[mythtv-users] external power supply rant (Was: Zotac ION M/B..)

[Brian Wood]

On Wednesday 13 May 2009 12:32:58 Raymond Wagner wrote:
> Simon Hobson wrote:
> > From the efficiency point of view, it means that ALL power consumption
> > goes through two conversions instead of one. OK, there is still the
> > step down for the CPU supply, but 5V and 12V loads will come directly
> > from the PSU and have just one conversion.
>
> Who cares?  DC-DC conversion is very efficient.  Beyond that, the vast
> majority of these machines are going to be dedicated frontend machines,
> meaning they will boot off the network, off a memory card, or at least
> have a hard drive that is kept spun down nearly all the time.  The only
> power draw of concern will be the northbridge, CPU, RAM, and any
> additional chips on the board, all of which will have to go through
> additional voltage conversion/regulation.
>
> The real problem of concern is that 'wall-warts' are cheaply built,
> typically linear, and always low efficiency.  They will be dumping
> easily twice the waste heat of a traditional computer power supply.

I've noticed a trend towards switching circuitry in the wall-warts lately, but 
they are still problematical. Note the problems the early HDHRs had with 
them, as well as the 1212s.

But they do tend to be very inefficient, the vendor is trying to get the cost 
down, and doesn't care about the overall efficiency. With the possible 
exception of folks on this list, have you ever heard of someone not buying a 
product because the included wall wart was inefficient?

Other than space and cooling, a big reason manufacturers use external supplies 
is that the main unit then does not have to be UL certified, only the 
external wart needs to be, and certification is an expensive and 
time-consuming process.

Anything connected directly to the AC mains needs UL certification (in the 
US), but if it has only a low-voltage input(s), those costs are saved. The 
wart-maker is presumably selling enough units to be able to absorb the 
certification costs.

I propose a "wall wart tax", to be assessed against any prodct using such a 
device. We should be able to pay off the national debt in a few weeks.

-- 
beww
beww at beww.org