[mythtv-users] Help with new Video Card (power supply requirements)
Corne Beerse
cbeerse at gmail.com
Wed Mar 24 11:59:29 UTC 2010
On 12-3-2010 21:19, Paulin wrote:
> All,
>
> I just purchased a new video card (Jaton 498pci -
> http://www.newegg.com/Product/Product.aspx?Item=N82E16814139046).
> Anyway I was getting ready to install it and one of the requirements
> on the box says minimum 450W power supply. Anyway I checked my dell
> box and it told me the V 115 with 7 amp. So simple math sells me 700+
> watts. Then I opened up the box and on the power supply there is a
> label. It says that max power is 300 watts.
>
> So my question is my thinking correct, in that, I can't use this card
> because my power supply is maxed at 300w.
>
> Since V x A = W why does the power supply say 300 max?
>
> So should I return the card and look for something else or will this work?
>
For a starter you made some reasonal assumptions. However...
Your dell box was labeled 115V and 7A separately, which indicates that
it operates nice at 115 Volts (give or take 10 %) and that the max
current it will require is about 7 Amps, hence the fuse must be at least
7 Amps, otherwise it might blow in normal operations.
For a powerbox, with volts and amps both at the imput and the output,
you have to note the efficiency of the powerbox. If it produces 12 volts
with 2 amps and 5 volts at 5 amps, it outputs 24 and 25 watts. With
that, it will consume more than 49 watts at the input, the remaining
power is converted to heat and maybe some light (a power-led or such)
and other radiations (distorsion on radios) too.
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.
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.
CBee
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