[TriLUG] OT: Power supply/video card question

[Rob Lockhart]

On Tue, Jul 8, 2008 at 1:15 PM, Joseph Mack NA3T <jmack at wm7d.net> wrote:

> On Tue, 8 Jul 2008, Owen wrote:
>
> > You're right, I should make sure I meet the requirements - I have no
> > recourse if I don't. Thanks for setting my head straight. :-)
>
> The NVidia 8800 needs 500W. I've wondered if these
> requirements are real too. So I went to the NVidia forums,
> where there are stories by people whose machines would (I
> think) occasionally freeze till they upgraded their power
> supplies.
>
> So I would guess the specs are real. The 500W PS from Intrex
> is only $100.
>

A better spec for the video card requirements would be in amperage and
voltage.  One 500W supply from different vendors don't always have the same
current output at one voltage rail (most commonly 12V these days).  They
almost always over-rate the power supplies to make their effective wattage
seem higher than is often achievable, because they only regulate the voltage
on some of the rails.  I.e., 12V drops due to load, if 5V is using the same
transformer, if 12V raises to compensate for power draw, the 5V will then
increase.  Because of I^2*R drops, most newer power supplies should weigh
more heavily towards the 12V rail, whereas older supplies weighted towards
the 3.3V supply.

I would look and see if the card has a PCI-x power supply connector (12V
power supply).    It's a 2x3 connector (3 yellow, 3 black wires). Some
better power supplies have a separate power rail for just the PCIe cards.
Others have more than one, and a dedicated CPU power connector.  If that is
true, it might have a requirement for dedicated current for the 12V rail.
If not, you'll have to see if it's a qualified power supply (if required).