Topic: How many liquid-cooled 6990s can a 1500W PSU push? (Read 5096 times)

Thanks for all the great advice.  Maybe I was getting too ballsy with thinking I could pull off water-cooling [easily].  Although - I agree that water cooling will push back the 'break even' point/day, since gear is a fixed cost - after the break even point it doesn't matter: variable income/profit is the same (and I've got a quieter/cooler rig and more assets to sell off if necessary).

Anyway, I signed up for nowinstock (thanks for the pointer!) and will stick to air-cooling for now - and probably the 5950/5970 instead of the 6990s. 

Thanks again, and thanks for keeping me in check!

There is a very easy and cheap solution. Get a second motherboard!

I wouldn't say the reservoir is to stabilize the water temp. The reservoir is for a few things mainly. 1 is so that the pump has a constant and hopefully bubble free supply of water, that's why the pump is usually bellow the radiator, so gravity helps to keep the pump always wet. The reservoir can also be used to keep the temperature of the loop down temporarily. If you have a decent sized reservoir it will take longer for all of the water to heat up. Of course mining is a 24/7 constant output of a large amount of heat, so it wouldn't keep the temperature down long unless you had a ice chest as a reservoir lol. Another thing is a reservoir makes it easier to drain your loop and perform maintenance such as adding antimicrobials to it.
But I agree that he would probably need 2 rads. You're right that the 2 GPUs wouldn't heat up the water THAT much, but I would bet the 3rd GPU would be a lot higher with only one reservoir.

buy 4 and ship one to me. i'll pay with 3 months of 1.1Ghash/s.

You should follow the advice of what water coolers are telling you.  Don't do it unless you're fine with throwing away money and know what you're doing (or are willing to spend a bit of time learning).  It's not going to be easy/cheap to cool several of these cards.

Whether you should go for 3 or 4 cards depends on whether or not you want to overclock them.  With 3 overclocked cards, you can easily approach the same power usage as 4 cards at stock speeds.  With 4 slightly overclocked cards and some memory underclocking, you could be hanging around 1800w, depending on how good the PSUs are.  You'd want two PSUs to do 4 cards.  With 3, you're pushing it with a single PSU and should go for 2 PSUs.  You might be looking at 900-1300W just for the cards themselves.  You'll want to stay under 1440W total draw on a 120V/15A breaker, or 1920W on a 120V/20A breaker to be on the safe side.  3 cards would be safer and cost less.  4 cards is a fire hazard.

Disadvantage to mining on water -- Expensive, harder to make back money.

No. The processor consumes power, as well as the motherboard, HDD (and very slightly the RAM).

Even a Sempron 140 consumes 45 watts so it's going to be more than 1500W

I would say 3x at most.

There isn't any disadvantages with mining on water.  In fact you can overclock and get way more Mhash with low noise and little heat.  My 6990 has been mining forever @ 990 MHZ and is currently at 50C.  It gets 850 m/hash.   Can up voltage and easily hit 1025.

Unfortunately water cooling is not easy, although I think it may be easier with mining.  As you have no case you won't have to worry about shit not fitting and buying the wrong stuff.

I'd hop over to OCN and review the water cooling threads.

The way I understand it the concept of the reservoir is to stabilize the temperature of the water in the loop. It's not quite the same as air where you blow hot air on to a hot card and out the other side comes even hotter air. The specific heat of water is vastly higher than that of air (about 4x higher in fact, 4 kj / kg DegC), as well as being much denser (roughly 1000x the density, 1000kg / m^3), meaning it is able to absorb much much much more heat without necessarily increasing in temperature as much.

You will still need more than one radiator as I recommended earlier because a single radiator won't be able to dump enough energy from the loop to the environment however.

my standard rig configuration ist a 1250 W psu, msi mobo, 2gb ram, no hdd/ssd, with 3 aircooled 6990 in overdrive mode - however i'm pretty much on the edge with the psu's  the cards are almost stable until 915-925 mhz core overclocking, however the psu will giveup after a few minutes (=crash/kernelpanic) - so finally i'm stable at around 900 mhz - 80-90% fanspeed - 75-90 degree coretemp

The 6990 is rated for 375W by AMD. With 4 of them at 375W you'd be right at 1500W. Realistically they probably won't draw that much, I would guess 300W+. Maybe someone with a killawat can step in, I think the 2x 1KW PSU is the best solution to run 4 safely.

Also, one thing you may not have thought of regarding water cooling is the loop order. You're going to have 3-4 6990's and only one radiator from what I understand. No matter what way you set it up one GPU is going to be getting very warm water.

Reservoir -> Pump -> GPU1 -> GPU2 -> GPU3 -> Radiator ->

That might be too much heat for GPU3 to handle. You might need to split it up and put in 2 radiators, especially if you get 4 cards.

Check out a water cooling forum though for better information. xtremesystems and overclock are good sources of information and help. It's a lot of work, and a pain in the rear, but also rewarding.

Just run two 1kW PSUs. Setup isn't hard, but not that easy either. Done.

Just going to throw this out here, if you've never water cooled before...

WATER COOLING 4 DUAL GPU CARDS IS INCREDIBLY DIFFICULT. Aside from the fact that That 6990s were already terrible MHash/$ cards, the water cooled version is more expensive, and requires a beefy loop to do it (can cost a couple hundred on top). You will need to remove every watt you put into the system via water, and for a healthy system temperature you will need roughly 2 high quality (BlackIce GTX360 level) triple rads for the 4 cards with high performance high rpm fans.

If you don't enjoy the sound of metal slicing your ears you may consider 2 quad rads, or 3 triple rads. Don't cheap out on the rads either. If you go with a Rasa for example you add another radiator.

So anyway, warnings aside, if you want to build a crazy ass setup that will be a pain in the ever loving ass then I believe the only 1500W worth its grain of salt that I know of is the silverstone strider (the ultra x4 is ok but not great afaik). And sadly that is only rated for 1300W on the 12V rails. So I would say that 4 cards would be... a bit scary for 24/7. It might be able to handle it in all truthfulness, but I'd personally be a bit worried abot the whole thing, especially if you dump the watercooling loop on the same PSU.

So if you're going 6990s overclocked + wc loop on a SS ST1500 I'd personally recommend sticking with 3. If you are the type that enjoys throwing money around like you say, you could try 4 as a bit of nailbiter experiment. Please tend your rig though.

I'm running (3) air cooled 6990's on a Corsair AX1200 PSU, all cards are in the stock default position though.

It's been running with two cards for almost a month now - and 3 cards for the past week. Not sure about your argument though - there are plenty of 6990's around - you just need to look. There's a bunch on eBay as we speak, and you'd easily pay the $150-200 premium in water cooling equipment alone.

www.nowinstock.net is your friend. NewEgg auto-notify is awful and does NOT work. I just received two more Sapphire 6990's after NewEgg got in 100+ last week - but I had to order them as soon as receiving the email. I've got a total of 5 now - and I'm done buying.

Unless there is a reason you want to jam it into one rig, I wouldn't. If you have one main computer, you want to keep one main computer, you use it for other stuff but also want to mine it as hard as you can. Then that makes a little more sense.

Otherwise it's more cost effective to just get two systems. Or three.

As for the question, fairly sure 3 is as many as you want to put into one system. If you want 4, then get two systems and put two in each. To run 3 you'd have to with linux as I'm fairly sure there are issues with more then 4 gpus (3 6990s would give you 6 gpus) on windows. I'd go two 1200 watt psus and cooling should be quite a bit easier.

For a single beast of a rig, water cooled, 1500w, 3 6990s, running linux should work great as far as I know.

So what type of outlet do you intend on plugging the 1500w PSU into?

lol

Let me guess...you never used water cooling before and you want to go big the first time you use it? Not the best idea. It takes time to setup a water cooling loop. You're going to lose 24 hrs just testing it for leaks. Then you have to install it and test again. This is the proper way but you can always be half assed about it at your own risk. One 3x120mm rad will only be barely sufficient for two 6990. I wouldn't put more than two 6990 on a 1500w psu. It can be done but it's always better and safer to have headroom. To be safe electrically speaking, a max of two 6990 per circuit would be wise. The costs associated with something like that would outweigh any thought of profit especially at the current difficulty level. Good luck.

each 6990 pulls around 375watt, when the switch is in the overclock position it pulls 425watt each, add allt he other shit together mobo fans water pump ect.. I am guess you should be good with 3 of these on that power supply... 4th might be alittle too much with all your other overheads..

Well my rigs with two 6950s, plus system components (single core AMD sempron and 1 gb ddr 2 ram), use almost exactly 500w from the outlet (confirmed by kill-a-watt meter). I'm using 80 plus certified power supplies that are around 80% efficient, so that means that in actuality the cards are using 400 W of the power supply's rating (I believe they're rated on draw from parts, not draw from outlet but I could be wrong). Anyway, the chip is only using about 30 W of that and the rest of the system maybe 20 (just guessing), so that means each card is probably taking about 225 W from the power supply.

Now a 6990 is two chips, and has roughly the same draw as two of my 6950s. So that means it probably uses around 400 W each card. Given that you want a little breathing room, I would say you can't put more than 3 cards on one 1500 W power supply.

The better idea I think would be to buy two cheaper 1000W power supplies to run four cards (if you want to go the 4 card route).