Ermmm...probably a stupid question but...

[Mr.Meerkat]

So can I run 3 7950s (original 150-180W cards) or even 4 7950s off a single 850w PSU (XFX 850w XXX edition)? Since the original 7950s were so power efficient (in the sense that they only drew 150-180 watts), I'm sure it's fine running 3 cards with it right? as 180x3=540watts leaving 350watts (more like 300w once you factored in efficiency and how the 12volt rail only delivers like 800watts)  for the rest of the system...

[DrDray]

8 minutes ago, Mr.Meerkat said:

So can I run 3 7950s (original 150-180W cards) or even 4 7950s off a single 850w PSU (XFX 850w XXX edition)? Since the original 7950s were so power efficient (in the sense that they only drew 150-180 watts), I'm sure it's fine running 3 cards with it right? as 180x3=540watts leaving 350watts (more like 300w once you factored in efficiency and how the 12volt rail only delivers like 800watts)  for the rest of the system...

Use this here to work it out

http://powersupplycalculator.net/

[Mr.Meerkat]

2 minutes ago, Josh.Drayton said:

Use this here to work it out

http://powersupplycalculator.net/

Ah, 750Watts, must be fine (4 7950s including a potato C2D and a stick of ddr2 ram )...don't trust them...but if it says 750 then I must be fine  

[Sauron]

PSU calculators are not too accurate, they are all right to get a general idea but not for exact calculations.

 

I don't think you can handle 4 cards off of that psu. A single 7950 can draw almost 200 watts at peak load (at stock speeds, when overclocked it can get over 400W). 3 of those would already be sucking potentially 600 watts all by themselves. If you consider you have the rest of the computer to run as well, it would be hard for a fourth card to fit.

 

Efficiency affects how much power is drawn from the wall, not how much power the psu delivers to the computer. An 850W psu will deliver 850W to your pc. It may draw 950+W from the wall, but that is not what we're concerned about here.

 

As for 3 cards, if you want to play games with 3 way crossfire I must suggest you give up the idea. Not that you can't do it, but the performance gains are really not worth the pain in the butt of a 3 way setup. 4 way is even worse of course.

 

-edit-

 

oh and if you'll use it with a c2d you won't be able to use even a single card to its full extent, let alone 2 or 3.

[STRMfrmXMN]

3 hours ago, Mr.Meerkat said:

So can I run 3 7950s (original 150-180W cards) or even 4 7950s off a single 850w PSU (XFX 850w XXX edition)? Since the original 7950s were so power efficient (in the sense that they only drew 150-180 watts), I'm sure it's fine running 3 cards with it right? as 180x3=540watts leaving 350watts (more like 300w once you factored in efficiency and how the 12volt rail only delivers like 800watts)  for the rest of the system...

Ehhhhh I wouldn't do 4-way Crossfire. Yes you can have them all not overclocked in one 850W unit system but why would you TBH?

[Mr.Meerkat]

11 hours ago, Sauron said:

-snippy-

 

8 hours ago, STRMfrmXMN said:

Ehhhhh I wouldn't do 4-way Crossfire. Yes you can have them all not overclocked in one 850W unit system but why would you TBH?

Mining...nuff said?  (but in seriousness, I'm only wanting to not use my 430w evga 80+ white PSU...but I don't see why it can't power a 7950 without blowing up as it managed to power a 560 for more than a year with no issues ).

[it_dont_work]

Maybe, you'd need to check the exact specs of your psu, just because it's an 850watt supply doesn't necessarily mean it will supply 850watt on the 12v rail.

[Mr.Meerkat]

1 minute ago, it_dont_work said:

Maybe, you'd need to check the exact specs of your psu, just because it's an 850watt supply doesn't necessarily mean it will supply 850watt on the 12v rail.

 

12 hours ago, Mr.Meerkat said:

how the 12volt rail only delivers like 800watts

Teee hee hee (and it's actually 840w stated by XFX on the 12v rail, just checked)

[it_dont_work]

it fine, just keep a fire extinguisher close...and of course read everything first not like some people.

[Mr.Meerkat]

2 minutes ago, it_dont_work said:

it fine, just keep a fire extinguisher close...and of course read everything first not like some people.

Hehe...3 cards it tis then...430w 80+ white, pls no blow up...it will literally be powering a single card and a c2d that's going to be idling...hmmm...

[Sauron]

5 hours ago, Mr.Meerkat said:

 

Mining...nuff said?  (but in seriousness, I'm only wanting to not use my 430w evga 80+ white PSU...but I don't see why it can't power a 7950 without blowing up as it managed to power a 560 for more than a year with no issues ).

Well, ONE 7950 is certainly not a problem for an 850W psu, in fact you may be just fine with 500 or 450. If the evga works fine you may want to try sticking to that before you go out and buy something else.

[Mr.Meerkat]

1 minute ago, Sauron said:

Well, ONE 7950 is certainly not a problem for an 850W psu, in fact you may be just fine with 500 or 450. If the evga works fine you may want to try sticking to that before you go out and buy something else.

My original plan was 3 on the 850w and one on the 430w...but I'm still skeptical with the quality of that 430w PSU so I had the idea of 4 on the 850 but meh, 3 on 850 and one on 430 it tis then  (does 8 pin to 2x6pin adapters exist? so I can stop using the molex to 6 pin cable with the evga PSU as it only has 1 6+2 PCIe power connector)

[Sauron]

1 minute ago, Mr.Meerkat said:

My original plan was 3 on the 850w and one on the 430w...but I'm still skeptical with the quality of that 430w PSU so I had the idea of 4 on the 850 but meh, 3 on 850 and one on 430 it tis then  (does 8 pin to 2x6pin adapters exist? so I can stop using the molex to 6 pin cable with the evga PSU as it only has 1 6+2 PCIe power connector)

I don't think mining on 7950s is a very good idea, at this point they are old cards and they are not all that light on power consumption. You'd find it hard to make a profit.

 

If you still want to do it, even a meh power supply has few chances of actually damaging your card, so I wouldn't worry about it. Molex adapters are just fine, you won't lose any performance by using those.

[Mr.Meerkat]

14 minutes ago, Sauron said:

I don't think mining on 7950s is a very good idea, at this point they are old cards and they are not all that light on power consumption. You'd find it hard to make a profit.

 

If you still want to do it, even a meh power supply has few chances of actually damaging your card, so I wouldn't worry about it. Molex adapters are just fine, you won't lose any performance by using those.

Ehhh...22MH/s at around 175Watts~ (7950) vs 28MH's at around 300watts (290x) I wonder which one is better in terms of hash rate to power consumption  plus you can get 7950 for like 60-70 quid easily while 290Xs costs more than 150 each so...

 

Well the EVGA is the only Meh PSU I have so...you know...

 

edit, forgot to mention the hash rates are my own experience

[Sauron]

Just now, Mr.Meerkat said:

Ehhh...22MH/s at around 175Watts~ (7950) vs 28MH's at around 300watts (290x) I wonder which one is better in terms of hash rate to power consumption  plus you can get 7950 for like 60-70 quid easily while 290Xs costs more than 150 each so...

 

Well the EVGA is the only Meh PSU I have so...you know...

 

edit, forgot to mention the hash rates are my own experience

Depends on what you're mining. Bitcoin for example wouldn't get you even a tenth of your power bill back - you can't mine those effectively with gpus anymore.

[Mr.Meerkat]

4 minutes ago, Sauron said:

Depends on what you're mining. Bitcoin for example wouldn't get you even a tenth of your power bill back - you can't mine those effectively with gpus anymore.

Hehe, mining ETH, I will make how much I've spent on the whole system (£146) in around 1 to 1 1/2 months so...yeah  (with 40MH/s of hashing power not including my 290x and 2 of the 7950s)