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"Tune" PSU to increase low load efficiency?

post #1 of 11
Thread Starter 
Hey guys, please share your thoughts if you think this is doable (and if you know how).

If I look on the egg or any other retailer I can't find PSUs to provide lower than Antec's 380W EarthWatts - and 380W is a lot. I need a lower power PSU, so that a low power build @idle would land above the 20% low efficiency threshold - so 150W would suffice. And none of that PicoITX stuff as you can't fit that easily in an ATX case.

...I've been thinking, is it possible to modd a PSU to increase its low load efficiency? Maybe some of the passive components on the PSU PCB would have to be "tuned" for lower load... what do you guys think?

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post #2 of 11
http://www.newegg.com/Product/Produc...82E16817151086 - Seasonic 80 bronze, 300W, still too much but much closer, I'm sure @ 50% load you would be getting into the 80% area
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post #3 of 11
Thread Starter 
Quote:
Originally Posted by appleg33k85 View Post
http://www.newegg.com/Product/Produc...82E16817151086 - Seasonic 80 bronze, 300W, still too much but much closer, I'm sure @ 50% load you would be getting into the 80% area
The problem is there's no way I can reach 50% load, most of the time it'd be around 10%. Still, thanks for the suggestion.
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post #4 of 11
Query: What is your reasoning behind this?

The EA380 costs about $35 roughly, so I don't think you're going to find a modern PSU for a much cheaper price, regardless of wattage. If you're in some sort of super energy efficiency mindset, let me just say that's rather crazy. i.e.

"At 90W load,

* the 300W model would generate 23W of heat (20.5% of 113W AC input).
* the 600W model would generate 32W of heat (26% of 122W AC input)."


The difference between a 300W and a 600W PSU at low loads is 9Watts (which is basically nothing, and that was a crappy Enermax 600W PSU not a modern day efficient 80Plus PSU). The difference between anything smaller than a 300W and a 300W will really be nothing. So unless there is some really unexpected reason, or this is a hobbyist thing I'd say just bite the bullet on a 300W PSU.
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post #5 of 11
Thread Starter 
Quote:
Originally Posted by ocpokey View Post
Query: What is your reasoning behind this?

...

The difference between a 300W and a 600W PSU at low loads is 9Watts (which is basically nothing, and that was a crappy Enermax 600W PSU not a modern day efficient 80Plus PSU). The difference between anything smaller than a 300W and a 300W will really be nothing. So unless there is some really unexpected reason, or this is a hobbyist thing I'd say just bite the bullet on a 300W PSU.

This is a pic taken from TR's review of the Brazos platform that can be found here.

It clearly shows the same rigs (Atom & Brazos) that consume
*on a regular ATX PSU: 50W @load & 45W @idle
*on brick+dc/dc converter 25-27W load & 14-21W idle

Worse case scenario: Brazos @idle when powered from an ATX PSU: out of the 45W, at least 31W (69%) are losses, not including the watts lost in the brick+dc/dc. 69% losses!

Answer to query: if the idle load is low enough, say below 60W (which is reasonable looking at the graph above), then any ATX PSU available runs below 20% of its rated power with very bad efficiency. I would like to tweak a regular ATX PSU to increase low load efficiency even if this means decreasing its maximum rated power because I find more useful to have low losses than high W numbers.

______
P.S. My guess is 90% of the rigs being build by OEMs or in retail with 2011 components rely in IGP, thus have low idle power. Since those that make 80+ standards ignore the <20% load efficiency no one is encouraged to make low power & efficient PSUs, so I'm thinking of making my own with the help of OCN.
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post #6 of 11
I'm not debating that those rigs use little power, I'm debating that there is any point to worrying about it. Even the maximum (not minimum) loss to heat of 31W means that if you ran your rig 100% idle 24/7 for a month, you would save 23.4KWh of energy.
In terms of money that equates to roughly $2.50 .
And if you are super serious about saving energy I'd argue that rather than running a rig at full idle 24/7, you could turn it off as the most efficient choice. And as the article says, if you are running @load, modern day more powerful systems are actually more efficient (since they complete tasks much faster).

I don't mean to shoot down your idea, it certainly might be a fun project, but let's keep it real, and not say stuff like "oh no you are taking huge energy losses with larger PSUs", because we're actually really dealing with tiny numbers here.
Edited by ocpokey - 2/22/11 at 6:16am
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post #7 of 11
Thread Starter 
Your calculation is correct, and it's true that not the money are the limiting factor. However there are other things limiting the max power such as the available thermal budget that can be evacuated from the enclosure and airflow (noise) necessary to do so.

The thing is Intel, AMD, Nvidia, ARM, Apple, SSD/HDD manufacturers provide devices with higher efficiency to such extent that nowadays an Core i5 750 with a 6970 can idle below 60W. And they are idle most of the time while browsing, working, etc. PSU manufacturers don't seem to follow by offering something to address this trend. They could pack a laptop brick & a PicoITX PSU in an ATX PSU enclosure, but they don't.

I don't agree with:
Quote:
"oh no you are taking huge energy losses with larger PSUs", because we're actually really dealing with tiny numbers here
31W makes for 36$ per year where I live. One could buy a 500GB HDD for this money or maybe a haircut (which many desperately need and this kind of development would enable them to look decent at least once a year ).
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post #8 of 11
It's a great idea, but not really practicable. Most of the losses at that low load are due to the fact that the entire power circuit needs to be energized with a minimum amount of energy in order for the PSU to stay on. Plus power required by the +5VSB circuit and the controller circuitry. These are attributes of the design and can not be changed.

It may be possible to design a power supply to operate with high efficiency at low load, but it is not possible to modify an existing one in such a way.
post #9 of 11
Thread Starter 
Quote:
Originally Posted by Phaedrus2129 View Post
It's a great idea, but not really practicable. Most of the losses at that low load are due to the fact that the entire power circuit needs to be energized with a minimum amount of energy in order for the PSU to stay on. Plus power required by the +5VSB circuit and the controller circuitry. These are attributes of the design and can not be changed.

It may be possible to design a power supply to operate with high efficiency at low load, but it is not possible to modify an existing one in such a way.
bummer Thanks for the reply though.

Transformer's magnetizing current can't really be changed, but I was hoping that's a small(ish) part of the losses. Also the reverse current of the diodes/transistors can't be changed unless I change the PCB altogether. Since I'm not much a of a µelectronic specialist I was hoping I was missing something and could be done.

...the good part of this thread is that I found a side-solution. I'm gonna try to tweak a laptop brick and a pico-ITX PSU in an ATX enclosure. I'm off shopping
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post #10 of 11
The more I read about PSUs, the more I want to know. I thought this thread was very interesting.

On a side thought, one way to get around the problem, is throw in a Fermi to fold 24/7
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