What hash rate can I expect from 3 x 7850s?

[btcminer021]

Putting together a new rig. Using the below. Can anyone guess the expected wattage usage and hash rate?

GPU: 3 x SAPPHIRE 100355-1GOCL Radeon HD 7850 1GB 256-bit GDDR5 PCI Express 3.0 x16 HDCP Ready CrossFireX Support Video Card OC Version
PSU: 1 x Corsair Professional Series  HX 850 Watt ATX/EPS Modular 80 PLUS Gold (HX850)
MB: 1 x ASRock MB-970EX4 Socket AM3+/ AMD 970/ AMD Quad CrossFireX& nVidia SLI/ SATA3&USB3.0/ A&GbE/ ATX Motherboard
CPU: 1 x AMD FX-4100 Zambezi 3.6GHz (3.8GHz Turbo) Socket AM3+ 95W Quad-Core Desktop Processor FD4100WMGUSBX
RAM: 1 x Corsair Vengeance 8 GB ( 2 x 4 GB ) DDR3 1600 MHz (PC3 12800) 240-Pin DDR3 Memory Kit for Core i3, i5, i7 and Platforms SDRAM CMZ8GX3M2A1600C9
Case: 1 x LIAN LI PC-7HB Black Aluminum ATX Mid Tower Computer Case
CPU Cooler: 1 x COOLER MASTER Hyper 212 Plus RR-B10-212P-G1 "Heatpipe Direct Contact" Long Life Sleeve 120mm CPU Cooler Compatible with Intel 1366/1155/775 and AMD FM1/FM2/AM3+

I've already done the math and it looks like 1300MH/s? Max power usage would be about 750W. Anyone see any issues with these numbers?

[DrG]

Which coin are you going to mine (it affects the wattage use)?

[btcminer021]

BTC for about a month then probably LTC and converting them to BTC to cash out

[Gator-hex]

You won't get 1300MH/s unless you run 4 cards.

You can get 900MH/s easy, 1000MH/s if you push it more and don't mind it crashing now and again.

Only 1xPCI-E each, 100-120w per card, 750w is more than enough.

[mrSprinkles]

I'm getting around 350-360 KH/s on my 7850 mining LTC.

[DrG]

BTC for about a month then probably LTC and converting them to BTC to cash out

Right now BTC mining is on par with LTC as far as income.  If LTC difficulty keeps going up there would be no point converting, just stick mining BTC.

[btcminer021]

https://en.bitcoin.it/wiki/Mining_hardware_comparison

From what I can tell from the table and others' experience, 300-400MH/s per card would be doable, no? I guess time will tell!

[Gator-hex]

You wont see 400MH/s unless you run 7870s

I think sometimes people quote unstable MH/s on that page that only last a few minutes.

Anything over 330MH/s will crash a lot.

[DrG]

On that mining hardware page what you find is a lot of extremes.  Like the person only getting 525MH/s with a 7950.  Or somebody mining with a 7970 outside in a snowy area so that they are able to overvolt the card to crazy voltages and fan speeds.

Any time you run multiple cards the weakest card will bring the rest down even if you use independent settings.  The heat from each card increases the power usage by requiring more fan speed and voltage to remain stable.

Expect 310 from each card, and anything above that is good luck and some skill with tweaking.

[chaosgs]

Running 2 rigs (soon to be 4 rigs) with 4 7850s each.

Each GPU gets 320 M/hash at 1095 OC. For a 24/7 operation I cant get them to go higher. Also its open air non cased, in front of a window AC unit.....

7850's are the best bang for buck, unless you can get 7950's on sale.

[chaosgs]

Oh I forgot the best part. Im pulling 580 watts out of the wall with those 4 gpus. I bought a watt meter to keep tabs on my power. Doing math X3 would prob consume 450 watts.

[btcminer021]

Spot on! 3x GPUs is about 460 Watts!

I was getting about 750MH/s with 3x GPUs, but the middle one was running too hot. Now with 2xGPUs I get 525MH/s, so about 250MH/s each. This is stock. I will start OC tonight. I'm hoping for at least 300MH/s each OC. Next step is to get risers so I can get some more airflow between the cards. Suggestions to support the cards without PCI brackets?

[btcminer021]

FYI I've got only two running right now due to high temps with the middle card. Need to see how this is going to work in a closed case with three cards. May have to seriously change the plan.

With 2 x 7850, both OC to 1200MHz Core, 1300MHz Memory @ 1.18V, fan speed 85%, about 330Mh/s with cgminer intensity 9, and about 73-75C each under load for a day.

I'm petty happy with this, but certainly hoped for more! I could play more but am OK for now until I get a few BTC. Any suggestions? Would changing the intensity help at all?

[Extornia]

Your clocks are bad and you should feel bad. Experiment. My perfect ratio is 912core and 1250 mem, (this is a 5770 and a 6770) I get 210kh/s. If I put it to 913core i drop to 160kh/s and 1250+ mem drops aswell. Also this is about scrypt. There is no point doing bitcoin with only those type of GPU's. Do litecoin.

To cool your gpu's get 2 fans, pushing air inbetween the gpus.

[Operatr]

Well this is handy info, I am typing this post from my new mining rig  3x 7850's also.

These are Sapphire HD 7850 OC's,  they have an open air style dual-fan heatsink, we'll see how they handle the heat after some OCing. These things can be had for about $165 all over the place, seemed to be the best deal for the power they can deliver.

[Operatr]

Ok, it was pretty easy to ramp these Sapphire's up to around 320 Mhash/s from 250 stock, with a core clock of 1106 and a slight voltage bump with the TriXX utility, no problems so far. I can see the middle card getting fairly warm, Ill need to throw some more fans around them to go further probably. Grand total 960 Mhash/s

[chaosgs]

I cant get my cards to stay stable at 1100 core clock, so I keep them at 1050. Sucks because they dont go over 70C, tend to stay around 60C.

[killerbread]

Why do you need a case? You're going to trap a lot of hot air inside.

[btcminer021]

Can you guys post you OC settings like core and men clocks, voltage, fan speeds,etc? I've hit a limit and my middle card is over 100C!

[shockr]

Ive been mining litecoin so im not too sure how the numbers compare.

I have 3x 7850 @ 1100 Core/1200 Memory, average around 380KH/s each

./cgminer --lookup-gap 2 -I 20 --thread-concurrency 8192 -w 256

https://i.imgur.com/oD2ovzF.png