Using two 7950s

[EfficientSystems]

You should consider the smaller asic systems hitting the market. The USB plugs are a thing of beauty for replacing your video cards and I would suggest those. If you haven't gotten one soon then the group I represent will be making an offering on the market as well that you can consider.

[suprabitz]

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%).

You also gotta realize the rated wattage is AT THE WALL. If you have a 70% efficient power supply you only have 385w to the components, and your 7950 will be pulling 200+ watts, your P4 is a power hog. You're already at 400 watts with the 2 7950's so you're over capacity. Then if you have a HD, CDROM, PCI cards, etc you are WAY over capacity. I'm surprised it ran at all. You can get a Thermaltake 750w bronze power supply on sale at newegg for $50 with rebates, or I just got an OCZ 850w modular Gold for $85 w/rebates and you will not only have a higher rating but greater efficiency

[zackclark70]

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%).

You also gotta realize the rated wattage is AT THE WALL. If you have a 70% efficient power supply you only have 385w to the components, and your 7950 will be pulling 200+ watts, your P4 is a power hog. You're already at 400 watts with the 2 7950's so you're over capacity. Then if you have a HD, CDROM, PCI cards, etc you are WAY over capacity. I'm surprised it ran at all. You can get a Thermaltake 750w bronze power supply on sale at newegg for $50 with rebates, or I just got an OCZ 850w modular Gold for $85 w/rebates and you will not only have a higher rating but greater efficiency

the rated power should be the output power so a 90% 1000w psu could pull up to 1100w from the wall

[atariguy]

You should consider the smaller asic systems hitting the market. The USB plugs are a thing of beauty for replacing your video cards and I would suggest those. If you haven't gotten one soon then the group I represent will be making an offering on the market as well that you can consider.

I looked at those, but when you can spend the same amount on a GPU with a much better hash rate, it doesn't really seem worth it (even when energy is considered).

[atariguy]

You also gotta realize the rated wattage is AT THE WALL. If you have a 70% efficient power supply you only have 385w to the components, and your 7950 will be pulling 200+ watts, your P4 is a power hog. You're already at 400 watts with the 2 7950's so you're over capacity. Then if you have a HD, CDROM, PCI cards, etc you are WAY over capacity. I'm surprised it ran at all. You can get a Thermaltake 750w bronze power supply on sale at newegg for $50 with rebates, or I just got an OCZ 850w modular Gold for $85 w/rebates and you will not only have a higher rating but greater efficiency

I disconnected everything I wasn't using to minimize power demands. It's running right now on a borrowed 750w power supply. I haven't yet tried the 700w (it came yesterday), but with the 750 it runs fine all day but then crashes each night and has to be powered down for a few minutes. I haven't yet investigated the cause of the crash, but I suspect it might be the 5+ year old hard drive I'm using.

[zackclark70]

You also gotta realize the rated wattage is AT THE WALL. If you have a 70% efficient power supply you only have 385w to the components, and your 7950 will be pulling 200+ watts, your P4 is a power hog. You're already at 400 watts with the 2 7950's so you're over capacity. Then if you have a HD, CDROM, PCI cards, etc you are WAY over capacity. I'm surprised it ran at all. You can get a Thermaltake 750w bronze power supply on sale at newegg for $50 with rebates, or I just got an OCZ 850w modular Gold for $85 w/rebates and you will not only have a higher rating but greater efficiency

I disconnected everything I wasn't using to minimize power demands. It's running right now on a borrowed 750w power supply. I haven't yet tried the 700w (it came yesterday), but with the 750 it runs fine all day but then crashes each night and has to be powered down for a few minutes. I haven't yet investigated the cause of the crash, but I suspect it might be the 5+ year old hard drive I'm using.

i had that problem on 1 of my rigs look on gpu z and see what voltage the carge core voltage is ( if you are using adapters the voltage will sag a small amount i had to up the voltage 0.002v

[SirMintALot]

I disconnected everything I wasn't using to minimize power demands. It's running right now on a borrowed 750w power supply. I haven't yet tried the 700w (it came yesterday), but with the 750 it runs fine all day but then crashes each night and has to be powered down for a few minutes. I haven't yet investigated the cause of the crash, but I suspect it might be the 5+ year old hard drive I'm using.

Probably the cards heat up to much and cause the crash. Try to optimize your airflow, adding an extra fan might help.

[atariguy]

It looks like it might have been the power supply I was using. I hooked up my new 700w PSU on Sunday, and it's been stable (so far) ever since. Here is a pic of my setup (please pardon the mess):

https://www.box.com/s/iasm3kbvorxyhphxa6hj

Other than adding an external fan (which I'm not sure is necessary at this point), there's not much that can be done to optimize airflow - you'll see my 2nd GPU is actually sitting out in the open, on top of the case!

(edit: fixed the pic so it doesn't contain my address...)

[Digi128pci]

I only buy premium psu's like corsair, OCZ, ... the cheapones didn't last long even when they supposed to be more powerfull.
What you should look at is one 12V line, the GPU cards use the 12V line for power. if you have once common 12V line you use it more efficient.
example: 2 x12V line , 2 x300w , you're card 2 x 280w, 20w reserve at each line can cause trouble.
If you have 1 common 12V line 1 x 600w, 2 x280w gpu, 40w reserve witch can work.

[atariguy]

Thanks again for the replies. It's now been running stably for 5 days, so I guess I made a good choice! 

[Amph]

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.

nah the ax750 gold series or platinum, will do the trick easily

[Xanthe]

Thanks again for the replies. It's now been running stably for 5 days, so I guess I made a good choice! 

That's very good to hear! Congrats on getting things running smoothly.

[mirek]

It is nice read as I can consider same setup  and now I know optimal PSU power from the story.
Thanks a lot.

[atariguy]

I just received a Kill-a-Watt in the mail last night, and hooked it up to see how many watts this thing is actually sucking. It averaged around 640 for the time I had it connected, sometimes actually going above 700 (my PSU is rated for 700). The weird thing is, it had been running steady for nearly 2 weeks, but it had trouble keeping up the hashrate while plugged in to the Kill-a-Watt. After I removed the Kill-a-Watt, it went back to running normal again.

Without cgminer running, it actually uses twice as much as my main PC (with an i7 CPU) playing Tomb Raider with a 7770 GPU. I guess a P4 CPU probably isn't the most efficient choice for a mining rig...but it was free.