[mythtv-users] Help with new Video Card (power supply requirements)

[Christopher Kerr]

On Wed, Mar 24, 2010 at 10:59 PM, Corne Beerse <cbeerse at gmail.com> wrote:
> Then for the real electricians, while dealing with ac, there is also the
> 'cosinus phi' factor:  If you start calculating on stuff like ups-es and
> such, then there is a difference between 'volt-ampere' and 'watt'. I've read
> an article on this at te APC website: www.apc.com.

As an electrical engineering student, I suspect "consinus phi" may be
a medical condition ;o) We call "cosine(phi)", where phi is the phase
difference between voltage and current, "power factor". PC power
supplies have a power factor slightly below 1 - while the load is
inductive, nearly all PC power supplies use some form of power factor
correction. Point is, the real difference between real power (watts)
and apparent power (VA) is small (typically < 10%, always < 20%) for
PC PSU's.

> For your calculation you only need to have a look at the provided power by
> the power supply and the total consumed power of the connected parts. Donnot
> use a way-to-large power supply as they operate best between (roughly) 50
> and 90 % of their max values.

If you buy a quality power supply, you'll note that it has 80+
Certification - this means that it's better than 80% efficient at 20,
50 and 100% load, and has a power factor better than 0.9 (where 1.0 is
ideal). There are also 3 tiers of 80+ certification - Bronze, silver
and gold. Bronze certified products meet the requirements, while
silver and gold products significantly exceed them.

- Chris