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#1
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8800 GTS
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 |
#2
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8800 GTS
stiffman320 wrote:
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/vid...gts-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.co...0425e36416dd39 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 |
#3
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8800 GTS
In message Paul wrote:
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? -- If quitters never win, and winners never quit, what fool came up with, "Quit while you're ahead"? |
#4
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8800 GTS
DevilsPGD wrote:
In message Paul wrote: 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? We're talking about the 12V DC output of the power supply. 12V * 19A is 228W, just a few light bulbs worth :-) Paul |
#5
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8800 GTS
In message Paul wrote:
DevilsPGD wrote: 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 :-) Ahh, for some reason I assumed the 20amps was converted back to 120V for purposes of this discussion. -- If quitters never win, and winners never quit, what fool came up with, "Quit while you're ahead"? |
#6
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8800 GTS
"DevilsPGD" wrote in message ... In message Paul wrote: DevilsPGD wrote: 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 :-) Ahh, for some reason I assumed the 20amps was converted back to 120V for purposes of this discussion. -- If quitters never win, and winners never quit, what fool came up with, "Quit while you're ahead"? 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. |
#7
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8800 GTS
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! |
#8
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8800 GTS
Wait a minute. Can the 8800 (or any GPU card as a matter of fact) be
wired to draw power from two different rails? |
#9
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8800 GTS
stiffman320 wrote:
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...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...00gts_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/asse...5Q_copper2.jpg Paul |
#10
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8800 GTS
On Jun 10, 2:07 am, DevilsPGD wrote:
In message Paul wrote: 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? 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. |
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