kony wrote:

> 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...
>


Oh, so an AC/DC Converter. Right.
Thanks for the info. I"ll look it up and dust off my old undergrad
electricity/electronics textbooks.

> 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.