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PCI express power adapter

 
 
Travis
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      07-18-2010
I have a gts 250 graphics card and it has an 8 pin power slot on the
card, and it comes with an adapter for 8 pin to 2 6-pin plugs. well my
power supply only has 1 6-pin cord, am i supposed to have two? or do
you only need 1.
 
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Paul
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      07-18-2010
Travis wrote:
> I have a gts 250 graphics card and it has an 8 pin power slot on the
> card, and it comes with an adapter for 8 pin to 2 6-pin plugs. well my
> power supply only has 1 6-pin cord, am i supposed to have two? or do
> you only need 1.


Are you sure you're quoting the right part number for the video card ?

Can you provide a URL, leading to a description of the card ?

I want to make sure we're talking about the same card. The examples I looked
at, seemed to be using a 2x3. And the Xbitlabs article on that card,
mentions the power demand is low enough, that a 2x3 is sufficient.

This article has the connector pinouts. It says the "8 pin PCI Express power cable"
has three 12V wires, and five ground wires. I thought one of the tricks was,
one of the ground wires is used for sensing on the video card, to check
whether an 8 pin is connected or not. The 8 pin can carry up to 150W,
and according to this article, the three 12V wires carry a little over
4 amps each. (12V * (3*4.167A)) = 150W.

http://www.playtool.com/pages/psucon...onnectors.html

This adapter might solve the problem, but at this price, I'd expect
the shipping to be free. Note - this solution is only legal in
limited circumstances, such as the GTS 250. You cannot
go crazy, putting these in to solve all problems. This is
converting from a 75W connector to a 150W connector, and you
can't "make watts out of thin air". Such a conversion is only
legal, where the eight pin connector on the video card is a mistake,
and they really only should have used a six pin 75W one. You need
to use an Xbitlabs power measurement, to verify the details. The
GTS 250 is 80W total, a bit over 20W via the slot, leaving less
than 60W to flow through an auxiliary power connector. In such a
case, the adapter won't violate any ampacity rules.

http://www.newegg.com/Product/Produc...82E16812200420

(Product description)
http://www.startech.com/item/PCIEX68...ter-Cable.aspx

*******

Hmmm. Now this is interesting. On page 7 of this
"Electromechanical_Updates.pdf" document, it shows they're using
*two* pins for sensing. And it appears to be OK, as a result of
doing so, to plug a 2x3 into a 2x4 on the video card. It is up
to the video card to enforce the accepted sense codes.
So maybe you don't need any adapter at all. To be safe,
I'd still want to verify the actual power demand, to know
what to expect.

http://www.pcisig.com/developers/mai...11c665ac770768

Connector Sense1 Sense0
------ ------
12V GND
12V GND (Sense0) Ground Ground 2x4 inserted, 150W capable
12V GND Ground Open Reserved
(Sense1) GND GND Open Ground 2x3 inserted, 75W capable
Open Open Dumb customer has not inserted anything

Via the two declared sense pins, the video card designer can
enforce any rules they see fit. They can prevent the video card from
starting, if no Aux connector is present. If they want, they can enforce
that only a 2x4 is used, or they can enforce that either a 2x3 or a 2x4
is acceptable.

If you wish, you can just give it a try with no adapter (plug the 2x3
PSU into the 2x4 video card). If you really have a GTS 250, the power
measurements are here, and a 2x3 is enough. The reason for the double
checking, is to make sure in advance, that no rules are being broken.

http://www.xbitlabs.com/articles/vid...s_6.html#sect0

The breakdown on power is here. 27.93+28.728= 57W, which is less than the
75W limit on a 2x3.

http://www.xbitlabs.com/images/video...power_full.png

If you really have a GTS 250, try plugging the 2x3 directly into the 2x4,
ensuring that the connector is going into the correct set of six holes.
The latches should still line up. Use the playtool.com article, with
all those pictures, as a source of inspiration.

Paul
 
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