if you feel lucky) = 1650 watts (or 1800 watts, and
keep a few extra fuses and a fire extinguisher handy).

19A @ 12V = 228 watts.

The voltage stepping occurs inside the power supply, so the houshold
fuse is only feeling about 2 amps of current.

Dean G.
 
D

Dean G.

Yes 8800GTS needs the combined 12V rail(s) to be 26A, or it will fail to
work at full speed (or even at all). The 8800 needs about 100W itself!
The 100 watts I believe (maybe even a bit more "peak" power, but not
average). I call bullshit on the 26A @ 12V, which is 312 watts. I have
an 8800GTS, and it does not draw 312 watts of power even under heavy
use.

Dean G.
 
Ad

Advertisements

M

Michael Hawes

Dean G. said:
The 100 watts I believe (maybe even a bit more "peak" power, but not
average). I call bullshit on the 26A @ 12V, which is 312 watts. I have
an 8800GTS, and it does not draw 312 watts of power even under heavy
use.

Dean G.
The 26A refers to TOTAL 12V supply, not just the 8800.

Mike.
 
Ad

Advertisements

E

Ed Medlin

Great power supply. I wouldn't buy anything less.
I have thePC P&C 750 SLI and it is great. Only one 12v rail powers all that.
I have two 8800GTX cards in SLI and all four power plugs are provided. Great
PSU.


Ed
 

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments. After that, you can post your question and our members will help you out.

Ask a Question

Top