On Wed, 17 Aug 2005 05:46:43 -0500, Analabha Roy
<daneelNOSPAM@physics.utexas.edu> wrote:

>kony wrote:
>
>> On Tue, 16 Aug 2005 08:52:47 -0500, Analabha Roy
>> <daneelNOSPAM@physics.utexas.edu> wrote:
>>
>>>
>>> Can anybody say anything about that with these specs?
>>>
>>>http://www.coolmaxusa.com/productDet...ategory=single
>>>
>>>
>>
>> That they're peak ratings, not sustainable. Essentially
>> they use questinable methods to determine those numbers and
>> if other name-brand manufacturers used similar methods,
>> their "400W" psu would be rated higher than 400W.
>
>
> That's a good point I guess...
>
> But what is a psu exactly? Isn't it just a step-down transformer with some
>pots in it to regulate voltage?

Not exactly it swithces HV across a transformer at high
frequency with a duration or rate controlled by (a
controller, to regulate the voltage through at least one or
multiple feedbacks) into rectification diodes and (typically
inductive and capacitive) filters...

That's an oversimplification and ignores complimentary
circuits like the shutdown, fan control, 5VSB, and more,
but thinking "it's simple therefore should be cheap" isn't
true, as any kind of electronic components have tolerances,
values, and more or less elaborate designs including the
filtering and lifespan. There are a few PSU schematics
scattered over the web, Google may find some. Unfortunately
those I've seen are rather simple schematics, more typical
of low end PSU that decent ones.

I'd return the PSU you bought, but you might pop open some
old generic and compare it to a decent PSU. WIthout more
experneice in switching PSU you may not realize the
significance of all of the differences but even an untrained
eye can spot a lot of difference between two "supposedly"
400W PSU, one good and one not.

>I mean, it doesn't actually supply any
>power, right? That comes from the mains.

You might be trying to overthink the definition of supply,
and should see it within the context of an electronic
device... within that context, it is suitably called a
"power supply".


>The 'sustainability' would have to
>be more dependent on material properties (if the impedance changes too much
>as it gets hotter and if subsequent cooling reverses the trend)like
>resilience and stuff. If that is true, then the only manufacturing
>difference between a high power and low power psu is in the materials that
>make the magnetic core, maybe the CPM of the fan, the # of coils in the
>transformer and other similar such. Those should be individually measurable
>and benchmarkable, and there should be documentation on the web about ideal
>parameters and one should be able to compare them.

Yes the parameters can be physically compared, though again
you're oversimplifing. You have a good point about the core
though, the size of the transfomer is indeed "one" of the
common differences between a properly rated and a misrated
PSU, and/or the construction of the core, whether it be a
ferric composite material or old school laminate type. If
you dig deep enough you will find that budget grade (junk)
PSU cut corners in many, many ways. You will notice more
similar build in a generic 400W and a name-brand 250W than a
generic 400W and a name-brand 350W.



>
> Let me know what you think. Also, if you do know of some urls where they
>have additional info, I'd be interested in reading it.


I would first suggest some background reading, either on
switching power supplies in general or if necessary, even
more basic like electronics in general. It's not the kind
of think I can condense into a few usenet posts and I don't
know of any website that does so either, as you first need
the requisite background on power, electronics, SMPS,
computer power demands, then to tie it all together in
context plus survey enough power supplies (including failure
modes of dead ones) to get a better picture.