Max power out of a Dell Z750p / N750p Power Supply?

[thedreamer]

As title asks, what is the max people have gotten away with using these power supplies?


I run then just around 700watts and they are tanks. IMO one of the best bangs for the buck, but once for about an hour, I didn't realize that it was running at 880W.
Nothing happened, the SP20 was happily hashing away, it wasn't even warm to the touch, but just wondering.

Thanks

[sidehack]

I had no trouble pushing a pair of overclocked S1s off a PSU for a couple months. When I was overcurrent-testing, I saw trips anywhere from 75 to 80A output depending on the specific model. 75A at 12V is 900W so you were probably pretty close to the PSU dropping out.

[Prelude]

What sidehack said.

You didn't harm it, server PSUs are built like tanks. Where did you get your reading for 880w? At the wall? If so, that's not the PSU's output in DC watts, there's an efficiency loss to factor in.

[thedreamer]

Yeah that was on a Kill-a-watt.

So if I run them for a bit sometimes at past 800watts it's still ok?

What about running an EVGA 850W G2 at right the 850-900 watt limit? Is that ok? I know the 1300 G2's are fracking tanks, but just thought I'd ask. 

[Prelude]

Yeah that was on a Kill-a-watt.

So if I run them for a bit sometimes at past 800watts it's still ok?

What about running an EVGA 850W G2 at right the 850-900 watt limit? Is that ok? I know the 1300 G2's are fracking tanks, but just thought I'd ask.  

Absolutely fine. I'm not familiar with your particular PSU model, so I'll assume 90% gold efficiency running on 240v (figure 88% if using 120v):

880w * 0.90 = 792w being used by your hardware
800w * 0.90 = 720w being used by your hardware

You could run either calculation 24/7 without issue.

For the EVGA:

900w * 0.90 = 810w being used by your hardware (240v input)
900w * 0.88 = 792w being used by your hardware (120v input)

I'd be fine with running the EVGA full blast at 850w (965w at the wall on 120v)

Edit: Just realized you're using 120v if you measured with a Kill-a-watt. Ignore my 240v numbers.

[thedreamer]

Ohh.. so if the kill-a-watt says 800Watts, it's only really using 720watts out of the power supply?

So the real limits on an 850Watt EVGA SUperNova G2 is about 930+- watts at the wall?


This is all expecting a 90% efficiency PS.

[Prelude]

Here's a review for your EVGA: http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story3&reid=377

Jonnyguru is the reference when it comes to PSU reviews.

The important information:



What you want to pay attention to is Test #CL2. That's a test which maxes out the 12v rail, without any use of 3.3v or 5v, and that's what mining represents.

You can see that while pulling 837.9w of DC power from the PSU, the PSU its self was pull 963.4w of AC power from the wall. That gives the PSU an efficiency rating at almost (he usually maxes them out, not sure why he didn't reach 850w in this review) full 12v load of 87% with 117.9v of input. He's running off of a 20A outlet, so if you're using a 15A outlet you can expect slightly lower voltage. I'd guess about 115.5v.

Using the 87% figure, we can calculate that

850w / 0.87% = 977w measured at the wall. That's what you want to stay under, 977w. I only recommend running 100% load with top quality units, which your EVGA is. Lesser PSUs will croak. If Super Flower (The OEM of your PSU), Seasonic, Flextronics, Delta, etc made your PSU, it's capable of running full out 24/7 for the duration of it's warranty period. Full out actually decreases as time goes by, but that's another subject for another time. Average PSUs I wouldn't want to run over 80% capacity 24/7, cheap PSUs about 70% and no name trash will be lucky to run at 50% for a few hours.

The higher your input voltage to the PSU is, the better your efficiency will be. As a rule of thumb, you can expect about 2% better efficiency at 240v VS 120v. That would mean you'd pull 944.4w at the wall under full load. 240v will also increase your PSU's life expectancy.

Take a look at this chart:



I know it says 240v is only a 1% increase over 120v, but in my experience 2% is more realistic.

And take the time to read the review I linked. You'll earn some good info about your PSU, and PSUs in general.

[philipma1957]

I have used the  evga line of g2's  they prefer just under the watts listed  if you are using a kwatt at the wall.

the 1300 g2   will do 1320 on a kwatt meter    but after 30-60 days gets spotty.  It will   do 1230  for months on end.

the 1000 g2   will top out at 1010 or 1020   but after 1 or 2 months not work as well.  It will do 970 for months on end.

the 850 g2   will top out at 875 or 880   but after 1 or 2 months not work as well. It will do 820 for months on end.

Prelude shows the Jonny guru  review on it. Notice when maxed it dropped under 12 volts. I try to run my evga's 5% -10% under the number it says

 1300  at 1170 on the  kwatt
 1000  at 900  on the kwatt
   850  at 800 on the kwatt

I have never melted or broken and evga psus running with this method.

As for server psus.  I am doing a review on three of them along with the included breakout boards.

I am testing the HP 1000 model but it is rated for 850 at 120 volts. It can do 1200 watts for 5 minutes then it turns off. (I thought It was the 1200 watt model)
So running it 1200/850 rating and no damage it just powered off.

https://bitcointalk.org/index.php?topic=985163.0  this is a review of the server.

[thedreamer]

Wow nice. So on my Dell Z750P and the EVGA 850 G2's, I have plenty of 'wiggleroom' if I need to.
I don't use it per say, but good to know, I can trust them at those levels.

*although the server PSU's are used, so who knows how much mileage they have to begin with.*

Thank You both.. Again.