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the efficiency

post #1 of 12
Thread Starter 
How exactly does the efficiency rating work?
As a more or less constant factor regardless of load or starting high, decreasing as load increases (or other way around) ?
post #2 of 12
It's just a rating that tells you how efficiently a PSU uses it's power.

If it's pulling 300w from the wall, and is outputting 250w, divide 250 by 300, and you get .83333333, or about 83% efficiency.
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post #3 of 12
Generally low efficiencies at low loads (70% or even lower), then climbing to a peak in the average load range, and then slightly dropping off a little at peak loads.

That's how generally the efficiency of a PSU looks like.

Pull any review up from Jonnyguru.com, and you'll see a pattern like that.

Here is an example:
http://www.jonnyguru.com/review_deta...=32&page_num=2

See the 79% load at 133W load, then 82-83% at medium range loads, and 80% at high load. This PSU holds up VERY well... some show much more dramatic differences (esp. at low loads)
    
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post #4 of 12
Thread Starter 
Ok. But I'm going to use the PSU for powering more than one node in a cluster.
what I'm thinking of doing, is to get a decent high efficiency PSU and split the atx-cable into two or more. I haven't calculated the actual usage of each node, but it isn't much.
I've read that the thing to go for actually is a powerful single-rail, but any recommendations on this plan?
I'm going about it this way because I can't find any low wattage PSU's that fits my wish for high(est) efficiency and preferably RoHS.
post #5 of 12
Try to get into touch with Cyberdruid. He did run two rigs (mobo, CPU, onboard graphics, hdd) of a single PSU. He used the 560W Silverstone Zeus for it, which has a single 38A 12V rail.

However, there are currently more powerful PSUs with a single rail, such as the PC P&C Silencer series, and the Silverstone OP and DA (Olympia and Decathlon) series.

For your specific purpose, the DA series might not be a bad idea... modularity is probably quite a benefit for you.
    
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post #6 of 12
Thread Starter 
Sorry for late reply. for some reason I don't get notifications though subscribed.
I've asked over at frozencpu whether I can purchase single atx-cables for the modular PSU's in their product line, and described why, but they haven't replied
The thing I worry about the most, with just splitting up the atx cable into 2+ is that if e.g the 3.3V can draw say 5 amps at most, I probably won't be able to get in to the most efficient range of the PSU before hitting the ceiling on amperage.
A loose, but not too far off guess, is a use be each node at around:
CPU @ 35W
RAM @ 2.88W, 1.6A.? datasheet(pdf)I'm not too sure on how to understand the specs for a total usage from the set.
And something for the MB which probably isn't that much.
So probably around 50-100W pr. node (except a 'main' node with DVD-burner and harddrives.)
But I might be worrying for no reason.
post #7 of 12
35W is a very low estimate for a CPU... not sure which CPU you're looking at. Plus, if you overclock, it will increase quite a bit.

RAM draws from the 3.3V rail, as do some other motherboard devices. If we look at this PSU:
http://www.newegg.com/Product/Produc...82E16817256017

We see that it delivers 28A on the 3.3V rail, 30A on the 5V rail and 60A on the 12V rail. I don't know how many nodes you're planning? I'd say this one can handle four quite easily.
    
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post #8 of 12
Quote:
Originally Posted by Chozart View Post
35W is a very low estimate for a CPU... not sure which CPU you're looking at. Plus, if you overclock, it will increase quite a bit.

RAM draws from the 3.3V rail, as do some other motherboard devices. If we look at this PSU:
http://www.newegg.com/Product/Produc...82E16817256017

We see that it delivers 28A on the 3.3V rail, 30A on the 5V rail and 60A on the 12V rail. I don't know how many nodes you're planning? I'd say this one can handle four quite easily.
Hey Chozart, I thought that RAM pulled from the 3.3v rail as well. However, I saw a recent chart in MaximumPC saying that DDR2 pulled from the 5v rail. Any ideas?
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post #9 of 12
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post #10 of 12
Thread Starter 
Quote:
Originally Posted by Chozart View Post
35W is a very low estimate for a CPU... not sure which CPU you're looking at. Plus, if you overclock, it will increase quite a bit.
I'm currently planning on using AMD Athlon 64 X2 3800+ 2 GHz (ADD3800CUBOX), chosen specifically for the low TDP, which AMD support told me can be used as a measure of the power draw. And it's cheaper than a similar core2duo<=35W TDP.
And you're right, over clocking will be used, so the total draw will be higher than the producer specs.
I was browsing PSU's again and I think Silverstone Olympia OP750 750W might be a decent choice for a first PSU. Little cheaper than the DA750 too, and RoHS .. which DA750 might be too, but it isn't stated. And it carries the same specs of 28/30/60A.
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