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

Corne Beerse cbeerse at gmail.com
Thu Mar 25 12:04:09 UTC 2010

```On 24-3-2010 13:42, Christopher Kerr wrote:
> 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
>
You are right, I failed on my electrical engineering study, but this
most likely is a translation error (I'm Dutch).

> 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.
>
>
True.
```

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