PCI-e PS question.

[Vega]

Will PCI-e SLI setups need special power supplies or just high wattage? What is PCI-e power cables people are talking about. Doesn't like a PCI-e 6800 just have a slot to plug in a molex connector?

 

[v_lestat]

no not a regular molex its a special plug. and the only power supplies out there right now that have pci-ex plugs only have 1 plug.

also make note there is a sticky about sli and power supplies. check it out.

be aware of the power requirements for SLI. your gunna have to have an insanely large power supply costing well over 300 bucks
or
your gunna have to run an additional power supply for the second card.


i dont see why they did that. with the last batches of psu;s coming out lately they have an enormous amount of wattage and amp's.

id contact nvidia or find a good reference for power requirements cuz im sure its huge.

i havent done any kind of research into this , im only repeated what i have read and heard other people say.

 

[Ice Czar]

your gunna have to have an insanely large power supply costing well over 300 bucks

LOL
somehow I doubt that though considering the cost of SLi that wouldnt be unresonable
its not the watts but the amps that will be important (though obviously they are related)

Its likely that with 34 Amps on the +12V rail (nominal, 38 Amps Peak)
a PCP&C Turbo Cool 510 (one of the best Desktop PSU made)
will easily power most SLi configs it runs $200
(Provided you also dont add in an extra CPU, large RAID array ect)
and many other PSUs are now pumping out 30 Amps on the +12V rails

lets say we have two 6800 ultras as the power estimate
so...
+3.3V @ 0.17 Amps x 2 = 0.34 Amps
+5V @ 4.29 Amps x 2 = 5.58 Amps
+12V @ 4.32 Amps x 2 = 8.64 Amps

nowadays most supplys are under utilizing the +3.3V and +5V rails so they arent all that important
but the extra 8 or so amps on the +12V rail could make a supply anemic on that rail

lets take a basic config and add in those figures (well I did give it 2GB of RAM )
http://takaman.jp/D/?M=PbQBQbdXhSASrTITnUCkG5@CDxIWZAZavPCOP&english


so..

+3.3V @ 2.6 Amps
+5V @ 13.5 Amps
+12V @ 22.2 Amps
Total output 353.1 Watts
of course that is actual draw, not the size of the PSU
PSUs are rated at 25C more often than not and that means that at the realworld operating temperature of 40C or so, they are putting out lets say a third less then their rating, and thats if they are well made supplies by a reputible manufacturer, otherwise the fudge alot more than just the temperature (see below)

so Id say any good PSU with greater than 30 Amps on the combined +12V rails
will likely power a basic config
and I can think of at least one that is under $100 that will likely do it

my "formula" for mixing up a batch of kickass PSU

and

POWER SHMOWER by Mike Chin

or How PSU Power Ratings Mean Almost Nothing

A frustrating fact about PSUs is that there does not appear to be a stringent or regulated standard for reporting, advertising and labeling rated power. This is despite the existence of standards like ATX2.03 or Intel ATX12V.

There are well-established standards for measuring and rating HDD capacity, an engine's horsepower, or the heat generated by a furnace... but not one for how much power a PSU can deliver. There are so many cases of people with "450W" PSUs having power stability issues running a system that can't possoibly draw more than 150W. And "300W" units that keep running where the "450W" units are faltering.

It's not just about bad PSUs vs better ones. It's a dumb situation caused by uncontrolled marketing competition. Real regulation would bring PSUs out of snake oil territory and into a more sensible consumer-friendly terrain.

There are many ways PSU makers fudge to make their units seem more powerful.

1) Out and out lying. You add up the power on all the lines in many PSUs and they fall short of the rated power by 10, 20 30W or even more.

There are more sophisticated ways:

2) Limit the AC input voltage to a very narrow tolerance. The best PSUs are able to deliver their rated power given a decent range of AC input power, say 90~130V for a 120V unit. It's much more demanding to produce 300W w/90VAC input than with 120VAC, so what some PSU makers will detail in their tech specs (usually not in their consumer brochures) is to specify 115-120VAC for input power. A PSU specified this way will not deliver full power if the AC voltage sags, if there is a brown-out. Surely it causes instability more often than a PSU rated to deliver full power with 90-130VAC.

3) Specify a low operating temperature for rated output. This is quite common, but again not often seen in consumer brochures, but rather tech spec sheets provided usually only on demand by engineers or corp buyers. A typical PSU operating temp statement is somthing like this:

0ºC ~25ºC for full rating of load, decrease to zero Watts O/P at 70ºC

Examine what that says. Full power (let's say 400W) is available when the unit is at 0ºC ~25ºC. Hmmm. Think about this.

Have you ever felt air blown out of a PSU in a PC running absolutely full tilt (which it would have to do to get anywhere near 400W output) that felt cool to the fingers? 25ºC airflow would feel exactly that: Cool, given that normal body temperature is 37 °C.

So this PSU cannot deliver full rated power when its temperature goes over 25ºC. OK, what happens to the max power output capacity above that temp? It decreases gradually so that by the time the PSU temp reaches 70ºC, the PSU cannot deliver any power at all. So if you assume that this power drop as temp rises is linear, then max power capacity will drop by ~9W for every degree over 25ºC.

Now having examined as many PSUs as I have over the last 2~3 years, I have to say there's not a single PSU in ANY PC I have ever used or examined that would not measure at least 30~35ºC almost anywhere inside the PSU under almost any kind of load. And if/when it is pushed, 45ºC is nothing at all, especially for or near hot running components like voltage regulators.

So let's say 40ºC is a fairly typical temp inside a PSU. This 400W rated unit would actually be able to deliver a max of just 220W at that temp. Hmmm. Interesting, isn't it? At 50ºC, the available power would drop to just 130W. No wonder some PSUs have 3 fans each capable of 50 cfm!!

Here's a simple fact: Really high quality PSUs are actually rated for full power output at as high as 40ºC. The trick is get a hold of the spec sheets that tell such information so you can compare apples to apples. Or ask.

or

from dansdata

Unethical PSU Marketing 101.

Here's how to make overly optimistic power supply specifications. It's really simple.

First, power the thing up. You can make an ATX power supply that isn't connected to a motherboard turn on by grounding pin number 14 on the big motherboard power connector. It's easy to spot that pin, because it's the only one with a green wire going to it.

Use any handy bit of wire - like the paper clip in this picture - to connect pin 14 to any ground contact. The ground contacts are the ones with the black wires going to them. Presto, the PSU will turn on.

Now, break out your brick-sized power resistors and load the heck out of one of the output rails - the +5V rail, for instance. Measure the current as you increase the load, until the voltage sags unacceptably far below the rated voltage.

How do you tell what an unacceptable voltage sag is? Well, you could choose a nice conservative small permitted sag - say, 0.1 volts - so that your results are genuinely useful to your customers. Or you could just ignore the voltage and say that when a fuse (or some other component...) blows, that must have been the limit, right there.

OK. Now you've made a big fat amperage number for the +5V rail. If you blew up the PSU in the process, get another one, and repeat the process for +12V and +3.3V, and for the low current rails as well.

On no account, though, should you test more than one rail at a time. This is the key to the whole scam.

A big beefy PSU may be able to deliver 50 amps (say) on the 5V rail when nothing else is under load, and 25 amps (say) on the 12V rail when it's similarly all alone. But the 12V and 5V rails together may only be able to deliver, say, 350 watts between them, when they're both under load. Watts equals amps times volts.

In a real PC, all of the power rails will always be under load together.

But you're not testing what the PSU can really do - you're making pretty numbers for the sales brochure!

So test all of your rails alone, get an amperage figure for all of them, multiply that figure by the voltage of the rail it came from (the nominal voltage, not whatever the voltage had sagged to as the PSU pumped electrons through the dessert spoon you'd soldered to the circuit board), then take all of the resulting wattage figures and add 'em up. That's a wrap, folks. Ship it!

 

[v_lestat]

like i said
i only know what i read here and other places.

this section has its own thread about a power supply with only 1 pci ex connector.

so your gunna have to have a psu with 2.
each on its own rail i would imagine. but again i could be wrong.

but you never know sli mode could be power hungry beyond belief. i just wish they would hurry up and release the friggin specs and requirements and some reviews.
so we know what hardware is needed.

sli isnt for the poor or average gamer so to assume becuase of the sli pricetag that your gunna get by with 34 amps is foolish especially when other things will be using that same rail.
and are you sure those cards are using the 12v rail ?

just food for thought since i havent looked hard enough yet to see the power requirements for SLI

 

[Vega]

I found out molex to PCI-e adaptors are available, so yes, you could use a regular high wattage PS to run SLI.