[mythtv-users] The elusive silent myth BE/FE box [in search of]

Raymond Wagner raymond at wagnerrp.com
Sat Aug 20 23:37:12 UTC 2011

On 8/20/2011 18:30, Epinephrine Junky wrote:
>> (iii) Your pico-PSU may sound a good idea but remember you'll get losses
> in the power brick as well, say 7 to 10W.
> True but the beauty of that is that the heat is dumped outside the box so
> it doesn't contribute to (over)heating the CPU.

Not exactly.  Say you've got a system that tops out at 100W.  That power 
supply is going to add another 15-20W into the mix.  However that power 
supply is dumping straight out the back of the system, and drawing air 
from inside the system to do so.  Not only is it not making the system 
hotter, it's actually helping to cool it.

Things like the PicoPSU are fantastic if you have an existing 12V power 
distribution system, or want to hook it up in-line with a battery 
backup.  If you are just going to plug it into a power adapter, the only 
thing it gets you is a smaller lighter case, in exchange for a big brick 

>> >  (iv) I'd say you would be mad to try and run this without anything but a
>> case fan.
> Maybe but I've been called worse.  I was thinking of these fanless
> systems:
> http://www.endpcnoise.com/cgi-bin/e/std/sku=hfx_classic_fanless_htpc.html
> If I had the $ to spend they seem to have the right idea... just way too
> expensive.

They don't quite have it figured out.  The lack of fans on that much 
power is severely restricting.  First, you have to rely on convective 
currents for all your cooling, which means you need to be out in the 
open.  If you have anything within half a foot on either side, there is 
not going to be enough airflow over those fins to cool it.  Similarly, 
if anything is placed half a foot or so above it, you're going to block 
those currents, and the system will overheat.  This is something 
designed to sit on top of a table next to your TV and look pretty.  
Putting it in an AV rack is out of the question.

Second, the only things they cool are the CPU and graphics.  There is no 
provision for cooling the memory, power supply, chipset, or MOSFETs.    
They're using a fanless power supply.  Fanless power supplies expect 
that the case will supply sufficient airflow through it to make up for 
its own lack.  Antec designed their dual chamber cases specifically to 
allow for such power supplies, to ensure they had enough airflow through 
them for stable operation.  If you don't cool those and run the system 
hard, they're going to overheat, their rated output will drop, and their 
voltages will go out of spec, leading to system instability.

Memory needs cooling.  Un-cooled memory will heat up, and lead to 
reduced stability.  They did go with one stick of pretty low end stuff, 
which should help in this regard.  Modern motherboards all have big 
heatsinks around their chipsets and MOSFETs, and these are arrayed 
around the processor, with the intent of scavenging airflow from the CPU 
fan.  With no fans, they don't get this, meaning they heat up, and 
again, reduced system stability.  These things seem nice in concept, but 
at least in my opinion, they've overlooked too many issues for me to be 
comfortable using one.

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