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How much power for SLI?


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#1
curtwalker

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I'm trying to learn how much power I will need to go SLI in my PC. I'm currently running this graphics card:

http://www.newegg.co...N82E16814130062

If I added a second one for SLI, would something in the range of 500W be enough, or is 600W more realistic? Besides raw wattage, what other specs do I need to consider for the new power supply?

Thanks for your help.
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#2
Titan8990

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Minimum 400 Watt for SLI mode system.
(Minimum recommended power supply with +12 Volt current rating of 24 Amps.)


When it comes to power it is never recommended to cut it close. I recommend getting no less than 550w but 600-650w would probably be best. Other things to consider when getting a PSU is the ammount of amps on the +12v rail. As you can see your set up will require 24a. Any quality SLI certified PSU will have this ammount of amps. Another thing that is important is the effientency rating. I recommend no less that 75% under full load.

Some quality brands to consider:

Antec
Silverstone
Seasonic
Thermaltake
FSP
Mushkin
PC Power and Cooling (very high quality but really too expensive to be practicle)

Antec usually tends to be the cheapest of the quality brands I have listed.
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#3
curtwalker

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Thanks Titan8990. My case is Antec and I had noticed their PSUs getting good reviews on newegg. I also found this one:

http://www.newegg.co...N82E16817182032

If I'm reading it correctly, looks like 35A at the 12V rail and a minimum of 72% or greater. The 550W version is only $5 cheaper so getting the 600W seems like a no-brainer. The 5-eggs reviews also caught my attention.
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#4
Troy

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There's a reason why those Rosewill's are cheap; we really can't vouch for their performance here. You can't go wrong with the list of manufacturer's that Titan8990 gave you.

Try looking at the specifications these ones have, you should be looking more around these:

http://www.newegg.co...N82E16817371002
http://www.newegg.co...N82E16817341010

:)
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#5
curtwalker

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There's a reason why those Rosewill's are cheap; we really can't vouch for their performance here. You can't go wrong with the list of manufacturer's that Titan8990 gave you.

Try looking at the specifications these ones have, you should be looking more around these:

http://www.newegg.co...N82E16817371002
http://www.newegg.co...N82E16817341010

:)


Thanks for the links. I looked through the specs on both of those and I see at least one of them is SLI certified. After scrolling through the specs I couldn't find anything that tells me what amperage applies tot he 12V rails though. Is this a critical issue if the PSU is already SLI certified?
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#6
Titan8990

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Yes, it is. Typically PSUs that are not SLI certified only have one 6pin PCI-E connector as opposed to the two needed for SLI. Both of those PSUs are SLI certified. The Antec doesn't have the little SLI stamp in its picture but if you look in the specifications it is SLI ready. The +12v rails are listed under output in the specifications tab. Here is an example from the Antec:

+3.3@24A,+5V@24A,+12V1@18A,+12V2@18A,+12V3@18A,- 12V@0.8A,+5VSB@3.0A

Edited by Titan8990, 19 October 2007 - 08:07 AM.

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#7
curtwalker

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Yes, it is. Typically PSUs that are not SLI certified only have one 6pin PCI-E connector as opposed to the two needed for SLI. Both of those PSUs are SLI certified. The Antec doesn't have the little SLI stamp in its picture but if you look in the specifications it is SLI ready. The +12v rails are listed under output in the specifications tab. Here is an example from the Antec:

+3.3@24A,+5V@24A,+12V1@18A,+12V2@18A,+12V3@18A,- 12V@0.8A,+5VSB@3.0A


Thanks for your continued feedback. Now, going back to your first reply, you indicated that a PSU that will run an SLI machine needs to provide 24A at the 12V rail. How do I interpret the above string of voltage and amperage values? For example, it says +3.3@24A, and then +12V18A. Does this mean that it only provides 18A at 12V rather than your suggested 24A at 12V?
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#8
Titan8990

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No, the +12v rails on modern power supplies are broken down into multiple rails to more evenly distribute power. This PSU has three +12v rails at 18a each giving it a total of 54a on the +12v rail.
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#9
curtwalker

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No, the +12v rails on modern power supplies are broken down into multiple rails to more evenly distribute power. This PSU has three +12v rails at 18a each giving it a total of 54a on the +12v rail.


Awesome, thanks for clearing that up. I think I'm sufficiently edumacated now on PSUs for SLI. Thanks to all who have giving there feedback.
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#10
Titan8990

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Always glad to help :).
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#11
james_8970

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No, the +12v rails on modern power supplies are broken down into multiple rails to more evenly distribute power. This PSU has three +12v rails at 18a each giving it a total of 54a on the +12v rail.

Just want to note something here, most modern and more advanced PSU's only have one 12V rail, however they have multiple cables to supply the 12V rail. Basically what you are seeing is the maximum amps that can be supplied on each individual cable.
James
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