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Potential Limitations of PCI-E 6-Pin to 8-Pin adapters

post #1 of 48
Thread Starter 
I'm starting this thread to warn others of the potential risks of using PCI-E 6-Pin to 8-Pin adapters.

PCI-E Connections (Official Wattage)
PCI-E 6-Pin - 75W
PCI-E 8-Pin - 150W

Difference between PCI-E 6-Pin and PCI-E 8-Pin
The only physical difference between PCI-E 6-Pin and PCI-E 8-Pin connections is two "ground" wires which will not increase amperage, however may increase stability. This to me seems purely for marketing. So in theory PCI-E 6-Pin connections should be capable of supplying 150W, with each individual 18 AWG cable rated at 4.15A.

Potential Risks
Because of the above this leads people to use PCI-E 6-Pin to 8-Pin adapters. However without knowing amperage distribution and internal wiring, I would strongly advise against using PCI-E 6-Pin to 8-Pin adapters.

Example
Silverstone 600W SST-ST60F Modular
+12V1 – 13A
+12V2 – 18A
+12V3 – 16A
+12V4 – 8A

Now this powersupply comes with two modular PCI-E cables that split into four PCI-E 6-Pin connections. The first PCI-E cable uses the +12V3 rail, and the second PCI-E cable uses the +12V2 rail. Remember each cable splits into two PCI-E 6-Pin connections, so there will be four in total.

Now the GTX 295 needs both PCI-E 6-Pin and 8-Pin connections, so the user will need a PCI-E 6-Pin to 8-pin adapter, now if they used only the first PCI–E cable for both PCI-E 6-Pin and PCI-E 8-Pin connections. Then the maximum amperage would be 16A. So the maximum possible wattage would be 190W, this falls short of the official 225W for the combined wattage of PCI-E 6-Pin and 8-Pin connections. However the combined load of the powersupply 12V rails is 504W, which is 42A. So you most definitely won’t get 190W from the +12V3 rail. More like 150W which would be unable to power a GTX 295.
Edited by xtremetechuk - 3/16/11 at 10:48am
post #2 of 48
doh.gif

go learn something useful

http://www.jonnyguru.com/forums/showthread.php?t=7212
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post #3 of 48
Thread Starter 
Quote:
Originally Posted by obsidian86;12740958 
doh.gif

go learn something useful

http://www.jonnyguru.com/forums/showthread.php?t=7212

Maybe you should read the thread yourself, the thread states that the PCI-E 6-Pin connections can supply 150W. Which is basically what I stated, except that I have also explained the potential risks of using PCI-E 6-Pin to 8-Pin adapters.
post #4 of 48
Forgive me, but I am not understanding the point of this?
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post #5 of 48
It may be a valid point but I think that if a builder looks over their option of components they can avoid issues such as having to adapt.

I bought my Seasonic X750 and X650 Golds and they are the 6+2 pins so I see that has been thought out by this builders design

I find many of the issues are the builders trying to cut a budget or they buy components for looks rather then functionality and performance.

At least this may save a few users in the future so it isn't a bad post by any means.

wink.gif
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post #6 of 48
Quote:
Originally Posted by xtremetechuk;12741141 
Maybe you should read the thread yourself, the thread states that the PCI-E 6-Pin connections can supply 150W. Which is basically what I stated, except that I have also explained the potential risks of using PCI-E 6-Pin to 8-Pin adapters.
Quote:
Here's the actual Molex Mini-fit Jr. datasheet (and another). With 6 active circuits (3 power + 3 ground), the basic mini-fit is rated for 7 A/contact (21A @ 12V = 252W), while the high current (HCS) contacts are rated for 12A (36A @ 12V = 432W).

i dont see the problem even if you got crappy conectors they can handle 250 watts and if you got the good ones you are good for 430 watts on 6 pins
Edited by obsidian86 - 3/15/11 at 1:16pm
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post #7 of 48
Thread Starter 
Quote:
Originally Posted by obsidian86;12743777 
i dont see the problem even if you got crappy conectors they can handle 250 watts and if you got the good ones you are good for 430 watts on 6 pins

While PCI-E 6-Pin connections can deliver 250W, that entirely depends on rail distribution. On the example I listed in my post, two PCI-E 6-Pin connections share the +12V3 rail which can only supply 16A.
post #8 of 48
And 16 amps on a 12v rail is still 192 watts
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post #9 of 48
Thread Starter 
Quote:
Originally Posted by obsidian86;12749754 
And 16 amps on a 12v rail is still 192 watts

Yes, but without knowing rail distribution, you may use both PCI-E 6-Pin connections from the same rail, and both PCI-E 6-Pin connections would share the 192W.

You would also need to take into account that the combined wattage on the +12V rails is 504W, so you may not even get 192W from the +12V3 rail.

Did you even read my first post tongue.gif
post #10 of 48
a 4 pin is capable of supplying upto 150 watts
a 6pin will allow 200watts.
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