To put wattage needs in perspective

trents · Apr 18, 2015

I checked the power draw at the wall on my system which includes one Radeon 280X, a 4790k overclocked to 4.7 ghz, 16 gb of RAM, water cooling pump, seven fans, an SSD and a spinner. When running 3DMark the TPD never reached 350 watts. I have a 750 watt PSU and was wondering if I could cover another Radeon 280x which is rated for 250W TDP. So the PSU should easily cover it as that would make a total system TDP of 600W under full load.

Thought I'd share this for those confused about how big a PSU they actually need. Assuming you are talking about quality constructed PSUs whose wattage ratings are not exaggerated, it's probably not as much as you think.

Spending $15 or so on a watt meter is also a good investment.

Dlaw · Apr 18, 2015

Good advice Trents. And also keep in mind that the 280x pulls more power than anything in the current generation of Nvidia cards, bar the Titan X. I'm pretty sure my Supernova is overkill for my build.

Mandrake4565 · Apr 18, 2015

trents said:
I checked the power draw at the wall on my system which includes one Radeon 280X, a 4790k overclocked to 4.7 ghz, 16 gb of RAM, water cooling pump, seven fans, an SSD and a spinner. When running 3DMark the TPD never reached 350 watts. I have a 750 watt PSU and was wondering if I could cover another Radeon 280x which is rated for 250W TDP. So the PSU should easily cover that as that would make a total system TDP of 600W under full load.

Thought I'd share this for those confused about how big a PSU they actually need. Assuming you are talking about quality constructed PSUs whose wattage ratings are not exaggerated, it's probably not as much as you think.

Spending $15 or so on a watt meter is also a good investment.

Good idea for the post Mr T. Most people do go way overkill when buying a Psu, especially when running an Intel Cpu. I actually had a Watt Meter on my 4770k the other day while benching my GTX 580. With the Cpu at 5.0 1.525 V and the 580 maxed out on what Afterburner would give it voltage wise. I was still only at 520w draw from the wall. Taking into account this is an extreme example and the GTX 580 is a monster power consumer when pushed. I agree with you one could easily run X Fire/Sli with a 750w Psu and even be able to get away with a 650w if the overclocks are within reason.

trents · Apr 18, 2015

Good point about the CPU, Manny, whether it be an Intel or an AMD. The top drawer AMD CPUs when heavily overclocked will probably draw as much wattage as a 280X . So that would need to be taken into consideration.

EarthDog · Apr 18, 2015

I assume this is with the clocks of your system in sig? Stock??

nice to see more support!

Now, if you had an amd octo.... different story.

To give more support. I run my 5820k @4.2ghz, 1.25v and a 295x2 stock on a 750 psu. I don't break 550w when gaming. Now, when I push to 4.7+ and overclock the gpu to it's benching limit, I can hit 750w actual. Most won't do that though.

bob4933 · Apr 18, 2015

Is a kill-a-watt fast/accurate enough for peak voltages?

EarthDog · Apr 18, 2015

It's close and fast enough for our purposes, yes. You just have to take into account psu efficiency into the equation.

(As an aside, I listed actual wattage after psu efficiency in my post)

Mandrake4565 · Apr 18, 2015

trents said:
Good point about the CPU, Manny, whether it be an Intel or an AMD. The top drawer AMD CPUs when heavily overclocked will probably draw as much wattage as a 280X . So that would need to be taken into consideration.

It's a big difference when really pushing the Fx 8xxx Mr T. with the same GTX 580 maxed out and with my 8350 @ 52xx Mhz I've seen 700+ watts drawn from the wall on some 3D benches. I did an extreme test once running both Heaven and Prime 95 at my 5.1 stable Oc on the 8350 with the GTX 580 and saw this, 827 w from the wall :shock:

Obviously this is not a normal scenario

trents · Apr 18, 2015

I outlined the OC parameters and components in the fist post, ED.

- - - Updated - - -

Manny, looks like you need a new watt meter. The "2" is only half there.

EarthDog · Apr 18, 2015

Sorry, got it... was lost in a sea of TDP in the first post!

Audioaficionado · Apr 18, 2015

I have a kill-a-watt meter buried somewhere in all my piles of PC junk. I'm running two AMD 7870 cards flat out with GPU_FAH 24/7, but Q6600 CPU isn't under much load all under a PCP&C 610 Watt PS. It seems to be more than enough power. Now if I tried to run the CPU fully loaded too, it might push the PS to the limits. I think the quality of the PS is the difference.

Silver_Pharaoh · Apr 18, 2015

Audioaficionado said:
I think the quality of the PS is the difference.

QFT!

Never cheap out on PSU's. Just asking for trouble.

We ought to put that as a banner message on the top of the page

NiHaoMike · Apr 18, 2015

You can get cheap and good if you know where to look. The surplus HP server PSUs are really popular with hobbyists looking for 12V at a high current, most notably R/C hobbyists.
http://www.overclockers.com/forums/showthread.php/758275-Inside-a-HP-12V-100A-1U-PSU
Only catch is that you will have to do some DIY wiring, but it's all low voltage and easily done by anyone with some experience in electronics. Probably the easiest is to use a normal PSU (good quality but small) for the motherboard and drives, then dedicate the server PSU to the GPUs. Use a relay from the regular PSU to turn on the server PSU.

Mandrake4565 · Apr 18, 2015

trents said:
I outlined the OC parameters and components in the fist post, ED.

- - - Updated - - -

Manny, looks like you need a new watt meter. The "2" is only half there.

It's just the angle I took the picture from.

EarthDog · Apr 18, 2015

Audioaficionado said:
I have a kill-a-watt meter buried somewhere in all my piles of PC junk. I'm running two AMD 7870 cards flat out with GPU_FAH 24/7, but Q6600 CPU isn't under much load all under a PCP&C 610 Watt PS. It seems to be more than enough power. Now if I tried to run the CPU fully loaded too, it might push the PS to the limits. I think the quality of the PS is the difference.

It is more than enough. Stock 7870s are 175w cards. You could easily add the cpu in there as well and even overclock a bit.

People tend to overestimate quite a bit on how much they really need.

Mandrake4565 · Apr 18, 2015

EarthDog said:
People tend to overestimate quite a bit on how much they really need.

to that ED

petteyg359 · Apr 18, 2015

EarthDog said:
People tend to overestimate quite a bit on how much they really need.

Well, nobody makes a 600 W 80+ Titanium yet, so that AX1500i has slightly better efficiency even at my idle 320-ish watts than a Platinum at almost-full-load 500W

Now I just need to get a 230v circuit into the computer room to eke out that last 1%

Janus67 · Apr 18, 2015

Too bad under almost all circumstances the cost benefit for the extra efficient model is lost based on the power savings versus the price premium.

petteyg359 · Apr 18, 2015

Janus67 said:
Too bad under almost all circumstances the cost benefit for the extra efficient model is lost based on the power savings versus the price premium.

And that is why we have a world that doesn't give a **** about the world - because it's all about the immediate price in dollars. But, for an older system with a < 90% efficient PSU, it will pay for itself within the warranty period unless you have a below-average per-kWh price.

caddi daddi · Apr 18, 2015

Janus67 said:
Too bad under almost all circumstances the cost benefit for the extra efficient model is lost based on the power savings versus the price premium.

it's not all about the cost, some of us, me, buy the better units to keep things quieter, more efficient psu, lower fan noise and less heat to get rid of being put into the case.
reading oklahoma wolfs reviews the trend i see is that most psu's behave the best at around 50% output, so that is my target when psu shopping, I don't have all his cool test gear so I buy his, if he'll ship to me.

To put wattage needs in perspective

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