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Old 08-02-2012, 05:01 AM   #1
boran
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Default Influence on power supply on total power usage ?

Hi,

I am planning to construct a new allround server for at home.

One of my goals is low power usage, for this I am basing my build a bit on the HTPC build as presented in this article.

(with a 2120T instead of a 2100T due to availability)

Now I am wondering however how much influence my power supply has on the total power usage.


In that article he gets 22 watts at idle. I have a 380 Watt PSU lying around, will this influence my idle power usage ? Does PSU get less efficient at lower power usage ? Should I get a more specialized PSU of 150 watts for instance ?
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Old 08-02-2012, 07:23 AM   #2
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PSU efficiency is rated between 20% and 100% load according to 80Plus. Typically you see a pretty sharp drop in efficiency below 20%. A bronze rated unit, typically 82% efficient at 20% load, can drop to around 70% at 10% load.

A highly efficient low power PSU: PicoPSU 120W or PicoPSU 150W XT

It's really going to take a long, long time before the PicoPSU pays itself back though. Since you already have a PSU, I'd recommend using it. Presumably the 380W unit is an Antec-EA380D?
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Old 08-02-2012, 07:47 AM   #3
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In your range, you are probably talking saving single digits of watts by switching PSUs. It will never be worth it...
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Old 08-02-2012, 05:32 PM   #4
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It depends on how you plan to have your server operating.
Personally, I'm making a home server, but I am going to set it to hopefully play nicely with sleep mode, and use Wake on LAN to boot it from sleep, which means while I could save a few watts from a PicoPSU, it won't be that much as hopefully most time should be spent sleeping.

From experience of my own HTPC, where I switched a stock 250w PSU which came with my case (no efficiency certification) for a 150w PicoPSU, it did drop power consumption a reasonable amount, but the cost (a lot) isn't really worth it unless you absolutely REQUIRE super low power for some reason.

Bear in mind also that a PicoPSU will limit your harddrive capacity, if you want internal drives.
My PicoPSU system refuses to boot with 4 HDDs attached. 3 HDD and 1 optical drive is fine, but when I attach 4 HDDs (all 3.5") it refuses to start, which I can only assume is due to the power supply.
My server will use an old Corsair CX400, and the motherboard has 8 SATA ports, so the overhead of the 400w PSU will be offset by the ability to run 7 HDDs + optical drive.

Basically it probably won't be worth it to go for a PicoPSU, especially if you want to fill your system with harddrives.
A low power PSU with high efficiency will be better than a high power PSU with high efficiency, because of what lehtv noted, but 380w is pretty low anyway compared to a low.
While you could get a 250~300w high efficiency PSU, the cost wouldn't be worth it for power savings, especially vs something like just using sleep mode aggressively if it's reasonable to do so.
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Old 08-02-2012, 10:49 PM   #5
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Even in the article you linked, it shows the differences between an already efficient PSU and the Pico as the author decided to update his build:

Quote:
(Update: I ended up replacing my old Seasonic ECO 300 SFX power supply with a Pico PSU-90 plus 60 watt adapter kit. That got the idle power down from 22 watts to 17 watts, a solid savings of 22%. Recommended!)
Depending on what your 380W PSU is (if it's some generic PSU from 1997, you may want to replace it simply because of its age and being a fire hazard). If it's an 80+ certified, don't bother replacing it. If not, I would.

But to break it down use this calculator (just focus on Watts idle and load, your power costs per kWh, and your estimated use). You'll quickly see that it'll probably take around a decade to recoup the initial cost of a new PSU that's more power efficient for those extra 5-10 watts.
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Old 08-07-2012, 03:26 AM   #6
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the PSU I'll recycle definitely isn't from 1997 since it has sata power leads.

And indeed, I plan to fill the case with hard drives. So I will actually need a bit of power.

Thanks for the input!
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Old 08-07-2012, 04:31 PM   #7
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Quote:
Originally Posted by boran View Post
the PSU I'll recycle definitely isn't from 1997 since it has sata power leads.

And indeed, I plan to fill the case with hard drives. So I will actually need a bit of power.

Thanks for the input!
For further reference, my bits arrived today and I've mostly put them together now.

Celeron G530, underclocked to 1.8GHz and undervolted by -0.1v.
B75 mATX motherboard (http://www.asrock.com/mb/Intel/B75%2...Specifications)
2.5" 250GB HDD, set to aggressively power down after 1 minute (just for testing purposes for now)
Total power use 22.5w (flicks between 22 and 23).
Single fan on CPU (92mm I think).

When the CPU was at the stock 2.4GHz with no settings changed, it was ~27w.
This is on a 400w Corsair CX400.

When I add two 3.5" HDDs (3TB each), the power use goes up to 40~44w "idle" (sitting on desktop doing not much).
When aggressive HDD idle settings kick it, it drops down to 28w.
You can see that while idle, the additional HDDs use almost nothing, but when doing something, there's quite a bit more power used, and that's ignoring the MASSIVE power use during spinup, which is where it's really key to have sufficient power.

You can also see that a lot of power savings can come from aggressive settings on your computer, such as low voltages, lower clocks, and HDDs spinning down.
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Old 11-10-2012, 02:45 AM   #8
andru
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wow 27 watts with a 400W PSU. That is VERY efficient. I do not think you would et less with picopsu. What model of PSU was that again, corsair cx 400 V1?
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