Litecoin build for noobs: 3x 7950s (1.8 MH/s) in a $10 crate case

[StarenseN]

Nice Thanks !

[kujina]

I run 3x MSI 7950s on an ASRock Mobo w/ Sempron 45w CPU. Using a 860w platinum Seasonic PSU (93% efficient), I pull about 690w at the wall (measured with a kill-a-watt). I run the GPUs overclocked and undervolted (1087 mV @ 1050/1400 clock speeds, although I'm not done tweaking).

850w is definitely fine for 3 cards. 4 GPUs would be a stretch.

Hi rbbrdckybk

I'm currently running 3 of the 7950's and I also have a 45w Sempron but my power monitor at the wall reads around 850w! Best case scenario is that I can use all four cards so I hope AMD FTW responds soon as I was planning to send back the psu's tomorrow. Tacotime the original poster states that his 3x 7950 crate setup only draws 625 watts.

Guys please help me out as the weekend is coming and I need to make a decision on sending the 3x AX850's back. Will undervolting make a significant reduction in power usage?

This is my setup:

MSI 7950 Twin Frozr III
AMD Sempron 145 2.8GHz 45W +heatsink/fan
Gigabyte GA-990FXA-UD5
2x 4gb ddr3
Laptop hard drive

[Marrs]

I run 3x MSI 7950s on an ASRock Mobo w/ Sempron 45w CPU. Using a 860w platinum Seasonic PSU (93% efficient), I pull about 690w at the wall (measured with a kill-a-watt). I run the GPUs overclocked and undervolted (1087 mV @ 1050/1400 clock speeds, although I'm not done tweaking).

850w is definitely fine for 3 cards. 4 GPUs would be a stretch.

PSU are rated at by power they are able to deliver to the system, not at their at the wall draw.

690W at the wall at 93% efficiency means your system is delivering 690W * 0.93 = 641.7W, which means you have about 220 W of capacity left on your 860W PSU.

You could definitely put another 7950 on there.

[Marrs]

Will undervolting make a significant reduction in power usage?

Yes.

[ma_rine_sa]

just putting it here for reference dual 5970 (4 cores total) on my computer pull 240*3.5=840watts ltc mining

if i am btc mining i underclock the memory to it's lowest and pull 240*3=720watts

[rbbrdckybk]

Undervolting makes a huge difference. I pull almost 900w at the wall at stock voltage. Undervolted I draw less than 700w, and I think I may be able to drop it a bit more.

Guys please help me out as the weekend is coming and I need to make a decision on sending the 3x AX850's back. Will undervolting make a significant reduction in power usage?

[AMD FTW]

Don't you think 850w is too small for 3 7950s? i have a 750w for my 2 7950 setup

A good 850w psu can power 4 7950's on an energy efficient cpu setup. I've been running my corsair AX-850 golds like this for a while and have a seasonic gold doing the same.

AMD FTW you cant be running the cards at full steam (I'm not talking about overclocked). I've tried four 7950's (msi Twin Frozr) on a Gigabyte GA-990FXA-UD5 motherboard with a sempron 145
and 2x 4gb ram with a new corsair AX850 and while mining with reaper power consumption is around 1100w!!!!

Obviously the system shutdown (after about 1 min). I got the corsair AX850 because they decent, reasonably priced and based on your testimony. But there's no way from my testing (yesterday) that a corsair AX850 or any 850w psu can power 4x 7950 cards used to their potential.

AMD FTW are you lowering the 7950 voltage/core speed or something, can I get your comments?

I've been running my corsair ax 850 for almost 1 year straight running on numerous setups. One of my setups has 4 7950's with an I3 2100. I have another Corsair AX850 running 5 6870's. Then I have a Seasonic X-850 running 4 7950s, and the fourth rig has a Corsair AX 1200 temporarily running just 3 msi 6950 twin frozrs. I just purchased an XFX Pro 850 which will be powering those 6950's in a week. All cards are run at what ever speeds they ship with. I believe 1 setup the cards are at 810 mhz, and the other setup is at 850 mhz. I prefer not to overclock the cards as for me its not worth the extra heat generated which equates to excess power being drawn.

I actually have another setup I'm working on now which uses dual XFX 850 pro's to power 6 7950's on an MSI Z77-g41 board with an I5 2500k

Don't forget if your overclocking your gpu's, 7950's take significantly more power. Typical 7950 stock wattage is right around 175 watts not overclocked. The Specs for a 6 pin connector is 75 watts, and the pci e buss is rated for 75 watts as well. Which means the maximum safe wattage according to those specs is 225 watts a cards since the 7950's have two 6 pin connectors and 1 pci express connector. AMD specs the max TDP of these cards as 200 w. If the card has an 8 pin pci express connector, then the rated load for that connector is 150 w and that is why the 7970 is rated for a max TDP of 250 w. So as long as you don't overclock, theirs no reason an 850 w can't supply enough power for 4 7950's. Don't forget at the wall you'll see a higher wattage than whats actually being pumped out because of the psu inefficiency. Even most gold psu's cant hit 90 percent efficiency when the psu is being run at 90 percent or more of its rated capacity. A fully loaded 850w GOLD psu will probably read right around 950-1000w

[rbbrdckybk]

PSU are rated at by power they are able to deliver to the system, not at their at the wall draw.

690W at the wall at 93% efficiency means your system is delivering 690W * 0.93 = 641.7W, which means you have about 220 W of capacity left on your 860W PSU.

You could definitely put another 7950 on there.

Yup, I'm aware that PSUs are rated based on delivery after efficiency loss, but I still think 4 will be a stretch.

I pull about 900w during boot up (eg: until MSI Afterburner loads and drops the voltage to the GPUs). Adding a 4th card means that I'd be significantly over 100% of the rated delivery on my PSU during boot up. I'm not sure whether the system would even make it to the desktop without shutting down. Even if it did, I'd basically be running the PSU at ~100% capacity 24/7 with 4 cards, which isn't going to be great for it's lifespan.

[kujina]

Will undervolting make a significant reduction in power usage?

Yes.

Thanks guys for the clarifications, I'm feeling less stressed now! I have four new AX850's in total! I definitely will attempt some voltage underclocking today asap.

AMD FTW my cards are at stock too, did you undervolt?


a. Does undervolting hurt performance while in turn lower power consumption ?

b. What would be a good starting point for voltage for a MSI 7950 Twin Frozr III (default 880mhz core 1250mhz mem)

c. is it just the core that's undervolted?

...Thanks...


...Thanks...

[rbbrdckybk]

My cards run completely stable at these settings:

1087 mV (undervolted from 1250 mV stock)
1050 mhz core clock
1400 mhz memory clock

I get about 625 kH/sec on each GPU in cgminer.

Only the core & memory speeds affect performance. Undervolting will just make the card draw less power. At some point, undervolting too much will make the card unstable, so there is a limit to how far you can go.

Thanks guys for the clarifications, I'm feeling less stressed now! I have four new AX850's in total! I definitely will attempt some voltage underclocking today asap.

AMD FTW my cards are at stock too, did you undervolt?

a. Does undervolting hurt performance while in turn lower power consumption ?

b. What would be a good starting point for voltage for a MSI 7950 Twin Frozr III (default 880mhz core 1250mhz mem)

c. is it just the core that's undervolted?

...Thanks...

...Thanks...

[AMD FTW]

The AX-850 has a seven year warranty for me in the states so I really dont mind if the psu ever did go down as I have a spare one. If your bumping up the clocks to get equivalent hash rates of a 7970, then your cards will be pulling 7970 watts. On a side note, I've drawn 5 7950's on a AX 850 for a few days and had no issues. This would NOT recommend, and I did it for the curiosity to see if I could undervolt 5 cards and run them off a AX850 and it worked fine for days. I had 5 cards running at 800 mhz each and were undervolted to 875 mv if I recall correctly. I did this roughly 6 months ago. What had me worried more than overloading the psu was their wasn't enough cables to run to the PSU so I had to run 2 6 pin pcie power connectors off of 1 molex cable and also had to do the same with sata to 6 pin pcie power connector.

[kujina]

What had me worried more than overloading the psu was their wasn't enough cables to run to the PSU so I had to run 2 6 pin pcie power connectors off of 1 molex cable and also had to do the same with sata to 6 pin pcie power connector.

As you obviously know the AX850 comes with 4x pci-e connectors so I'm also using 2 molex pci-e adapters on both of the two (4x) molex cables, is this not ok?
Have you ever tried running 4x non-undervolted 7950's using the AX850?

[digitalindustry]

here's one of my rig 4x5850 
Used case ~ 2.5$
4 riser 1x->16x ~ 20$
Giga P31+2GB ddr2+Dual E3300 ~ 50$ (all used)
Corsair TX750 new ~ 120$
4x 5850 ~  440$,all of them are under warranty

all cost ~ 630$
with this rig,i can get about 1.5-1.6Mhash when mining ltc 

sir that is a piece of ....art!
Fantastic !

[efx]

Almost all of AMD's hardware is slightly over-volted stock, CPUs included. I assume the slight over-volt is just to increase yields. If you aren't going to OC, bump that voltage down asap.

[Valle]

I built recently 4x7950. Mining on full speed(gpu 1100 mem 1400) takes more than 1400W. 160W while idle.

[Vigil]

I built recently 4x7950. Mining on full speed(gpu 1100 mem 1400) takes more than 1400W. 160W while idle.

Jeebus! Are you serious? From the wall?

[txmasut]

I built recently 4x7950. Mining on full speed(gpu 1100 mem 1400) takes more than 1400W. 160W while idle.

Need to get that thing checked, lol.  I have a 5x7950 setup mining 650 hash each and I'm only at around 1080 watts for the system and all five videocards.

[AMD FTW]

What had me worried more than overloading the psu was their wasn't enough cables to run to the PSU so I had to run 2 6 pin pcie power connectors off of 1 molex cable and also had to do the same with sata to 6 pin pcie power connector.

As you obviously know the AX850 comes with 4x pci-e connectors so I'm also using 2 molex pci-e adapters on both of the two (4x) molex cables, is this not ok?
Have you ever tried running 4x non-undervolted 7950's using the AX850?

For the AX-850 and other psu's that only have 4 pcie power connectors 6 pin or 8 pin, use these to besides the molex to help power the gpus

http://www.monoprice.com/products/product.asp?c_id=102&cp_id=10226&cs_id=1022607&p_id=8494&seq=1&format=2


Also if your having trouble and for some reason you can't get them to run with all 4 cards, you can always daisy chain the psus together. I paid right around $100 for my seasonic x series 850w with rebate and around $110 for my xfx 850 pro gold psus. I'm daisy chaining 2 xfx 850 pro psu's now to power 6 cards on a board. I decided to go this route since 2 psu 850's were easily cheaper than a 1200w + psu if I decide to switch out the 7950's to 7970's down the road.

http://www.legitreviews.com/article/1698/


edited for:
On a side note, if you use dual psu's, its a good idea to power each card off the same psu and not to split 2 power supply's powering 1 card.

[kujina]

Thanks AMD FTW

Msi Afterburner didn't have an effect on the voltage of my msi cards but Sapphire TRIXX did instead (my drivers are 13.1 for anyone interested). So I have managed to use a AX850 per 4x 7950's : )
You sure are able to get those power supplies nice and cheap, I paid pretty much double! (I'm not in the US though) I'm on ebay ordering some of those of those SATA 15pin to 6pin PCI converters now.

[Vigil]

Sweet!! Got my 7950s running at 650 Kh/s. That is maxed-out though. It starts warming up a little over 80 C. Gonna have to bring it down some, if I can settle in at just over 620 would be nice.