Questions regarding PSU requirements for SLI config + Motherboard

Telwen

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Hello everyone!

Ok, straight to business.

Im in a situation where its required of me to upgrade a PC's hardware for 3d gaming. But unfortunately dont have the big bucks needed to swap it all out with new things.

The PC is a 3d gaming rig, however it will struggle with new 3d games such as Fallout4, the witcher 3 etc. At least in theory!

So what im thinking of doing is adding a 2nd 580 GTX 1.5gb (GV-N580ud-15i rev.2.0) in a SLI config to boost gaming performance overall.
I already possess a 2nd 580 GTX of the same kind from another unused PC.

The motherboard im using (Asus M4A87TD/USB3) does not support SLI, so ill need a new one with same AM2+/AM3 socket support.

CPU is an AMD Phenom II 965 Black Edition 3.4ghz(can be swapped out with an AMD Phenom II X6 1090T Black Edition) But to my understanding thats a downgrade for gaming purposes.

Im using a 750watt Power supply. And im not too sure about power management with SLI. Ive never attempted a SLI setup before. But from looking at the card it uses up to 244 watt max each.

So, 244*2 = 488 watts for the SLI. Resulting in 750-488= 262 Watt left for the rest.
The CPU uses max 125 Watt so 262-125= 137 Watt left. In my ears and eyes it seems enough but what do you guys say?

Hope you guys can help me out.

Telwen
 

clutchc

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According to this, http://www.realhardtechx.com/index_archivos/Page362.htm dual GTX 580s will require a 900W PSU. That seems a bit high, but they may be assuming the worse case scenario for a PSU. I used to have a pair if GTX 570's running with my 850W XFX PSU with plenty of headroom left. But I think 750W will be cutting it close. Probably too close. Best if you could specify the exact make/model of your PSU to be sure.

But to be honest, I doubt either Phenom II would be able to keep up with 2 x 580s. Nevertheless since you already have both cards, there's no problem finding out by actually testing them.
 

Telwen

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I did some more digging, and did some more research. Max power consumption of a single 580 GTX during heavy 3d gaming/benchmark seems to be 405 watt. So my 750 Watt PSU will certainly not do.

How do i find out if my CPU is strong enough for 580 SLI? Is there a way to calculate that?

 

clutchc

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405W! That must be total system wattage. The GTX 580 would burn up before it got close to that kind of power draw.

As to your 2nd question, it is basically just experience. I have a Phenom II X4 965 BE @ 4.0 GHz. It is just able to keep up with my GTX 960 FTW+ at 1480 MHz and my R9-280 with a mild OC. I ran the Ph II with my R9-290X and it choked badly. (The 290X is comparable to the GTX 970)
 

Telwen

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I used GPUBoss as reference http://gpuboss.com/graphics-card/Nvidia-GeForce-GTX-580

Ive read that GPUBoss sucks, but cant really find any info about why that is.

So i also looked here http://www.anandtech.com/bench/product/1444

This site says 346 total system power consumption. But does not say what other hardware was used to do the tests. But one can only assume its at least is a 125watt CPU?

 

clutchc

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No, you can't assume that the CPU was a 125W processor.
The GPU Boss wattage confirms my suspicion; the idle and load power demands are for the entire system using one GTX 580. The TDP for the 580 is 244W. The Anandtech site shows a bit less than that with their setup running C3 and Furmark.
 

Telwen

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Its correct the TDP for the 580 is 244w. But thats not the max watt usage of the card, it can be much higher.

Regardless, I think its best to follow the recommendations of the manufacturers and get a 900w+ PSU.

That however mean I have to wait a bit longer before i upgrade.
 

Telwen

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[Update]

So i bought a "watt-o-meter" and plugged the PC to it. Surprisingly the old PC can run Fallout4 reasonably well at "roughly" Medium settings. Haven't tested FPS at higher settings yet, will have to do that to push the GPU and see if it consumes even more Watt. So far the Max Watt usage is 413.3 Watt for entire system while playing Fallout4. Idle Watt usage was roughly 100-110Watt.

Ill try to remember to update this post with exact game settings later.

The entire system is comprised of:
PSU: Corsair CX750 Watt
CPU: AMD Phenom II 965 BE 3.4 GHz 140 Watt.
Motherboard: Asus M4A87TD/USB3
GPU: Gigabyte GeForce 580 GTX 1.5gb (GV-N580ud-15i)
Memory: 8GB DDR3 Corsair at 1000Mhz (don't remember model)
Network card: Wireless card (don't remember name/model)
HDD1: 500gb 6Gb/Sec (Don't remember model)
HDD2: 2TB 6gb/sec Western Digital (Don't remember exact model)
DVD: LG DVD Burner.

Why on earth they recommend a 600watt PSU as MINIMUM I simply cant grasp. Its impossible to use that much Watt for a single GPU or single - GPU system even.

Ill try to keep everyone updated with further date/information.
 

maxalge

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they bloat wattage recommendations to cover bad power supplies like yours

you need to override tessellation to something like 8x, and turn off things like godrays, anti aliasing, and lower view distances

your cpu is quite weak

 

Telwen

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they bloat wattage recommendations to cover bad power supplies like yours

you need to override tessellation to something like 8x, and turn off things like godrays, anti aliasing, and lower view distances

your cpu is quite weak

The tessellation override is for AMD GPU's as far as i know. On the 2 PC's i have that run Fallout4 the only thing i turned off is godrays since it makes it all messed up to look at around the edges of characters.

I'm otherwise happy with how the game looks like and don't feel like i need to change anything i cant change within the launcher.

I'm aware the CPU is old, that's not the question here. But thank you for pointing that out.



 

maxalge

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all older gpu benefit from lowering tessellation

also i pointed out your cpu, because sli would not be advisable with it

also currently sli is broken in fallout 4