Using two 7950s

[atariguy]

I've been using a rather old P4 system with a 7950 card for mining, and decided to add another one. I have a Coolermaster 550W PSU. I added in the 2nd card last night, and was pleasantly surprised to see cgminer pick it right up and go, using the same settings as it used for the first one. However, once the fans on both GPUs got going, the system froze.

I decided I must be drawing too much power, and set the shutoff temp to 75 instead of 85. That did the trick, and I let it run overnight. This morning, I noticed a smell that can only be detected from a distance - if you put your nose right up to the GPUs or the PSU you can't smell anything. I pulled the new GPU out for the day and went to work, so I wouldn't worry about it all day.

I decided I probably need a better power supply, so I ordered this one that New Egg has on a 48 hour sale:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817171037&nm_mc=EMC-IGNEFL060413&cm_mmc=EMC-IGNEFL060413-_-EMC-060413-Index-_-PowerSupplies-_-17171037-L013C

My questions are, is this power supply going to be powerful enough, and is the smell related to the power supply I'm currently using? (I do know at least that my current one probably isn't powerful enough since the system froze when the fans got going at 100%).

[Kaepora]

I've been using a rather old P4 system with a 7950 card for mining, and decided to add another one. I have a Coolermaster 550W PSU. I added in the 2nd card last night, and was pleasantly surprised to see cgminer pick it right up and go, using the same settings as it used for the first one. However, once the fans on both GPUs got going, the system froze.

I decided I must be drawing too much power, and set the shutoff temp to 75 instead of 85. That did the trick, and I let it run overnight. This morning, I noticed a smell that can only be detected from a distance - if you put your nose right up to the GPUs or the PSU you can't smell anything. I pulled the new GPU out for the day and went to work, so I wouldn't worry about it all day.

I decided I probably need a better power supply, so I ordered this one that New Egg has on a 48 hour sale:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817171037&nm_mc=EMC-IGNEFL060413&cm_mmc=EMC-IGNEFL060413-_-EMC-060413-Index-_-PowerSupplies-_-17171037-L013C

My questions are, is this power supply going to be powerful enough, and is the smell related to the power supply I'm currently using? (I do know at least that my current one probably isn't powerful enough since the system froze when the fans got going at 100%).

550W is not enough even a 650 would be better each card pulls 200w plus the system probably pulling 150 -200 watts 550 isnt enough. Honestly I would have gotten a 750W instead, but 700W is good enough as long as you don't add a third card.

[abdullahadam]

With two 7950s, 750W would do, but 850W is better.  Remember, you want this to be stable long term.

By the way, that smell, everytime it happened to me, it was my power supply.

[Kaepora]

With two 7950s, 750W would do, but 850W is better.  Remember, you want this to be stable long term.

By the way, that smell, everytime it happened to me, it was my power supply.

TIP: Also guys, dont use the Molex to PCI-EXPRESS adapters the rails are not designed to run a GPU
http://images17.newegg.com/is/image/newegg/12-400-034-TS?$S300$

Electronics are designed to run at a certain wattage and rating so they can also dissipate enough heat to handle a load they are designed for, if your PSU smells like bunring plastic or warm plastic a component is being overloaded.

You can actually run three graphics cards with an 850W power supply, as long as it is a nice high quality power supply with some beefy rails.

[atariguy]

TIP: Also guys, dont use the Molex to PCI-EXPRESS adapters the rails are not designed to run a GPU

So I shouldn't use the adapters that came with my GPUs? 

[gnarl]

TIP: Also guys, dont use the Molex to PCI-EXPRESS adapters the rails are not designed to run a GPU

So I shouldn't use the adapters that came with my GPUs? 

The ones that came with my card worked fine, but I don't use them unless I have to.
If you do use them check them for heat, if they heat up when hashing the wires are too small and may cause problems.

[Xanthe]

TIP: Also guys, dont use the Molex to PCI-EXPRESS adapters the rails are not designed to run a GPU

So I shouldn't use the adapters that came with my GPUs?  

I think Kaepora is referring to the fact that some PSUs have multiple 12V "rails" meaning that they have multiple 12V outputs between which the power supply's rated output is split. What can happen is if you have a PSU with, say, two 18 amp rails and you try to power two 7950s on a single rail, you'll end up overloading that rail. Normally power supply manufacturers will evenly distribute PCIe power connectors across the rails on multi-rail PSUs so that this does not occur. When you use the Molex -> PCIe power adapter, you just have to be conscious of the maximum amperage on the rail to which you're connecting.

I checked out the PSU that you said that you've ordered and I'm pleasantly surprised. It looks like a nice unit for the price. It has a single 50A 12V rail so you should be able to use the Molex -> PCIe adapter that came with your card without worry (just make sure that all connectors are tight before you fire things up). 50A is enough to power two 7950s but I'd still suggest that you undervolt your cards if possible. This will save you some on the power bill and reduce heat output. Also, make sure that your PSU (in addition to your GPUs, of course ) has adequate ventilation.

As for the smell that you detected. It could very well be from your PSU but also keep in mind that new hardware (i.e. the new GPU) often has a bit of a smell when warmed up for the first time. So maybe it was just your new GPU burning off residue from the manufacturing process... hopefully.

Here's a review of the M700W PSU that I found where it was actually tested: http://www.silentpcreview.com/article936-page1.html

[xetsu]

if u just want bang for buck i think 7850's are your best bet. Personally i think all the new Asics out and their affordability has made bitcoin mining with GPU's pretty bad, think even the electricity might cost you more. So unless you have electricity paid for, or just want to mine in the background, it might not be worth it.

Also make sure to use a mining calculator to find out what your expected profit is etc..

[zackclark70]

you should be fine with 2 cards on that psu ( i jave 3 on a hx750 pulling 700w from the wall )

[cale]

please someone tell me what is the speed with two of those cards?

[zackclark70]

please someone tell me what is the speed with two of those cards?

i have 3 7950s on that rig 1050 core 1250 ram 1.050v 630-640kh / card 700w from the wall

[DannyDisco]

I'm using an 850w for 2 7950's... just to be safe...

[r2vape]

I have the ThermalTake 850 Gold running 3x 7950 Gigabytes and one card is using the two molex to PCIe power adapters off separate "rails".  Working fine for 2 weeks now.

[Kaepora]

I have the ThermalTake 850 Gold running 3x 7950 Gigabytes and one card is using the two molex to PCIe power adapters off separate "rails".  Working fine for 2 weeks now.

Well see how long that PSU lasts in the long run. itll probably be okay though as long as its high quality and you dont pull too many amps from the 12v rail.

[zackclark70]

I have the ThermalTake 850 Gold running 3x 7950 Gigabytes and one card is using the two molex to PCIe power adapters off separate "rails".  Working fine for 2 weeks now.

Well see how long that PSU lasts in the long run. itll probably be okay though as long as its high quality and you dont pull too many amps from the 12v rail.

on my test rig it has a hx750 psu with 3 7950s puling 700w from the wall has been going for nearl 3 monts psu output temp is only 40c

[dracula3]

on my test rig it has a hx750 psu with 3 7950s puling 700w from the wall has been going for nearl 3 monts psu output temp is only 40c

Did you overclock the 7950s. 700W from the wall is very good.

[Alexander The Great]

cool stuff wish i had it.

[zackclark70]

on my test rig it has a hx750 psu with 3 7950s puling 700w from the wall has been going for nearl 3 monts psu output temp is only 40c

Did you overclock the 7950s. 700W from the wall is very good.

my cards are 1050 core 1250 mem 1.050v core  using reaper geting 630kh+ per card

[atariguy]

Thanks for all the replies. I borrowed a 750w PSU yesterday to try, and the GPUs are working great with no smell. Hopefully the 700w PSU that should be arriving tomorrow will work just as well. Besides a $40 rebate, I had a code for $20 off, so it will be a terrific deal if it works (about $50).

For the person that asked, I'm getting a little over 1 GH/s with this setup.

[atariguy]

Anybody ever heard of this brand? It seems too cheap to be any good...

http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=7621664&SRCCODE=LINKSHARE&cm_mmc_o=-ddCjC1bELltzywCjC-d2CjCdwwp&AffiliateID=WxHRncoD05Y-sIkBTH.6BJCONsq1_0dshg

($40 after rebate for 850w PSU)