Question about PSUs and the 8880GT

2007-12-21 21:16:46

#1

aimless: Member; +166|6133|Texas

I was looking at the 8800GT here and at the bottom right it reads:

Minimum of a 400 Watt power supply. (Minimum recommended power supply with +12 Volt current rating of 22 Amp Amps.)

And I was looking at various PSUs on newegg and most of them have +12V rails @ 18A. Is this insufficient? I would assume so. I've looked at almost all the 600-700w PSUs and they all have +12V rails with only 18A.

2007-12-21 21:39:35

#2

claor: Member; +39|6422|Australia

i would ignore that
as far as i know 18 amps is sufficient

2007-12-21 21:54:25

#3

Computer_Guy: Member; +54|6705

Antec
PC Power & Cooling
Corsair
OCZ
FPS

are all good power supply companies. Recomend one of those.
Remeber never skip out on the power supply. It is the heart of your system and if it fails then your whole system fails.

2007-12-22 07:05:55

#4

Bell: Frosties > Cornflakes; +362|6557|UK

+ I wouldnt buy a PSU (or use) that just meets minimum requirements :\ To be on the safe side I tend to add 10% onto recommended requirements just to play safe.

Martyn

2007-12-22 07:13:58

#5

Sydney: 2λчиэλ; +783|6851|Reykjavík, Iceland.

That's 22A if you are talking about a single +12v rail, if you have dual +12v rail 11A on each is sufficient.

2007-12-22 12:20:38

#6

SpIk3y: Minister of Silly Walks; +67|6147|New Jersey

The more +12V rails, the better. And when calculating the amperage, you add all of the +12V rails together. So, if a PSU has 4 +12V rails @ 18A each, it has a total of 72A which is WAY over the minimum. Single +12V rails should be avoided.

This guide explains how all that amperage and rail stuff works. http://forums.bf2s.com/viewtopic.php?id=77096

Last edited by SpIk3y (2007-12-22 12:38:41)

2007-12-22 14:24:39

#7

nukchebi0: Пушкин, наше всё; +387|6332|New Haven, CT

Remember to look at the number of 12v rails, too.

For multiple 12v rail systems, you know how many total amps they can actually provide (which isn't necessarily the sum of each rail) by looking at the total power rated to the 12v rails and dividing it by 12.

Power=volts*amps, thus Power/volts=amps.

For example. The PSU in the guide above has 3 12v rails at 18A each, and a total output of 480W on them. Combined together, 40A can be sent over the 12v rails. I believe the guide is wrong in this case.

2007-12-22 16:17:45

#8

CrazeD: Member; +368|6681|Maine

rdx-fx wrote:
Also, many of the multi-rail systems are not true multi-rail systems - they're cheap crap where there are three rails tied together. So, they end up being more like 18A total for 3 rails.

Sure, if you buy a 50$ POS from Logisys or something.

2007-12-22 16:25:15

#9

r2zoo: Knowledge is power, guard it well; +126|6604|Michigan, USA

SpIk3y wrote:
The more +12V rails, the better. And when calculating the amperage, you add all of the +12V rails together. So, if a PSU has 4 +12V rails @ 18A each, it has a total of 72A which is WAY over the minimum. Single +12V rails should be avoided.

This guide explains how all that amperage and rail stuff works. http://forums.bf2s.com/viewtopic.php?id=77096

Wrong. You dont add the amperage on multiple rails together. It doesnt work that way. Either way you still only have 18a on a 12v rail. Just 4 seperate ones. Only way that would work is if you merged all 4 into a single cable.

2007-12-22 16:28:16

#10

nukchebi0: Пушкин, наше всё; +387|6332|New Haven, CT

r2zoo wrote:
Wrong. You dont add the amperage on multiple rails together. It doesnt work that way.

Yes.

Either way you still only have 18a on a 12v rail. Just 4 seperate ones. Only way that would work is if you merged all 4 into a single cable.

Yes, and you have a certain number overall, which the power supply is capable of providing, found like:

For multiple 12v rail systems, you know how many total amps they can actually provide (which isn't necessarily the sum of each rail) by looking at the total power rated to the 12v rails and dividing it by 12.

Power=volts*amps, thus Power/volts=amps.

For example. The PSU in the guide above has 3 12v rails at 18A each, and a total output of 480W on them. Combined together, 40A can be sent over the 12v rails. I believe the guide is wrong in this case.

Last edited by nukchebi0 (2007-12-22 16:28:36)

2007-12-22 16:28:42

#11

SpIk3y: Minister of Silly Walks; +67|6147|New Jersey

nukchebi0 wrote:
Remember to look at the number of 12v rails, too.

For multiple 12v rail systems, you know how many total amps they can actually provide (which isn't necessarily the sum of each rail) by looking at the total power rated to the 12v rails and dividing it by 12.

Power=volts*amps, thus Power/volts=amps.

For example. The PSU in the guide above has 3 12v rails at 18A each, and a total output of 480W on them. Combined together, 40A can be sent over the 12v rails. I believe the guide is wrong in this case.

I think you're right. I just did some research and according to this Tagan label, your math is the correct way of figuring out the amperage.
http://www.newegg.com/Product/Product.a … 6817814005

Someone should change that guide, because it gave me wrong info It says to add the amps on each rail, which I now see is wrong.

Last edited by SpIk3y (2007-12-22 16:31:29)

2007-12-22 16:29:10

#12

DarkNova: Member; +7|6591

SpIk3y wrote:
The more +12V rails, the better. And when calculating the amperage, you add all of the +12V rails together. So, if a PSU has 4 +12V rails @ 18A each, it has a total of 72A which is WAY over the minimum. Single +12V rails should be avoided.

This guide explains how all that amperage and rail stuff works. http://forums.bf2s.com/viewtopic.php?id=77096

4 +12V rails @ 18A each does not equal to 72A of power. It does not work like that. Total amperage is not the sum of each rail in multi-rail PSU; the actual total amperage will be less than 72A, somewhere around 60 AMPs I think.

2007-12-22 16:55:28

#13

aimless: Member; +166|6133|Texas

wow thanks for all the replies! I'll keep this in mind as I search.

BF2S Forums Question about PSUs and the 8880GT

rdx-fx wrote:

SpIk3y wrote:

r2zoo wrote:

nukchebi0 wrote:

SpIk3y wrote:

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