GPU underpowered for XFX 7950 + Sapphire 280x?

[Mk2vr6]

As above.

I have a 750w XFX psu (have a dell 1520w server psu, but waiting for pcie connectors) And with just the 280x it runs perfectly at 750kh/s.

If I tweak the 7950 and run it alone I can get 620kh/s no problem.

Run them together and after 10 mins the 280x drops to about 550kh, and the 7950 400kh/s.

Any ideas chaps?

Cheers

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[Mk2vr6]

BUMP

[Mk2vr6]

Any input peeps?

[prolom]

I have a similar problem with dual HIS 280x (i have a total of 4 actually). On two different boards with two different power supplies ( a Thermaltake 750 and a Corsaire 1000). A single card runs at 730 and cool, dual cards drop to 600/500 or 730/630 with some extensive cgminer tweaking and very hot. I don't know if it's a PSU issue, doesn't look like it in my case.

[Mk2vr6]

I have a similar problem with dual HIS 280x (i have a total of 4 actually). On two different boards with two different power supplies ( a Thermaltake 750 and a Corsaire 1000). A single card runs at 730 and cool, dual cards drop to 600/500 or 730/630 with some extensive cgminer tweaking and very hot. I don't know if it's a PSU issue, doesn't look like it in my case.

I'd of thought that 750w would be sufficient. My cards are slotted straight into the board, so only have an inch space - could be heat throttling? The 280x on top sits around 82' as it is sucking hot air straight in from the 7950 below.

Need powered risers here asap! Bought them last week and they still haven't turned up!!

[Mk2vr6]

I have a similar problem with dual HIS 280x (i have a total of 4 actually). On two different boards with two different power supplies ( a Thermaltake 750 and a Corsaire 1000). A single card runs at 730 and cool, dual cards drop to 600/500 or 730/630 with some extensive cgminer tweaking and very hot. I don't know if it's a PSU issue, doesn't look like it in my case.

Are yours open air or in a case?

[Mk2vr6]

I suppose I'll wait for powered risers to turn up - get them out in open air, and try again. Maybe the MOBO can't provide enough power, so the molex might help.

They where getting mega hot though:-

-280x mining at 81 with fans at 85%
-7950 sitting idle at 51'

I removed the 7950 below, and now it sits at 71' with fans at only 48%!!

[prolom]

Mine are in cases but the cases sides are open and they have tons of fans - those are aluminum lian-li cases. In the smaller case they are 83/82, fans at 90/92%, larger case 74/80 fans 77/80%.

A single card runs around 60 to 70 something with fans at 50-70...

I don't understand why hash rates drop so much though... They are 620/730 and 630/720... The cards are very similar and i tried switching them around with no results... Let me know if powered risers make a difference.

[Mk2vr6]

Mine are in cases but the cases sides are open and they have tons of fans - those are aluminum lian-li cases. In the smaller case they are 83/82, fans at 90/92%, larger case 74/80 fans 77/80%.

A single card runs around 60 to 70 something with fans at 50-70...

I don't understand why hash rates drop so much though... They are 620/730 and 630/720... The cards are very similar and i tried switching them around with no results... Let me know if powered risers make a difference.

Yeah, I've a funny feeling that the mobo cant provide enough power. Powered risers can push the extra 50w+ through the molex.

I was hoping they would turn up today but the postie has been and gone now 

[prolom]

Interesting to hear how it works out for you.

I have watched this video where they put together a 6x 280x rig with some insane hash rates. They  use non-powered risers but each card adds significantly to the draw from the motherboard, i think around 50W actually (that board was designed for mining though). They end up using 3 power supplies.

http://www.youtube.com/watch?v=WfqfEpanpig&feature=youtu.be

So i might give powered risers a try. Anybody can recommend good suppliers in the US? I looked on newegg but what they sell gets bad ratings...

I have some decent old 650w power supplies around, without pci-e 8-pin connectors. I wonder if something like this would work, to add to the 1000 that i already have:
http://www.newegg.com/Product/Product.aspx?Item=9SIA29716C8626

[Mk2vr6]

Interesting to hear how it works out for you.

I have watched this video where they put together a 6x 280x rig with some insane hash rates. They  use non-powered risers but each card adds significantly to the draw from the motherboard, i think around 50W actually (that board was designed for mining though). They end up using 3 power supplies.

http://www.youtube.com/watch?v=WfqfEpanpig&feature=youtu.be

So i might give powered risers a try. Anybody can recommend good suppliers in the US? I looked on newegg but what they sell gets bad ratings...

I have some decent old 650w power supplies around, without pci-e 8-pin connectors. I wonder if something like this would work, to add to the 1000 that i already have:
http://www.newegg.com/Product/Product.aspx?Item=9SIA29716C8626

Yes I think those molex converters should work.

Have a look here for risers - https://bitcointalk.org/index.php?topic=392536.0;topicseen

[prolom]

OK, I'm waiting for both the risers and the molex connectors. I was glad  I could pay in BTC.

Meanwhile to pass the time I plugged one 8 pin cable from another psu to one of the underperforming cards  (the psu only had one) and the hash rate jumped by 20. So it is a power issue - but it's not exactly an underpowered psu - more like what you said - the mb not delivering the power.

I've read this post (#19) that made sense (not enough power for vc ram), plus  the main psu is probably not delivering enough either through those 8 pin connectors.

https://bitcointalk.org/index.php?topic=268879.msg2974007#msg2974007

[Mk2vr6]

Have you tried --gpu-powetune 20?

I have added that to my batch file, and like magic I regained my 752kh on the 280x!!

Batch file looks like this now -

Code:

setx GPU_MAX_ALLOC_PERCENT 100
setx GPU_USE_SYNC_OBJECTS 1
cgminer.exe --scrypt -o xxxxxxxxxxxxxxxxxx -u xxxxxx -p xxxxxxxx -d 

0 -g 2 -I 13 -w 384 --lookup-gap 2 --gpu-engine 1085 --gpu-memclock 1500 
--thread-concurrency 8193 --temp-target 68 --auto-fan --gpu-fan 20-85 
--temp-overheat 87 --temp-cutoff 95 --no-submit-stale --gpu-powertune 20
pause

Still working on the 7950 sitting below it. Got them both using risers now and bolted to the side of the case with the side off for increased airflow.

I can't seem to get the 7950 stable though, it hashes at about 550kh for about 2 mins, then drops down to 300mhz gpu, and restarts itself like its throttling when temp stays around 70'c

[prolom]

Hmmm... Bottom line - in my case powered risers and an extra power supply made no significant difference other than lowering the temperature of the card that's outside the case  (16 degrees cooler, tested on one motherboard so far) .

Powertune affects my hashrate a tiny little bit, but i'd rather undervolt (mine is -20, I'll test power consumption when I get a chance). I'll play with it some more, now that I have all this stuff, but so far no positive outcome.

[spiderdk]

its temperature your issue, same here. I had to change and blow wind from a different position in order to work fine full time.

Test it, place it on a air conditioning room blowing wind direct in the middle of the cards or something like that.

[Mk2vr6]

its temperature your issue, same here. I had to change and blow wind from a different position in order to work fine full time.

Test it, place it on a air conditioning room blowing wind direct in the middle of the cards or something like that.

The 280x above works fine, can keep that at 70'c no problems.

The Cheap shit XFX 7950 DD below is the one crapping out. I've still not got it to sit stable at 500kh.

Maybe Temp is the problem, it seems to slow down as soon as it hits 75'c

Need my cable and connectors to come from China ASAP so I can use my server PSU and get it all open air!!

[prolom]

There's something else we are overlooking.

I deleted cgminer bin files (to start over) and the hashrates on both cards went down (to 500-ish). I had to play with my bat files settings to bring the rates back up - couldn't bring them to the same levels even by restoring the bin files and restoring the previous hardware configuration. It used to be 730/620 now it's 665/625 and my bat file is completely different now after a lot of work.

With the risers the temps are in the 70s.

Go figure...

[Mk2vr6]

Are yours in a case or open air?q

Might be worth looking at undervolting them to reduce heat?

Take a look at this link - https://bitcointalk.org/index.php?topic=395004.0