"kony" <spam@spam.com> wrote in message
news:ol21i3l5uljd1mjaeek8ouno42vg7v1obb@4ax.com...
> On Thu, 25 Oct 2007 03:07:13 -0700, "JB"
> <highlinex@yahoo.com> wrote:
>
>>It seems like both industries operate in a vacuum.
>>
>>I looked at a video card whose requirement was "a 350 W PS with 22 A
>>available on the +12V rail".
>
> ... but you didn't mention the card nor the rest of the
> system. Since a video card manufacturer can't know other
> system details, they just have to generalize because some
> psu aren't honestly rated and they can't know the 12V
> current the rest of the system uses.
>
>>
>>Most PS ratings that I checked are rated for a maximum of around 18A on
>>the
>>+12V rail regardless of the advertised power rating.
>
> You haven't checked many online then? Newer generations of
> higher wattage PSU typically have more than 18A rating,
> though sometimes it is for current on multiple 12V rails
> which is ok, since one rail on modern systems powers the CPU
> which is part of the consumption the video card manufacturer
> factors in when spec'ing 22A.
>
>
>
>>
>>Some have dual or triple +12V rails whose combined ratings may be 36A or
>>higher.
>>
>>So how do we make a determination as to what the video card really needs
>>and
>>how to provide it?
>
> Start with details. Video card, CPU, # of hard drives, PSU
> make/model/rating.
>
>
>>
>>Some would, I suppose, put the rails in parallel and hope for the best.
>>But
>>if the PS is not designed for that mode, the result could be instability
>>with unpredictable effects.
>
> Not necessarily, depends on the specfics. Generally if the
> rails are truely in parallel it is more versatile, not less.
>
>
>>
>>If the actual load requirement for the video card were disclosed, we could
>>make some guestimates as to all other loads and choose a power supply that
>>would probably work. IMO the video card requirement is ridiculous and
>>shows
>>a lack of concern for the customer.
>
>
> I agree the video card manufacturers should plainly state
> current:rail consumption, it would make things a lot easier
> for those who know the other variables in their system. It
> is a shame the engineers and marketing departments can't
> (dont') provide these specs. You can have some idea of
> certain models of psu that are shown acceptible with your
> card by seeking fellow users of same card with equivalent
> systems, but cold hard numbers are always the more accurate
> way to go.
>
>
> On the other hand, it is seldom a good idea to buy a PSU
> with barely enough capacity rather than one with quite a bit
> of margin, not just for stability reasons but to achieve
> longer life. Granted, sometimes even that is not enough,
> certain PSU cost corners like poor fans or capacitors might
> reduce life regardless of having a capacity margin, but
> generally if one has the budget for a power hungry video
> card it just makes sense to put a bit more of the budget
> into a higher quality and capacity PSU as well.
>
> There are some online comparisons of video card power
> consumption, if you're lucky a Google search might find one
> that has tested your card or at least same GPU, memory,
> frequencies... even if a different brand of card it should
> be very close to same power consumption as they're generally
> built on the same reference design or at least close enough
> to that in consumption even when certain manufacturers like
> MSI or Asus decide to change the design a bit.<

Thank you for your input Kony. I am sure you can do a power budget and
allocate it per rail but that is not what I need.

I am savvy on the engineering considerations but my gripe is with the
ribbon- clerk type disclosure of power requirements.

For example, the particular card whose requirement I mentioned as being 22A
on the 12 V rail is an EVGA 8600GT. My gut feel is that the card does not
need anywhere near that much current. In fact, IFhe link below gives the
power dissipation for that card as being 30W, not the 264W implied by the
requirement on the box. So, IF the numbers at the site are correct, the
card itself needs 2.5 A.

http://www.atomicmpc.com.au/forums.asp?s=2&c=7&t=9354

Obviously EVGVA's intent is to tell the customer his total system needs that
much capability on the 12V rail...a prognistication only a true seer should
make. But that is not what they say so it's worse than no information at
all AFAIC.

BTW, that card is just one example, it's not one I intend to buy. I know
other companies put similar requirements on the customer and think it's just
sloppy work across the board. I don't think a user should have to buy a
clamp-on ammeter and verify the ratings.

When I get my components selected I will select a PS and then see what you
folks think.

Thank you.

Mike