How to use two HD 6970 + HD 6970 with 850W PSU?

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eurgbp

Member
May 2, 2013
27
0
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MS-Tech 850W PSU MS N850VAL 12cm Ver. 2.3 retail
Rail one is 12V1 max 324 Watt, 28 Ampers
Rail two is 12V2 max 324 Watt, 28 Ampers
PSU has one 6 pin PCIE cable and one 8(6+2) pin PCIE cable
Several SATAs + several Molex
One 6970 takes ~370 Watt fully loaded and idle state takes ~120 Watt
Can I install second GPU 6970?
Where are first and second rails?
What amper load is currently on first and second rail?
How to evenly distribute Amps current load between two rails?
Should I use sata to 6 pin pcie converter cable and molex to 8 pin pcie converter cable to feed second 6970 GPU?
I am so confused right now…
 
TakeNoPrisoners

TakeNoPrisoners

Platinum Member
Jun 3, 2011
2,600
1
81
That PSU has two PCI-E connections. A decent quality unit of that magnitude should have about four. My guess is that PSU only puts out about 400w on a good day.
 
Last edited:
toyota

toyota

Lifer
Apr 15, 2001
12,957
1
0
eurgbp said:
why not?
28A+28A should be enough for two 6970?
Click to expand...
noob mistake adding two rails together. and as others have mentioned that is clearly not a very capable "850 watt" psu if it only came with two pci-e connectors.
 
3

3DVagabond

Lifer
Aug 10, 2009
11,951
204
106
Looked at the specs. The unit is not 80+ certified. So, there's no way to verify the rating. It's rated at 850W max. You want to know what it's continuous rating is, but they don't give it.

The likely way they got the rating is that's where the OCP (over current protection) circuitry is set to trip. If you add those specs up it comes to ~850W. Nothing at all to do with it's actual output.

Just as an example, if you were to take an Antec 850W and rate it the same way it would be a ~2150W unit. :\
 
S

Smoblikat

Diamond Member
Nov 19, 2011
5,184
107
106
eurgbp said:
why not?
28A+28A should be enough for two 6970?
Click to expand...

Its not the max theoretical output thats the issue, its the fact that that is a low quality unit that I wouldnt trust to run anything other than a P4 and an 8400GS.
 
Stuka87

Stuka87

Diamond Member
Dec 10, 2010
6,240
2,559
136
It should be noted you don't have to spend $200 to get a decent 850W PSU to do what you want. The Antec listed above is a very good supply, but there are some 80+ certified that are quite a bit less. Gold certified PSU's always sell for a premium.
 
S

Smoblikat

Diamond Member
Nov 19, 2011
5,184
107
106
Stuka87 said:
It should be noted you don't have to spend $200 to get a decent 850W PSU to do what you want. The Antec listed above is a very good supply, but there are some 80+ certified that are quite a bit less. Gold certified PSU's always sell for a premium.
Click to expand...

I have a 1300W platinum rated one and it cost me 225$. I wouldnt spend more than 140$ on an 850W PSU, and it better be damn good for that price.
 
S

Smoblikat

Diamond Member
Nov 19, 2011
5,184
107
106
Zargon said:
no OC at all....maybe


I had a nice XFX650W 80plusBronze that wouldnt boot 2x6950's and an OC'd 2500K with 8gb of ram
Click to expand...

Used to run a GTX 470 + GTX 275 (HEAVY OC) plus a Phenom 2 X4 @ 4ghz on that PSU..............
 
Shmee

Shmee

Memory & Storage, Graphics Cards Mod Elite Member
Super Moderator
Sep 13, 2008
7,409
2,441
146
Since this is more of a PSU question, I am moving it to Power supplies.
 
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