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Author Topic: Power Supply Question  (Read 3000 times)
stu8
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June 16, 2011, 05:27:21 PM
 #1

Hi!

I`m using the

650W Rasurbo Silent & Power DLP65.1
(only 1x PCIe x6) + adapter from 4p to PCIe x6

for my 5850

I want to add another 5850 but I can only use 2 adapters from 4p to PCIe x6 here. Seems to me that this doesn`t work? Sad

Will for example this power supply be enough?

Sempre BD-700CTP12-E
(2x PCIe x6)

or do I have to buy a

Enermax EPR625AWT II Pro82+
with 4x PCIe x6

??

Thank you!!
stu

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alukardfe
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June 16, 2011, 05:29:40 PM
 #2

 Undecided huh since you will runn this pc all the time buy only a brand psu and go for 80+
and use this to calculate http://extreme.outervision.com/psucalculatorlite.jsp
Bert
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June 16, 2011, 05:40:38 PM
 #3

Each 5850 draws from 151 to 207 watts depending on (over/under)clocking
Call it 170 watts , if not providing some really good cooling.

So for two cards it would draw 340watts allow another 50-100 for CPU/RAM/motherboard/USB/HDD. And allow 90% efficiency for power conversion of PSU.

650W PSU can supply probably 585 watts of power to the computer, the rest is wasted as heat in the conversion from AC to DC.

340+(50 to 100) is 390 to 440 watts and your 650watt PSU can provide 585 watts.

So from my quick back of the envelope calculations there is enough power available all you need is to buy some molex to PCIe converter cables

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stu8
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June 16, 2011, 06:01:40 PM
 #4

thanks guys!

thats what I was expecting... using my rasurbo with one 6pin pcie cable + 3x molex to 6pin pcie adapters

but I can`t get the card running that has only two adapters (deactivated in catalyst)
it seems to work (fan is running) but maybe it has not enough power?!
Bert
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June 16, 2011, 06:07:53 PM
 #5

If you are running windows you will need a second monitor connected to the second card or a cheaper alternative is a fake/dummy/ghost monitor
http://blog.zorinaq.com/?e=11
http://forums.bit-tech.net/showthread.php?t=167450
http://www.soerennielsen.dk/mod/VGAdummy/index_en.php

It worked for someone else that was having issues getting two cards working under windows

If you are running Linux, it just works!

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stu8
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June 16, 2011, 06:13:01 PM
 #6

yep, got a dummy right here.

the problem is... if I connect my monitor with the card that is powered by 2 adapters (and not 1 adapter + the 6pin pcie), I don`t get a signal. so my guess is that there is a problem with the power.
Bert
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June 16, 2011, 06:15:14 PM
 #7

Did you install the driver with the dummy connected ?

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cynikal
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June 16, 2011, 06:16:22 PM
 #8

Undecided huh since you will runn this pc all the time buy only a brand psu and go for 80+
and use this to calculate http://extreme.outervision.com/psucalculatorlite.jsp

cool link.. thanks for that
stu8
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June 16, 2011, 06:18:22 PM
 #9

i installed the driver wenn I got my 1st card.
then equipped the 2nd one + used the adapter.

the 2nd card is exactly the same, should use the drivers from the first one, or what do you mean?!
stu8
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June 16, 2011, 06:19:29 PM
 #10

but since the card that uses the two adapters shows no signal even if it is connected to the monitor, it must be something wrong with the power.

I am using a "gate" like this

http://www.sklep.soft-pc.pl/galerie/a/adapter-molex-molex-fdd_12186.jpg

well.. it comes directly from my PSU but "splits" in two molex. maybe this cable has only power for one pcie adapter but not the two?!
Bert
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June 16, 2011, 06:22:48 PM
 #11

From the 1st link I gave above http://blog.zorinaq.com/?e=11 - "It made sense for drivers to not enable a GPU when no monitor was attached to it. But since the rise of GPGPU applications, graphics vendors AMD and NVIDIA realized that this behavior was inconvenient. At least with the most recent Linux drivers, dummy plugs are not necessary anymore. [Update 2011-02-22: However Windows still requires dummy plugs, as of February 2011.]"

Try downloading whichever of the below are appropriate for your Windows OS. Leave dummy in place, install, reboot, see if the 2nd card is visible.
http://developer.amd.com/sdks/AMDAPPSDK/downloads/Pages/default.aspx AMD-APP-SDK-v2.4-Windows-64 or AMD-APP-SDK-v2.4-Windows-32

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BitcoinBatteries
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June 16, 2011, 06:30:37 PM
 #12

I can speak from experience here.  I just got done putting together a mining computer and used the HD 6970 cards with a 850 Watt Power supply.

I had 3 cards in the computer and and it booted up just fine.  As soon as I turned on the mining it took about 15 seconds for the computer to shut down and that was all she wrote for that power supply, it was dead.  After some head scratching and research I caught on to a very important spec on the power supplies that you want to pay attention to.

The 12 Volt Rails.  Look at how many 12 V rails the power supply has along with the Amperage for each rail.  I ened up getting a 1000 Watt PS with 4 12V rails on it and each rail was 36 Amps.  It runs all 3 6970 cards like a champ but was quite a bit more expensive than the 850 Watt 2 X 12V rails 30 Amp per rail supply that I wanted to use.  The 2 rails at 30 Amp didn't quite cut it for 2 of the 6970 cards.

Hope this helps!
Bert
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June 16, 2011, 06:39:09 PM
 #13

Yea, but 6970 draw from 220 to 360 watts depending on (over/under)clocking and load. Call it 250W with no over/underclocking (it draws 174W when idle).
3 x 250W is 750W and most PSU's are 90% efficent so an 850W PSU can only supply about 765W. Allowing 50-100watts for CPU/RAM/motherboard/HDD/USB and you can see the problem.

EDIT: Sorry I was looking at the wrong graphics card
The 6970 each draw from 323W to 423W, straight away there is an issue trying to power 2+ of them from an 850W (765) PSU.

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stu8
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June 16, 2011, 07:01:11 PM
 #14

Thanks Bert!
I will try out to deinstall my drivers, put my dummy in, restart and reinstall them, just a min.

But still, shouldn`t I get a signal when I turn the pc off, plug the monitor in the 2nd card an start the pc?! Even if it`s not activated in windows, it should show me the bios loading screen etc, right?! (as I said, fan is spinning)
Bert
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June 16, 2011, 07:05:48 PM
 #15

That really depends on the BIOS, the BIOS settings and type of video cable, VGA - probably, DVI - maybe, HDMI - probably not.

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stu8
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June 16, 2011, 07:21:57 PM
 #16

Bert you`re great! Both cards are usable now Wink

But there is another problem now :/ the fan of the 2nd card isn`t spinning or only slow, than stops... any idea?!
Bert
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June 16, 2011, 07:40:27 PM
 #17

Is is being used when it is not spinning ?
Because the fans by default are set to auto, and if the GPU/VRAM/MOSFET's are not being used then the fan will spin down because the temperature will say that there is no need for cooling.

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stu8
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June 16, 2011, 07:42:22 PM
 #18

Was used, yes.

I plugged in the pcie cable for 2nd card, seems to work now (fans for both cards)... don`t why Smiley

Thanks again! Do you know any software that shuts down my pc if the GPU! temp gets to xx?


*edit* the temp was at 99+ so I guess I was pretty lucky that I monitored that right away.
Bert
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June 16, 2011, 07:45:03 PM
 #19

Sorry, under UNIX I could write you a script, but I have no idea under Windows. Hopefully someone else knows the answer.

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stu8
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June 16, 2011, 07:46:32 PM
 #20

Allright! Well, thanks again tho! I will send you something when I made my first btc Wink
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