[plug] Anybody know how this thing works?

[Brad Campbell]

Daniel J. Axtens wrote:
> On 8/29/06, Michael Holland <myk at myk.id.au> wrote:
>> On Tue, 29 Aug 2006, Russell wrote:
>>
>> > They have one advantage over PCs: the specs for the one above say that
>> > its power supply brick produces 12 Volts at 3 Amps, which is
>> > substantially less power than an equivalent PC draws.
> 
> 12V @ 3A : P = EI = 12V * 3A = 36 Watts
> 
> Note, however, that 36W is the power the brick puts *out* - if it's is
> 50% efficient (eg old transformer style), the supply draws 72W, but if
> it's 90% efficient (eg modern switchmode) that's ~40W in.

I had a whole rant here regarding the terminology used, but decided just to let it slide (must be 
getting old). Suffice to say that a power supply does not "put out" 36W, but is capable of supplying 
that amount of power to the load while remaining within it's specs. What the load actually draws is 
an entirely different matter. I'd be very worried about a box that actually consumed 36W running 
from a PSU rated at 36W. Does not sound like great engineering practice to me.

<snipped rant regarding terminology, linear vs switchmode, and sliding efficiency scales related to 
load>

>> Draws around 25W idle, 50W max, incl internal 3.5" IDE drive.
>> Dead quiet with a new fan and HDD. Perfect for many Linux appliances.
> 
> That's power in, not power out - the opposite of the supply above. The
> devil is in the detail, as usual :)

Absolutely..

Brad..
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