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Multiple 12v rails?

post #1 of 19
Thread Starter 
Hi all.

I wanted to buy an nVidia 6800GT to upgrade a friend's computer (He now has a FX5700 Ultra).
Anyway, on the internet I read that this video card needs at least 18A on the +12V rail to run at full performance.
I just checked the computer's PSU and here are it's specs:

Antec Basiq Power 350W (BP350P)
And this confused me, because i'm new to the world of PSU's:
+12V1: 10A
+12V2: 13A

Does this mean it has 23A (and i can safely use the card)?
Or does it mean that I have only 13A (and cannot use the card)?

Thanks,
xIntenso
post #2 of 19
It has 23A on the +12v. The 6800GT should work fine.
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post #3 of 19
You typically can't add up rails like that. PSUs with multiple 12V rails should clearly state what the maximum output is on all the +12V rails combined. The info will be on the PSU's sticker. In the case of the BP350P, the sticker says this under the power distribution table: +12V1, +12V2 max. load: 276W, which is 23A. So in this case, it matches the result when you add 10 and 13 together, but it often doesn't, so you need to look for that mention.
post #4 of 19
Thread Starter 
Quote:
Originally Posted by GameBoy View Post
It has 23A on the +12v. The 6800GT should work fine.
Yay
Thanks a lot!
post #5 of 19
Thread Starter 
Quote:
Originally Posted by Shub View Post
You typically can't add up rails like that. PSUs with multiple 12V rails should clearly state what the maximum output is on all the +12V rails combined. The info will be on the PSU's sticker. In the case of the BP350P, the sticker says this under the power distribution table: +12V1, +12V2 max. load: 276W, which is 23A. So in this case, it matches the result when you add 10 and 13 together, but it often doesn't, so you need to look for that mention.
As in I = P/U
I = 276W/12V = 23A?

Edit: Oh, and Rep+ to both of you.
post #6 of 19
Just to know... Why would you call a 7 years old card an upgrade?
I mean, for even 250$ you could certainly get something way better. And I mean 250$ for a whole PC, not a gpu
Edited by SHNS0 - 3/21/11 at 8:27am
     
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post #7 of 19
Quote:
Originally Posted by xIntenso View Post
As in I = P/U
I = 276W/12V = 23A?
Correct
post #8 of 19
Quote:
It has 23A on the +12v. The 6800GT should work fine.
Edit: Sorry mate but it doesn't work like that. It can be done, but you don't just add up rails like that. If he pulls 18A from a single 13A rail, it doesn't matter the second rail has 10A available, the PSU will be overloaded.

_____________
First of all, 18A seems excessive, this is over 200W worth of power and the 6800 is nowhere near that value (maybe 13A - 150W).

Power delivery is like water pressure, here's an analogy: say you need 18gallons/second of water in a tank. You have two pipes, each providing a max of 13gl/s and 10gl/s. Both of them could supply the necesary 18, but taken individually neither can.

I suppose he also powers the processor and all the rig from this PSU, so the 10+13amps may not be all available. The manual of the PSU (probably you can find one online) says which connector is powered by which rail. The ATX connector probably takes 2A from a rail, the CPU some 4-6A (if not OCed, more if OCed) from the same or another rail, disks some 1-2A in total. You're still left with some 13A available which should be enough.
To pull those 13W I advise you to get an adapter that connects on two male connectors !one for each rail! and has one male PCIe connector to plug into the graphics card. It's a pretty complicated setup, but it should be doable.
...alternatively he could try finding a graphics card that doesn't need a 6-pin PCIe connector (5670/5570 DDR5 should be better than a 6800) or buy a PSU with a single beefier +12V rail.
Edited by dragosmp - 3/21/11 at 8:28am
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post #9 of 19
It should work.
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post #10 of 19
Quote:
Originally Posted by SHNS0 View Post
Just to know... Why would you call a 7 years old card an upgrade?
I mean, for even 250$ you could certainly get something way better. And I mean 240$ for a whole PC, not a gpu
It's an AGP card...
    
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