[mythtv-users] Power bill vs SchedulesDirect bill

David Rees drees76 at gmail.com
Tue Sep 18 22:55:20 UTC 2007

On 9/18/07, Bearcat M. Sandor <HomeTheater at feline-soul.com> wrote:
> So forgive this ignorant question, but if i have a 500 watt power supply
> does that mean that i'm using 500 watts all the time or that i have 500
> watts of power available?  If i use a 300 watt power supply am i consuming
> less power then i would if i had a 500 watt power supply?

The PSU will only draw as much power from the wall as your components
draw, multiplied by however inefficient the PSU is. So whether or not
the 300w or 500w PSU draws less from the wall with the same load
depends on how efficient that PSU is at the load you have.

For example, if your computer draws 100w and your PSU is 70%
efficient, it will draw ~140w from the wall. That extra 40w will be
dissipated as heat in the PSU.

PSUs will have a sweet spot where they are the most efficient. This
generally runs between 30%-80% of it's peak rated load. Since the vast
majority of computers never even get close to 300w of draw, you
generally will want to find the most efficient PSU with the lowest
peak power capability. These days, this is in the 300-350w range.

The best PSUs will peak over 85% efficiency while being 80%+ efficient
between 20% and 100% load. A PSU which is 80%+ efficient can qualify
for an 80 PLUS certification. See 80plus.org.

silentpcreview.com has great reviews of PSUs including detailed
efficiency reports.


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