oc'd e6600 and 8800GTX powered from 380W PSU - why not?

Theoretically , why can't the system bellow be ran from a 380W PSU?

First, the system:

1. 8800GTX alone = 132W full load, 70W idle.

2. e6600 @ 3.6GHz with 1.47v vcore actual = 135W @ 100% utilization.

source: http://www.extreme.outervision.com/psucalculatorlite.jsp

3. 4x1GB DDR2 RAM.

4. 2xSATA 7200RPM HHD and DVD burner.

5. P5W64 WS Pro motherboard.

6. 4 pretty low-power fans, including yate-loon slow inside the tuniq and whatever is inside of the 8800GTX.

7. misc. extension cards that come and go

8. PCP&C 750W Silencer


1 and 2 are the biggest draw of power, 3 to 7 really don't consume all that much. CPU and the video card then are the parts to worry about.



How much power does the whole system use? According to the Kill-A-Watt gadget from P3 International, PSU draws form the wall (I am rounding up):

At idle:

250W with 2A

Running CSS video test (I tried to spice things up by running orthos at the same time but the load didn't change):

380W with 3.2A

The 750W Silencer hits 80+ efficiency above 150W and keeps it till 600W load according to this review:

http://www.pcper.com/article.php?aid=374&type=expert&pid=5

Round up the efficiency to 80% and that will give us:

380W/5*4=304W of real power being consumed by the system under full load.

Give it a bit of a buffer to stay on the safe side and it looks like all I need is a 380W PSU for that system.


So, lets pick a modern 380W PSU:

http://www.newegg.com/Product/Product.aspx?Item=N82E16817371005

let's see now. 2x12v rails, each at 17A.

the juice the components need to run at full load:


8800GTX - 132W/12V=11A

e6600 @ 3.6GHz - 135/12v=11.25A


Seems to be plenty left for whatever the rest of the system needs.

The PSU is rated to draw up to 6A form the wall. All my system needs is 3.2A at full load. So we seem to be safe there as well.


OK now, am I making a mistake somewhere? Or tell me some other reason why the system above cannot be ran from a 380W PSU .

They don't make 50 amp 380W PSU's. You also always want some overhead.

* *

as i've shown, there's enough overhead; you don't need 50A for that system.

mcoleg said:

as i've shown, there's enough overhead; you don't need 50A for that system.

Click to expand...

Sure it will run but not well and you risk all your hardware when it goes up in smoke. So as Clint said best "Do you feel Lucky?".

well, the numbers hold. show me where i am wrong.

no, really, i'd like to know 'cause it does seem pretty surprising.

I'd suggest heading over to JonnyGuru and doing some reading. When you start to stress a PSU the power it delivers can be less than clean - the power signal gets fluctuation called "ripple" which can be hard on your components. Many less expensive PSUs won't run for too long at or above their design limit. That 350W PSU may do fine. But for a few extra bucks I'd prefer to get some cheap insurance for the rest of my system.

it wont work with that psu because the numbers are misleading. 2x17A@12v=404 watts. its a 350 watt PSU. number play in effect.

380 watt power supply

The Jizzler is right!
If you add up all the amperage on all the rails, you might think you have 596.1watts of power which there is no way thats going to happen on a 380 watt power supply.

What the amperage on the rails means, is you might get 17 amps on either of the 12 volt rails, and 20 amps on the 3.3 volt rail, and 20 amps on the 5 volt rail as long as the total isn't over 380watts which I doubt it could supply even that for very long.

It's to bad the numbers are so misleading and that's with a good name brand power supply, a lesser grade power supply won't even do on any rail what they advertise.

I have tested personally quite a few cheap supplys with digital meters and they almost never put out on any rail what they advertise let alone all rails.

good point, Jizzler. their 380, 430 and 500 models appear to have same specs except for the amperage they can take from the wall.

Rip, i've read whatever there was to read there and lots of other palces as well. thanks for the suggestion though.

That system probably would run fine on that PSU, because the Earthwatts are Seasonic made PSUs that actually put out their advertised wattage. Check out this review of the 430W one where it is able to push 13W on each 12V rail (each is rated for 17 apeice, but combined +12V rail is lower).

http://www.silentpcreview.com/article684-page4.html

I think the overcompensation on PSU wattage stems from people's experience with the mostly shoddy PSU manufacturers who greatly overstated the PSU's capacity.

People have run overclocked Quad Core CPUs with dual 8800GTXs in SLI on the Corsair 620W and it performed like a champ. The system as you described should run on a high quality 380-400W psu just fine.

In theory everything should be fine. But practically, there are a couple of issues at hand. You have heavily cross-loaded the PSU and most PSU's won't hold up well if cross-loaded in the long term. Next, you forget that the chipset is a major power hog as well. The chipset dissipates more heat and draws more power than your HDD's, all on the 12V. Therefore, running that rig on 380W unit is a strech for all practical purposes.

true but considering that the whole thing consumes only around 300W under load (i was convinced it should have been more, btw), which includes all the power consumption, chipset, ram, drives, etc., there is still a comfortable overhead left. the only real concern is the distribution on the 12v rails...

i am almost twitching to try it


no reason, really, just want to see if it's possible.

^^ crossloaded... meaning one rail loaded more than the others. a load imbalance across the rails?

mcoleg said:

true but considering that the whole thing consumes only around 300W under load (i was convinced it should have been more, btw), which includes all the power consumption, chipset, ram, drives, etc., there is still a comfortable overhead left. the only real concern is the distribution on the 12v rails...

no reason, really, just want to see if it's possible.

Click to expand...

There's one way to prove you are right: do it! Sure beats theory.

The system will boot and you can surf the web and chat on AIM. But, in the past, many people came back asking for help because their system would crash or ran very poorly with a low powered PSU; either when OC or gaming.

As well as, low powered PSU will fail very shortly, because it cant handle a high load for very long periods of time. They weren't designed to do so in the first place.
You need to have a PSU that will have room to spare and or, a PSU that is specifically designed from ground up to handle high loads for long long periods of time.

Many manufacturers will use cheap components on a low Wattage PSU and then use better components on a higher end PSU, and thus you pay for it more.

You just never want your PSU running right at the Edge all the time. Unless its specifically made for that purpose and has the internal components for it.

mcoleg said:

no reason, really, just want to see if it's possible.

Click to expand...

I'd buy a Zippy or an independantly regulating Sparkle for that experiment.

Zippy's can be found on myaopen.com

funnyperson1 said:

That system probably would run fine on that PSU, because the Earthwatts are Seasonic made PSUs that actually put out their advertised wattage. Check out this review of the 430W one where it is able to push 13W on each 12V rail (each is rated for 17 apeice, but combined +12V rail is lower).

http://www.silentpcreview.com/article684-page4.html

I think the overcompensation on PSU wattage stems from people's experience with the mostly shoddy PSU manufacturers who greatly overstated the PSU's capacity.

People have run overclocked Quad Core CPUs with dual 8800GTXs in SLI on the Corsair 620W and it performed like a champ. The system as you described should run on a high quality 380-400W psu just fine.

Click to expand...

I'm quoting the entire post because it bears repeating.

You can certainly run that rig on a quality 350-400W PSU as your numbers have shown. Any quality unit in that range should do fine, Enhance 400W (combined 12V rating of 336W), The seasonic built Antec earthwatts that was linked (324w combined 12V rating), Enermax Liberty 400W (360W combined 12v rating) would all be good examples. Or like Supernade suggested, forgo getting a desktop grade unit and just pick up an independently regulated server grade Zippy or the like, that you know is fully capable at running at its rated load 24/7.

All comes back to the quality of the PSU you are using. Sure there are plenty of units that would have horrible voltage regulation under that load and not output a clean signal but you don't find that kind of junk being recommended around here, at least not last time I checked.

If it would make everyone feel better I could power down my main rig and throw my Antec earthwatts 380W unit in it.

E6600 @ 3.2 (1.4375 V) yeah its a B2 stepping week 24, it was never all that good to me.
x1900 xt
4 HD drives + an optical
2 x 1 GB memory
4 Case fans
X-fi
Ati theater 550 TV tuner

Not exactly my plan for the night but if it helps combat power supply related FUD...

Alexhk, i have one coming in . we'll see how it will do.

Alex if you can post a few pics and perhaps let it run a benchmark overnight, I'll sticky your thread.

mcoleg, which unit did you buy? Hope it isn't a Powmax..lol

the one i linked from newegg in my first post - seasonic-made antec.