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I have this power supply : OCZ Z series gold 850w
http://www.ocztechnology.com/images/awards/Z850_chart.jpg

Can I really use the full 850 watts from the 12 volts continuously or I'm asking for trouble?

What is the maximum power I should use if I want to be on the safe side and lowering the chance of breaking it?

Typically, 80-90% of max is recommended for 24/7 usage. I go by the rule of thumb that you take the PSU's efficiency into account. For an 80Plus PSU that's only 80% efficient, I'd say 80% of it's max load. For your 80Plus Gold, which should be 90% efficient, I'd say you can go to 90% of the max load.

Brand also comes into account, but I think those OCZ ones are good.

I've heard 85% is a safe number for 24/7. Just make sure it stays cooled, or it's going to blow.

Power ratings usually come from the available heat dissipation from the switching regulator heatsinks. But that is usually not the problem if the environment stays cool.
The problem are the quality of the built-in fans which are, in almost any case crap.

Ironically if you want to go for reliability it is best to buy a "silent" power supply because those have good fans without you changing the fan and loosing the warranty.
A failure doesn't require the fan to fully fail, just a hickup and under full load the thing will be toast.

That's why I said efficiency is a key factor in determining how high you can run a PSU. The difference in a 1200W PSU between 80% efficient and 90% efficient is > 100W. That's a lot of extra heat inside a PSU. When dealing with a 850W unit (like the OP has) thats 90% efficient (Gold) vs one that's 85% efficient (Bronze), the difference is still 40W. Having the PSU output that extra 50% more heat makes a difference in how much you can run off this 24/7.

It's 80Plus Gold, it's 88% efficient @ 100% load. So it will dissipate 116Watts at max load. It's almost as much a vanilla 80Plus 650W PSU.
Make sure the PSU is well vented at max load, and use a P3 Killawatt to meter the input load, and never exceed 966Watts.

I personally like to keep a 25% margin or 200 watts.

Seems to work,cause when I don't,it bites me in the butt  :-[

Like others have said, if you're looking at anything over 750 watts constantly, upgrade. Go 1200W then you don't need to worry for a while. Only time I'd run at 850 is if I had ordered the other stuff and it was on the way.

Really? Yes, a 850W PSU that's 88% efficient will pull 966W from the wall at 100%, but he's asking what % he can run at for 24/7 use. You're not going to run ur PSU at 100% for very long. If you're using a kill-a-watt, try to keep the at-the-wall readings below the rated max, in this case 850W.

Some of the PSU reviewers have torture tests, where they put their PSU's in an oven at 50C or some such and load them at 100% for hours. It can be done, but Murphy's law will likely kick your ass. You'd get away with it just "benchmarking", soon as you tried to do something you really needed or wanted to do, it'd cough sparks an hour in.

Depends on the PSU and your rig setup..


I managed to mine successfully with 4 5800 series cards on a Antec 620watt PSU.


be careful with PSU's with multiple 12volt rails..

Thanks all for your input. I will use my killawatt and try to stay below 80% of the maximum output.

Double it!!!!
I.E stay BELOW 50% and have a happy life.


1. Every 10 degrees above 25 degree cent  HALFS the life of electronics.
2. Some days are hotter.
3. Sometimes the device will issue a sudden peak demand on the PSU, the closer you run to the maximum rating the more negative the effect on the internal semiconductors. (ripple increases the more you load towards the max)
4. it is a switched mode power supply, they automatically adjust for the power output required, it is not an iron cored transformer power sucker.

HC

so you will buy a 1200watt PSU instead of a 750watt for fun?  Mining rigs usually only consist of GPU's and a hard drive.

a quality 750watt PSU with 60+ amps on a single 12volt rail will go a long way when you're only running GPU's.


I thought we were here to make money. :)

Try to run 5 x 7970's...  i use 2 SeaSonic 750's on one rig. 

Althouth, haveing them clocked at   930/780/0.937, they only pull about 850w at the wall.

Well you could get away with a quality 850watter with a max output of 900+ watts.


Quality PSU's are underrated and usually have a higher max output on the 12volt rail.

Powering TEN GPU's plus a motherboard/cpu/ram/hard drivefrom a rosewill 1300W lightning all day long, and 6 from a 750W NZXT HALE90. Pretty much all my power supplies are maxxed and are trucking along all day long.

I agree i underuse my SeaSonics.  I started getting the 650's, cause at least they still have 2 sets of pci wires.. i HATE molex adapters

Me too. I don't mind the single plug ones you get with some of the 7900 series cards, nice and long with a single plug :)

http://www.urbandictionary.com/define.php?term=twss

TWSS but why so thin?

Sounds like a personal problem.

http://slickdeals.net/f/5382666-Antec-Truepower-Quattro-OC-1200W-80-Plus-Silver-Modular-Power-Supply-109-99-with-free-shipping-NCIX

speaking of psus...  dont know how good it is, but i picked up a couple to have around

ewww multiple 12v rails :P

6 Rails, but they're 38A apiece. I don't see anything wrong with that.

Any PSU I have used with multiple rails has caused me problems.. or died...

Just bad personal experience I guess.

my rationalization is:   I can buy 4 sets of 'powered' pci cables for 100bucks.

You really do not want a multi rail power supply, unless it is crowbar protected or VERY expensively designed.
If one of the rails goes down, then your very expensive hardware is toast as the other rails suddenly become biased against the missing rail.

in the case of a -12 +12 , it can become +/- 24v locally in the hardware ,but still look like +/- 12v to the external circuit regulator!!!!

I have a multi rail 1000 watt here and it works.. Turns on.... if you use a certain pci-e cable it shuts off...

if I use it for normal PC use it's fine.....