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 Post subject: Use overpowerd PSU due to better efficiency?
PostPosted: Wed Oct 23, 2013 12:11 am 
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Joined: Mon Oct 14, 2013 4:40 am
Posts: 6
Hi,

i am looking for a new power supply for my storage server - since it's on 24/7 it should be as efficient as possible.
I ended up with an Intel board an an E31230v3 as the Avoton based boards are still in low supply around here.

So doing the math:
Board + Processor + Ram + Raid Cards will likely be < 100 Watts (more like 40 on idle i hope)
Disks - Up to 16 -> max 160W, lets say 200 to be sure (load), max half of that on idle
So basically i need a high efficient power supply with max 300W on 100% load (and o/c the required Amperes for the 12V rail)

Now the other side - 40W + 100W =~150W idle, rather less since i probably wont use that many disks all the time.

I quote the power supply fundamental post here;)
"
Even so, Is Higher Power Better?

Without getting into technical details, the nature of a switching power supply is that it delivers as much power as is demanded by the components. This means that when installed in a PC whose components require 200W, a 400W PSU and a 250W PSU will each deliver 200W. Does this mean the 400W is coasting while the 250W is struggling? Not if they are both rated honestly and if they have the same efficiency. If one has lower efficiency than the other, then it will consume more AC to deliver the same power to the components, and in the process, generate more heat within itself. As long as there is adequate power, higher efficiency is the key to cooler, quieter PSU operation.

The main benefit of higher power PSUs is when the airflow in the PSU is deliberately set very low in order to minimize noise. This usually means the PSU components will run hotter. If all other things are equal, a higher rated PSU may be a better choice in such an application because its parts are generally rated for higher current and heat than a lower rated model.
"

So am i right in thinking that to pick a proper power supply i need to look at my power usage and then select the PSU which can supply the desired wattage (range) with the highest efficiency even if is extremely overrated?

I am not taking the price into consideration i know, but i guess it wont be too much difference between a high efficiency 400W and a high efficiency 700W PSU since the masses tend to use higher wattage than needed.

So:
Is the price the only difference at the same efficiency level at my usage range?

Assuming i dont care about the price and i find a power supply with 1000W rating and efficiency of 93% at 10%+20% (100w/200W) is it more efficient than a PSU rated 400W with 92% at 10/20/50% (40W,80W,200W) ?
Or will i be mislead since i cant actually compare the real supplied wattage/efficiency levels (i.e. i cant compare them watt by watt since all i get is ranges, here i dont know the efficiency of the 1000W PSU at 4%,8 usage to compare that to the 400W)?

Thanks,
Thomas


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 Post subject: Re: Use overpowerd PSU due to better efficiency?
PostPosted: Wed Oct 23, 2013 7:45 am 
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Joined: Mon Oct 14, 2013 4:40 am
Posts: 6
I should note the server is gonna be a SuperMicro 836 so i'm afraid (aside from the general discussion) i wont be able to use an ATX power supply for it :(
Which probably will limit my choices severely.


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 Post subject: Re: Use overpowerd PSU due to better efficiency?
PostPosted: Wed Oct 23, 2013 8:23 am 
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Joined: Fri Dec 27, 2002 1:49 pm
Posts: 834
Location: Somerset, WI - USA
Which version of the 836? Some have 80+ Platinum PSUs. But yes, you will be limited to using Super Micro power supplies only.

As for you more general question, if you want to get the most efficiency possible, you have to match the PSU to your power requirements. Which is difficult unless you can test the exact efficiency curve of each PSU you are looking at. I made a quick graph of some of SPCR's PSU reviews which you can see in my PSU Efficiency Comparison. I just picked out a few PSUs, primarily Seasonic and then also some high and lower wattage models. Where you see a difference between the higher wattage and lower wattage models in general is below 200W. Up to 100W, the low wattage PSUs have a good advantage over the high wattage ones. By 200W, things are pretty even. Above 200W, the higher wattage PSUs generally have the advantage. Of course the Cooler Master shows that the wattage itself doesn't automatically mean anything as it is below every PSU at every wattage.

But given your setup, you probably will never be below 100W. So really, the difference between a 300W and 1000W PSU won't be much. Either one would work fine. And while having headroom is good, I wouldn't expect a good quality 300W PSU running at 250W to have any more issues or a shorter lifespan than a 1000W PSU at the same load. And you won't have that choice as you'll be limited to the SuperMicro PSUs. I would go with the 80+ Platinum if you can. I would assume this thing will be running 24/7 as well. Note that these PSUs run at all times when plugged in. Even if the server is off. So they're not good for a system that will be sleeping or turned off often. Which you wouldn't expect in a server.


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 Post subject: Re: Use overpowerd PSU due to better efficiency?
PostPosted: Wed Oct 23, 2013 9:42 am 
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Joined: Mon Mar 17, 2008 1:49 pm
Posts: 1192
Location: UK
I would use a smaller PSU. High power efficiency is far better than lower power efficiency plus your capital spend will be far smaller.

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 Post subject: Re: Use overpowerd PSU due to better efficiency?
PostPosted: Wed Oct 23, 2013 11:14 am 
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Joined: Mon Oct 14, 2013 4:40 am
Posts: 6
BillyBuerger wrote:
Which version of the 836? Some have 80+ Platinum PSUs. But yes, you will be limited to using Super Micro power supplies only.


Well its a used one, an older revision with an 800w PSU; i couldn't find the one mentioned in the manual at Ecova at all, so its probably <80%.
I will check whether the one actually built in is the same or not but i doubt its a good one...
I would look at either replacing the PSU with ahigh efficiency SM one (PWS-501P-1R7) or if i could find it anywhere the Titanium level PWS-1K29P-1R - which likely costs more than i'd be willing to pay;)

On the other hand, even if its a server its for home use, so if all else fails i could leave the case open and go for an ATX anyway;
a lower wattage PSU (400) would cover the low efficiency <20% hole most of them still seems to have...


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