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I have been seeing threads were people are pushing their PSUs up to their rated power. Some fail and some seem to live a good life (3+ years).

With a bronze rated 80+ PSU would it be too much to push around 93% of its total power? would i get more stales, and or slowly burn out my components do to inefficient power production? I take it that since its 80+ rated and i am not going past 100% of its power rating i am safe... but i figure i should ask the community.

I am looking to build a rig with two 6950s and one 7790 which puts me close to 700w on a spare CMPSU-750TX that i am not selling.

I've been running two 7950s on a 700w PSU. The machine is consuming 675 watts on average. I have a 1200w PSU on order.

Ran mine at at 95% back then. I placed it on the floor on some spacers with the fan pointing down sucking drafty air from just above the floor boards.

Later the noise suppression filter on the AC line burned out, so I bypassed it together with the power switch.

It ran cool the exhaust air didn't feel warm at all.

I literally had to go out yesterday and buy a new powersupply. Kinda in the same boat...heres what happened. I had a wonderful Silverstone 700w that has been chugging along find for over 3 years. All the abuse a 4870x2 and serious overclocking could throw at it. I recently upgraded cpu/mb and got a new 7950...found out about mining and just had to get another 7950. Well...needless to say 700w is right at the threshhold needed to run 2 7950's(recommended is 850+) people say a high quality 750w+ will do the trick.


No such luck for me. Would boot windows fine and even mine for up to 20 minutes but then the system would crash. Went and got a Antec 900w and and cruising at 1.3 gh/s with zero issues.


Moral of the story. DO NOT cheap out on powersupplies. You will limit your production and have nothing but headaches.


zif

It will probably kill a cheap power supply in the short term,

but a good PSU is fine because they're usually rated for more.

See http://www.jonnyguru.com/modules.php?name=NDReviews&op=Review_Cat&recatnum=13

Great, ill give it a try with my Corsair.. ill put a smoke alarm by it just in case :-P

The certifications are for efficiency... Rated power is for output... Consider an 800watt 90+ certified PSU... at 880watts on a 90+ certified psu measured at the wall you'd be putting out: 792watts which is under the rated power of the PSU but just barely.

Honestly you need a kilawatt and you need to look at the amperage on your 12 volt rails. That will tell you what you can run. Test the rig with 1 6970... add another... then add the 7790. You can allways underclock components to bring it into line with your PSU. If you are running this system in a non climate controlled environment or don't like running your AC much in the summer you should also remember that the cards will pull a good extra 20 watts when their fans are running faster this summer.

AndrewK, you arent factoring in efficiencies. Bronze is 82/85/82 efficiency at 20/50/100% loads. So if you have a 800W power supply, then at 100% capacity you will be pulling about 976 watts at the wall (800 / 0.82).

You can safely pull power while being "over spec" at the wall, so long as the actual DC load doesn't exceed the rated amount

..Well, sometimes you can make exceptions, depending on PSU quality. I had a NZXT HALE90 750 watt and I ran it about 10% over spec, something like 950 watts at the wall. It refused to shut off though. Nice power supply :)

.... Ninja edit before actually posting: Never mind, I misread your post AndrewK. You said what I said pretty much :)

go with one of the seasonic OEM models..

Seasonic, XFX and Corsair AX line use these .. they are AMAZING power supplies that are extremely reliable and extremely quiet under high load.

They cost more though...

You are using a CMPSU-750TX. This is a CWT manufactured power supply. Single 60A rail so no concerns there about what card to put where.

The power supply is rated for 50C operation, which is excellent. In fact in testing, they even loaded it to 900W DC (120%!) output: http://www.hardwaresecrets.com/article/Corsair-TX750W-Power-Supply-Review/505/8.

You would likely have no problems running this at 100% load 24/7 in a well-ventilated place.

Capacitor aging WILL accelerate towards higher load. If your PSU lasts 3 years regardless of use or capacity, that's considered pretty good. Its the one hardware failure I see time and time again with my customers. If nothing is DOA, PSU will be first to die.

I know it's not exact, but my general rule of thumb is to push the PSU to it's rated efficiency, as a % of it's max load.

If a 1000W PSU is only 82% efficient, I wouldn't run anything more than 820W. If it's 92% efficient, then you could go to 920W.
Another way to look at it is to make sure the At-the-wall draw (from a kill-a-watt) is lower than the rated draw from-the-PC.

Reason for this is heat. Heat is the biggest cause for damage to components, and a more efficient PSU is also a cooler one, losing less energy in the form of wasted heat.

Hmmm I'm wondering if my PSU is my problem.

I build a 7950 x 2 miner last night.  I'm using a  700W Corsair modular power supply.  With both cards running the system shuts off, as if its a power related problem, about 20-40 mins in.

I just built it so haven't had much time to test theories.  I'd imagine this PSU would be enough for the sustained power drain...but maybe i should get a new unit...

Power supplies do have the ratings for a reason. A quality PSU brand/model doesn't care if you use 100% of the rated power, or maybe 101%-102% 24/7.

Antec might have a few usable ones on the very top-end of their product line, and Corsair has some bad ones like the gaming series (GS). Comparison of quality is very easy, if you pick something else than the more expensive than an average unit in a given power range, the odds are you have a low quality product with not realistic power ratings.

I find it difficult to figure out why people try to cheap on the PSU to save less than 50$ or so. It brings so much trouble to deal with those timebombs. And those savings are lost the very moment your system goes down due to a PSU giving up.

I would say for sure.  Read above m8...had same issue with a quality silverstone 700w supply. one of the best brands available IMO and it's just not enough for x2 7950s mining. Switched to a 950w antec and have had zero problems. Not a big fan of antec products besides their cases but its what was on the shelf at frys so...

Good quality power supplies are designed for 24/7 work at 100% of their rated DC power draw, not their at the wall AC draw.

Check out this review of an 850W power supply, where the reviewer tests it at 840W DC, and measures 960W at the wall, and he's happy with that: http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story3&reid=336

7950 has a TDP of 200W. 400W can't overload a 700W PSU unless its crap or has very low-amp multiple rails on 12V. There was something else wrong than exceeding the 700W load.

75w thru the PCIe slot and 75w thru the 6pin x2 = 225w maximum. As I dont have a killawatt not sure whats happening at the wall. If was a bad 12v rail on that powersupply I dont know. Suffice to say that the 700w unit wasent cutting it for me and the 950w fixed the issue. Figure at max TDP they are sucking 400w+, so that was leaving 300w for the rest of the system..which should have been fine. The AMD proc has a TDP of 100w. That still 200w+ for systems fans and the harddrive.

Moral of the story I think which has been beaten into the bush. Bigger is better. Dont cheap out on your powersupply.  :)

Truth. /thread

Good points, cap againg is important to factor in. Calculating DC power using is important too, but how would one measure the amps from a rail on the PSU. In my experience i would check the 12v rail at idle and then at load. If i see the rails voltage drop below 12v then the component is drawing too much power than the PSU can deliver.

Alot of PSUs are over engineered, but that does not count for a weak link inside the unit. All it takes is one part to be underspecified/defective and that theory goes to shit. And heat will ware out everything in the PSU much quicker, this is why people need proper cooling.

And dont forget sometimes when PSUs go out they take other things out with them :-/

My 700W Corsair is coming along nicely with my 2 x 7950 rig now that I've had time to work on the system.

The reason why it was crashing out before was because I *very* dumbly knocked one of the cards one of the last time I was fiddling with my fans. Some of the pegs/teeth were hardly half engaged -- surprised it even ran at for 20 mins and even more surprised I didn't burn out any parts with that dumb move of mine.

Reading this thread and some other articles recently on PSU's think I have new respect/understanding for Gold rated PSUs. Does seem like its a better choice in Wattage savings and reliability to go for the more expensive PSUs when they are going to be running 24/7 @ top Wattages like most miners are.

I dont know, but Im running 2x6950s on a 500w supply, I figured Im close to capacity but it should hold

At home I have 2 MSI 7950s running on an Antec HCG-400 (400 Watt PSU) inside my main rig inside a case.  I had to undervolt the cards but am able to pull 1050MH/s on 375W at the wall.

Remember as PSUs age their output capacity will decrease.  Efficiency will stay more or less the same but the midrange and crappy 600W PSUs will only be able to put out 500W on the 12V after a couple of years.  I think GOLD/Plat PSUs would be better at handling this degradation.

wtf.

Curious, anyone ever use top power for mining with 3+ GPUs? they have a 1000W gold certified on new egg for $99.99.... never heard of the brand, so I'm not exactly jumping on it. I also saw a decent coolmax 1200W 80+ gold for $160, but haven't heard of them either. Seeing as how I'm working on my first and only mining rig, I don't want to take a chance on an offbrand PSU that will end up crapping out on me within weeks.

I'm thinking of going with this one for my first rig, starting with two 7950's:

XFX P1-850B-BEFX 850W ATX12V 2.2 & ESP12V 2.91 SLI Ready CrossFire Ready 80 PLUS GOLD Certified Full Modular Active PFC Power Supply  -  http://www.newegg.com/Product/Product.aspx?Item=N82E16817207028

I'm hoping I'll be able to get a third GPU on it in the next month without having to upgrade or get an additional PSU. Any thoughts or experience with this particular PSU w/3 or more GPUs?

That makes perfect sense. Why are you so confused?

My 7970 undervolted to 950mV, 900MHz core, and 375MHz mem gets me 520MH/s, while only pulling 108W (Just the card, not total system). Temps are also crazy low, like 30-40C @ 40% fan (silent). 2 of these, and it's quote easy to obtain.

Well I could get even lower wattage if:
1) My main rig didn't also power 2 HDs in addition to the SSD boot drive
2) I ran an econo CPU instead of an I5-2500K
3) I actually spaced the cards with risers - as it stand they're separated by 0.5 inches so they both run warm/hot 70-80C

The cooler the cards are the less power they'll suck.  It's kind of a vicious cycle.  But it's my main computer and I never mine at home except now with the crazy BTC prices.  Once my Avalons and unicorn blood coated BFL Singles arrive I'll toss all but 2 cards haha.

My power costs me $0.40 since I got kicked up to Tier 5 just by mining on those 2 7950s even with the undervolt.  Don't move to SoCal if you want to mine with GPUs.

Ya I got 1HDD, 1 SSD, and an AMD 8-core 8120. I feel ya. ;)

not confused, only amazed how efficient the latest generation gpus are.

sigh.

back to the mining game again.

Ive got a 750w bronze rated PSU that runs 4 seriously overclocked 5850s (150w each without overclock). Only recently have I had an issue where I had to physically unplug the PSU and wait a few seconds before it would let me turn it back on (overdraw protection I believe). It's been doin pretty fine otherwise, and in the 1.5 years I've had it, only had this issue happen twice. I think I've definitely gotten my monies worth.


But otherwise, don't cheap out on power supply.