PSU Upgrade for GPU on a basic PC.

[craigo5000]

Hi all,

System spec is as follows:
HP P6740uk running 64bit Window 7.
Processor: AMD Athlon II X4 640, 3000Mhz (4 cores)
8GB of RAM (2 x 4GB)
1 x 1TB HDD
1 x CDRW
1 x Multicard reader
OEM PSU is a Deltec 300W max unit (Continuous power is rated lower)

It had a Geforce 405 card which was weak. Having read the requirements for a stock GTX 750Ti, I went and bought the small EVGA OC version (no 6-pin so all power drawn from the PCIe slot 75w Max). After purchase the EVGA instructions stated 400W and 20A on the 12v rail. (Too late!) My stock PSU is 300W max and only 18A on the 12v rail BUT, there's not much else in the machine drawing crazy power demands.

The machine copes well and I've stressed it for weeks now using Heaven Benchmark and get a nice 55FPS on high - super stable. I've also played games for hours on end with great results and overall I'm happy.

This makes me think that the manufacturers do over-stipulate the PSU requirements. Obviously Deltec make some nice OEM PSU's and I can understand companies like NVidia may over-estimate to give the user huge headroom on weak PSU's on the market that aren't capable of sustaining stable continuous power at high loads.

ANYWAY.....

I may be able to get hold of GTX 780 and so wanted to get a more powerful PSU.
Would the EVGA 500W 80+ Bronze be fine to use seeing as my CPU and other accessories are relatively low power?
http://www.evga.com/Products/Product.aspx?pn=100-W1-0500-KR

The GTX 780 spec states 42A and 600W minimum but there's not a chance in the world that card draws probably even half of that much demand on it's own.

There is a video on YouTube with a guy demoing a Corsair 450w with an even more capable Ti version the GTX 780 on an i5 with an SSD, 2 x HDD and loads of fans and stressing it along with all his other components was drawing 400W from the wall MAX. I would take an educated guess that my system would draw a mere 350W max from the wall - probably less. Take into account the loss of 20% efficiency at the PSU and that puts me at 420W max.

Any thoughts welcome.

 

[madmatt30]

The evga would run it but to be honest your old athlon would seriously seriously impair performance - I dislike the word bottleneck personally but in this case that's exactly what you would have
You want to be looking at a CPU/mb major upgrade before splashing out big money on a high powered GPU.

 

[craigo5000]

That's good to know regarding the PSU. Thanks

The only game this rig is built for is an extremely intensive GPU online game that I've monitored CPU for. Once loaded up, it barely touches 40% on all 4 cores. Does that indicate my CPU is doing okay under these circumstances?

Thanks

 

[sleepwalkerfx]

You are correct. I believe VGA card manufacturers estimates the PSU wattage considering the worst case scenario where you might have many components such as water cooling or custom cpu coolers, extra fans, many hard drives, and other external devices plugged in etc. In your case your other hardware draws very low power so 300W for a GTX 750Ti should be enough.

In fact, Nvidia suggests 300W PSU for a GTX 750Ti (http://www.geforce.com/hardware/desktop-gpus/geforce-gtx-750-ti/specifications)

And your card draws 68W at it's max load (http://www.tomshardware.com/reviews/geforce-gtx-750-ti-review,3750-21.html)


As per this PSU calculator ( http://www.extreme.outervision.com/PSUEngine ) your system will be drawing 271W when system's all components at 100% load (all components at 100% is extremely unrealistic though). A 90% load will only draw 235W.

So if your PSU is a solid brand which actually outputs 300W (unlike some cheap brands which doesn't always outputs the mentioned wattage) then you have nothing to worry about.


With a GTX 780 your system will be drawing 450W at your systems max load (including CPU at 100% and GPU at 100% and ALL other components are at 100% load. This is never going to happen anyway ) And, at 90% load it will only use 398 W. Which means a true 500W PSU will be more than enough.

 

[sleepwalkerfx]

That's good to know regarding the PSU. Thanks

The only game this rig is built for is an extremely intensive GPU online game that I've monitored CPU for. Once loaded up, it barely touches 40% on all 4 cores. Does that indicate my CPU is doing okay under these circumstances?

Thanks

I don't think your CPU will bottleneck a GTX 750i or a GTX 780. With a CPU intensive application when your CPU touches 100% you know it's time to upgrade it. But it's unlikely to happen something like that any sooner.

 

[craigo5000]

That's all reassuring to read. Thank you for taking the time to post.

Indeed, I researched the GTX750ti before buying and saw NVidia recommended a 300W PSU. Only then did EVGA's Overclocked version recommend an ever higher spec PSU on the box just as I'm about to install it! There's only 75W max available from the PCIe slot anyway as this card has no 6/8pin connection. Clearly, all is well with it running on my system but this does annoy me why manufacturers don't just say what the card actually requires.

I'll keep an eye on CPU/RAM activity too. RAM is never over 3GB and CPU for this online game is never over 40%. As mentioned, I guess a mobo/CPU upgrade may be on the horizon if I was to play something more CPU intensive, but for now the EVGA with it's 500w continuous supply at 40degC sounds like it's safe to go ahead with.

Thanks again for the replies.
Thanks

 

[craigo5000]

Just to add to this. I've now bought and installed said PSU and hammered away with bench test programs on both the 750Ti and 780. The 750Ti certainly holds it's own and is so cool and quiet in comparison. Averaging just over 52FPS at high resolutions at only 65degC max. The 780 scored me 90FPS and started to thermally restrict processing power once it reached 80degC. I didn't really hammer on much beyond that. I've since gone back to my 750Ti as the noise from the 780 was crazy. Almost like a vacuum cleaner when pushed hard!