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Author Topic: Dual PSU Woes - 3GH/s w/ 3x5970 + 2x5870  (Read 7413 times)
jjiimm_64
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February 15, 2012, 09:36:54 PM
 #21


the 60 number is an for older, cheap PSUs


if your going to mine. buy a very good PSU, it will pay for itself.

the seasonics advertise they're continuous wattage.

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cuz0882
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February 15, 2012, 11:23:06 PM
 #22

No, its for all of them. They all have efficiency charts, go look at them. Peak is not continuous. Even the nice ones should not be run at full capacity. Here http://www.silverstonetek.com/techtalk_cont.php?area=en&tid=wh10_005
jake262144
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February 16, 2012, 12:21:45 AM
 #23

No, its for all of them. They all have efficiency charts, go look at them. Peak is not continuous. Even the nice ones should not be run at full capacity. Here http://www.silverstonetek.com/techtalk_cont.php?area=en&tid=wh10_005

The 80Plus-imposed 20-50-100% efficiency curve is well known.

Please note that you're crying wolf over an efficiency decrease of 3 to 4% whilst at the same time you need to spend a great deal more money on powerful PSUs trying to keep the load at ±50%.
Try doing that with a huge mining farm, like the one Gigavps has... good luck.

Note that the scale Silverstone are using begins at 79% efficiency and ends at 91% to make the curve look more dramatic than it actually is.


Also, don't forget that the internal temperature increase of any PSU is inversely proportional to its efficiency.
A high-efficiency PSU will generate less heat, thus can be run at high load levels without incurring the temperature-caused MTBF degradation.
Start with a gold-certified PSU and you really can disregard that 2% efficiency loss when running it a 80%.

At 100% load, a gold-certified PSU may waste no more than 12% energy. For a 1000W unit that translates to up to 120W of heat - this really isn't beyond a 140mm fan's ability to dissipate.
Silverstone emphasize low fan speeds (and hence low noise) - this is completely orthogonal to mining as you won't hear the PSU fan with all the howling GPU turbines anyway.


I also have strong reservations about the temperature chart, I don't like it starting at 40°C. Any PSU drawing air from outside of the case will draw much colder air than that.
During this load test of a Silverstone PSU, delta between the intake and exhaust temperatures is just 16°C at 100% load. You can rest assured the innards aren't boiling at 70°C as Silverstone's article would suggest.
I can't agree with the claim that "components are rated at 85°C", this day and age 105°C rated components are being used in high-quality PSUs, including the said 1000W Silverstone one.


At best, the article you linked to suggests that Silverstone PSUs aren't necessarily the best choice for mining due to the emphasis on low-noise, low-speed fans and use of only 85°C rated components.
At worst, it can be regarded purely as propaganda: "Why use a 1500W power supply?" Of course Silverstone prefer to sell you an oversized and overpriced 1500W unit where a much cheaper 1250 watter would suffice.
DeathAndTaxes
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February 16, 2012, 05:15:51 AM
 #24

No, its for all of them. They all have efficiency charts, go look at them. Peak is not continuous. Even the nice ones should not be run at full capacity. Here http://www.silverstonetek.com/techtalk_cont.php?area=en&tid=wh10_005

From the link you provided there is a 2% difference in efficiency between 50% load and 100% load.  2%.

On higher quality 80Plus-Gold units from good brands like Seasonic the difference is efficiency between 50% load and 85% load is <1%. 

The "50% rule" is seriously outdated by about 4 or 5 years.    Skip the Silverstone and get a Seasonic.  I have 7 running at 80% load 24/7 for 9 months now.  They are cool to the touch.
check_status
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February 16, 2012, 07:30:10 AM
 #25

Quote from: check_status
60% of the peak wattage rating or 60% of the continuous wattage rating?
I asked, not caring if the 60% is correct, but to see how cuz0882 is calculating that 60%, what is going into the equation. I wanted to see the process used.
Please use gozinta's. Cheesy
I have 7 running at 80% load 24/7 for 9 months now.  They are cool to the touch.
Are you running them at 80% of peak or 80% of the continuous wattage rating?

I purchased an OCZ ZT 750w, was going to purchase an AZZA 850w, reading around here changed my choice (DAT, Inaba, jimi).
The OCZ ZT has a continuous rating of 750w, can I draw 750w (12v*62A=744w) without worrying about potential issues?

If it is designed to run at 750w continuously how is that bad to run it at 744w?

Gozintas are cool. Cheesy

With a single 1200w continuous PSU:
1 @ 1500w@w = 12.5A @120v
1 @ 1500w@w =  6.81A @ 220v

Compare to 750w continuous PSU:
1 @ 930w@w = 7.75A @ 120v
1 @ 930w@w = 4.22A @ 220v

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I have to find my Tesla gozintas, you like those. Grin
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jake262144
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February 16, 2012, 09:37:38 AM
 #26

Forget peak rating.   Peak rating is meant as a safety valve against high transient loads.

You know why the 80% load is reasonable? To leave a buffer in case the cpu ever gets pegegd at 100% (CPUs consume power as well), the cards are ran at stock memory speed due to a misconfig, Windows must be installed and booted(1), or some other serious incident affecting the power usage. It also makes the life of your PSU a tad easier.


(1) just kidding, a bit of Windows-bashing is always in order Cheesy
jake262144
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February 16, 2012, 10:29:23 AM
 #27

The "50% rule" is seriously outdated by about 4 or 5 years...

Kindly allow me to elaborate on that:
Way back when we were all younger, life was easier: any PSU had discrete 12V, 5V, and 3.3V conversion circuitry.
A 300W PSU was considered a powerful, high-end unit. 5V was enough to feed a CPU. 5V was the primary rail of a PSU and had an evil twin: the -5V rail.
Any PSU could deliver up to X watts at the 12V rail, Y watts at 5V and Z watts at 3.3V rail, e.g. a 400 Watt unit being capable of 80W at 3.3V, 120W at 5V and 200W at 12V.
The load at any specific voltage rail was pre-determined by how powerful curcuitry had been installed.

Let's skip forward to 2012 - the dominant approach today is called DC-to-DC conversion.
For efficiency's sake the circuitry for transforming 220V(1) into lowly 3.3V or 5V has been ditched.
Instead those non-primary rails are being fed by the 12V circuitry and need only to regulate down from 12V.
Almost 100% (let's ignore the -12V and standby 5V rails) of the PSU's output is converted to 12V internally.
Success! - this gives you flexibilty previously unheard of: if you have a 650W DC-DC PSU, it doesn't matter whether your load pattern is 100W at 3.3, 130W at 5V and 400W at 12V or 630W(2) at the 12V rail as long as you don't trip the internal overcurrent protection.

Mind you, that it's still the end-user's responsibilty to double check the topology and rating of any PSU before integrating it into such an edge case as a mining rig sporting 4 double-GPU cards.

The "50% load" rule-of-thumb advocates sound as if they spent a couple of years in a deep, dark dungeon... at least I hope they got some serious experience points out of it Cheesy

Oh, and let me reiterate once more: disregard the peak rating(3).

Notes:
(1) I'm not being Euro-centric. The 110V input voltage is being raised to 220V by the active PFC circuit or by the voltage doubler.
     The reason why PSUs achieve a couple per cent higher efficiency when plugged into 220V is that one circuit less needs to be used.
(2) I didn't use 650W as max load to accommodate for the discrete -12V and 5V standby rails often included in the max rating by those damned bean counters.
     Guys, if you're marketing a 650W unit, let me draw that 650W at the USEFUL voltages without overloading the PSU, ok? 650W should mean 650W, not 636.36251W Angry
(3) Historically, the peak rating has been horribly abused to the dismay of many a user ending up with a dead PSU or even the whole machine.
     Huntkey PSUs were a blatant example: units with the overcurrent protection set at eg. 500W were being marketed as 500W units.
     Had the damned marketroids marketed them as 400W units which they clearly were many disasters could be averted.
DeathAndTaxes
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Gerald Davis


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February 16, 2012, 03:10:00 PM
 #28

Forget peak rating.   Peak rating is meant as a safety valve against high transient loads.

This.  Peak rating for ATX supplies is marketing nonsense to make the supply look better to uninformed consumers.  While there will be startup peaks they are relatively small (as a % of overall continual load).

Honestly don't even look at peak power to avoid it possibly influencing you subconsciously.  I wouldn't pay $0.01 more for a unit w/ "higher" peak power.  Computers are continual loads, mining even more so.


jake is also right on the "history".  In the dark ages of ATX spec the 5V rail was initially used to power CPUs.  As CPU became faster they had to operate at lower voltage to avoid a thermal loads that would melt steel.  So the 3.3V rail became more important.  As CPU became even faster, even 3.3V was too high of an operating voltage.  Rather than have a new voltage rail with each new CPU (2.2V, 2.0V, 1.8V, 1.5V, etc) the load on 12V rail was increased and the motherboard converted the voltage to whatever the CPU/northbridge/memory needed.  As power increased the ATX spec was changed 4 times.  First the ATX 20 pin connector was expanded to 24 pins, next a 4pin 12V MB connector was added and then later doubled to 8pin, and finally direct GPU power connectors 6pin and 8pin were added.  Overtime the % of load that was 12V in average PSU went from 20%, to 30% to 50%, to 70% and now is 80%+ even on NON-MINING RIGS.

Due to that designing PSU that did direct conversion from 120VAC/240VAC to 5VDC (and 3.3VDC) became very inefficient.  Also any time spent making 3.3V & 5V efficient was largely wasted since 70% to 90% of the load was on 12V rail.  This caused PSU designs to move to "rail to rail" conversion.  Since most of the load was 12V convert everything to 12VDC FIRST and do it was efficiently as possible.  Then convert some of the 12VDC as needed to 3.3V & 5V but honestly efficiency isn't important because at most a modern computer only has a token amount on 3.3V/5.0V rails.

Really the ATX spec should be overhauled.  Today there is no reason that a PSU couldn't be 100% ultra high efficiency 12VDC. Technically 18VDC or 24VDC would be even better but you would lose all backwards compatibility. So 12VDC is a reasonable compromise.

jake262144
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February 16, 2012, 03:42:33 PM
 #29

... While there will be startup peaks they are relatively small (as a % of overall continual load) ...
Roger that.
The startup peaks are insignificant - the real load begins once the OS boots up and the miners launch.
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