Firstly, let me say that the reason I would want a PSU *with* a 12cm
fan is because, as you say, it is more quiet and efficient - as long as
that is true.
But looking at the close position of items in the case and the location
of the 12cm fan at the bottom of the PSU, I am concerned that it might
"compete" with the case exhaust fan which is at a right angle to the
bottom of the PSU. I'm also concerned that the CPU HSF will at least
partially obstruct airflow to the bottom of the PSU.
If OTOH, there was sufficient space and a sufficient gap between these
items and the PSU, then the 12cm fan starts to look like a great idea.
I would definitely feel comfortable about using a PSU with 12cm fan in
a case like this one where there would be a fairly large gap between
the bottom of the PSU and the other items:
You guys are going at this the wrong way.
An ordinary cheap power supply, might have an efficiency of 68%.
A modern, efficient power supply improves the efficiency of
the conversion to 80% or slightly more. 80%+ designs are in
the minority, and the asking price is usually higher. If you
live in a country with a high electricity cost, the payback
period on the 80% unit is a lot shorter.
Now, lets make 100 watts DC output with each unit.
The first unit draws from the wall 100W/0.68 = 147W. That is
47W of heat, and 100W of useful power for the motherboard. The
47W of waste heat in the conversion, has to be removed by the
PSU fan.
Checking my calc - 100W output
----------- = 68% efficiency
147W input
The second unit draws from the wall 100W/0.80 = 125W. That is
25W of heat.
How does that difference affect the power supply design ?
1) I can use a shorter heatsink and keep my regular air volume
in CFM (cubic feet per minute).
2) I can use the same sized heatsink, and use a much slower fan.
(Well, the fan cannot get much slower and still be spinning.)
3) I can do a little of both, making the power supply a bit
lighter in terms of the weight, and making more room for
whatever fan solution the marketing department likes today.
The choices start with the core of the design. The fan size and
spacing, are determined by the choice made for the core of the
design. An 80%+ efficient design has a lot more room to move
stuff around inside the packaging, while a 68% design is
hard pressed to get enough heat sinks in there.
Seasonic calls their conversion method "forward conversion",
but in a quick check in Wikipedia and related links, forward
conversion looks very much like the method they all use.
I must be missing something, if "forward converters" are
something special. Still waiting to see an article that
explains how the Seasonic method works. I'm sure the other
fly-by-night companies would have copied this method by
now, unless it is covered by patents or licensing issues.
Maybe the parts cost is higher.
"HISTORY OF THE FORWARD CONVERTER", hints at the wide
variety of approaches that have been tried:
http://encon.fke.utm.my/nikd/latest/JulyHistory.pdf
"The two-transistor forward converter is a modern-day
standard for off-line power from 200 W to 1 kW. Many
companies use it as the basis of their product lines."
Paul
