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

xtremetechuk · Mar 15, 2011

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.

obsidian86 · Mar 15, 2011

go learn something useful

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

xtremetechuk · Mar 15, 2011

Quote:

Originally Posted by obsidian86;12740958

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.

Arctucas · Mar 15, 2011

Forgive me, but I am not understanding the point of this?

BinaryBummer · Mar 15, 2011

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.

obsidian86 · Mar 15, 2011

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

xtremetechuk · Mar 15, 2011

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.

obsidian86 · Mar 16, 2011

And 16 amps on a 12v rail is still 192 watts

xtremetechuk · Mar 16, 2011

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

redhat_ownage · Mar 16, 2011

a 4 pin is capable of supplying upto 150 watts
a 6pin will allow 200watts.

mdatmo · Mar 16, 2011

The title implies that there is a danger in using 6 pin to 8 pin adapters, however the OP is about being careful when using multiple pcie adapters from the same 12V rail that isn't rated for enough amps. A clearer title will avoid confusion.

giganews35 · Mar 16, 2011

That is why I love using a single rail PSU.

xtremetechuk · Mar 16, 2011

Quote:

Originally Posted by mdatmo;12750153
The title implies that there is a danger in using 6 pin to 8 pin adapters, however the OP is about being careful when using multiple pcie adapters from the same 12V rail that isn't rated for enough amps. A clearer title will avoid confusion.

Title changed.

I have come across quite a few powersupplys that don't offer any information on rail distribution. Which is why I started a thread on the matter, I thought I was helping, but obviously not.

EPIC FAIL.

obsidian86 · Mar 16, 2011

Quote:

Originally Posted by xtremetechuk;12749957
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

that is why you have protections on a psu to avoid over drawing a single rail

xtremetechuk · Mar 16, 2011

Quote:

Originally Posted by obsidian86;12750996
that is why you have protections on a psu to avoid over drawing a single rail

I agree, however you may be clueless to why the powersupply shuts down. And may mistake the powersupply for being faulty or insufficient, when in actual fact the cause was insufficient amperage to the PCI-E adapter.

obsidian86 · Mar 16, 2011

this is not noobville its overclock.net

xtremetechuk · Mar 16, 2011

Quote:

Originally Posted by obsidian86;12753407
this is not noobville its overclock.net

Yes, and maybe if you read my first post correctly, you wouldn't of made posts trying to correct me, when clearly you were the ignorant one.

I was merely trying help uninformed users of the potential risks when using PCI-E 6-Pin to 8-Pin adapters. I was never expecting immature and vulgar posts from an OCN member that has 120+ REP.

I suggest you grow up.

Redwoodz · Mar 16, 2011

Quote:

Originally Posted by xtremetechuk;12753950
Yes, and maybe if you read my first post correctly, you wouldn't of made posts trying to correct me, when clearly you were the ignorant one.

I was merely trying help uninformed users of the potential risks when using PCI-E 6-Pin to 8-Pin adapters. I was never expecting immature and vulgar posts from an OCN member that has 120+ REP.

I suggest you grow up.

This is also the reason you don't load all the PCI connectors on one rail if you are truly using a multi-rail desgin.Most "multi" rails are really one rail in essence.

Arctucas · Mar 16, 2011

You know, I am still trying to figure out what the risks are?

xtremetechuk · Mar 16, 2011

Quote:

Originally Posted by Arctucas;12754009
You know, I am still trying to figure out what the risks are?

Example -
On multi-rail powersupplys there maybe two PCI-E 6-Pin connections on a single 12V rail, which may only be rated for 15A (180W). While this is perfectly fine for two PCI-E 6-Pin connections (75W+75W). You may not be able to use PCI-E 6-Pin to 8-Pin adapters, as this would exceed the maximum wattage on the 12V 15A rail (150W+150W).

Arctucas · Mar 16, 2011

Quote:

Originally Posted by xtremetechuk;12754167
Example -
On multi-rail powersupplys there maybe two PCI-E 6-Pin connections on a single 12V rail, which may only be rated for 15A (180W). While this is perfectly fine for two PCI-E 6-Pin connections (75W+75W). You may not be able use PCI-E 6-Pin to 8-Pin adapters, as this would exceed the maximum wattage on the 12V 15A rail (150W+150W).

But whether using 6-pin PCI-E connectors, or 6+2-pin PCI-E connectors, there are still only three +12v conductors and three ground conductors connected to the PSU, correct?

xtremetechuk · Mar 16, 2011

Quote:

Originally Posted by Arctucas;12754236
But whether using 6-pin PCI-E connectors, or 6+2-pin PCI-E connectors, there are still only three +12v conductors and three ground conductors connected to the PSU, correct?

Yes, except PCI-E 8-Pin connections have two extra ground connections

PSU manufactures may only abide to official specifications, and wouldn't need more than 15A for two PCI-E 6-Pin connections.

Arctucas · Mar 16, 2011

Yes, but the two extra ground connections are simply connected to two of the existing conductors.

They cannot provide extra amperage.

Alex132 · Mar 16, 2011

6+2 pin = 8pin
ergo 6+2 can provide 150w because its an 8pin

Eagle1337 · Mar 16, 2011

Quote:

Originally Posted by thealex132;12754647
6+2 pin = 8pin
ergo 6+2 can provide 150w because its an 8pin

Except currently the 2 extra pins are used as grounds.

xtremetechuk · Mar 16, 2011

Quote:

Originally Posted by Arctucas;12754555
Yes, but the two extra ground connections are simply connected to two of the existing conductors.

They cannot provide extra amperage.

Correct.

In theory both connections can supply 250W each, however both will be limited to the 12V rail. And as said above, PSU manufactures may only abide to official specifications which is 6-Pin=75w and 8-Pin=150w. So they wouldn't need more than 15A for two PCI-E 6-Pin connections. However the official wattage for two PCI-E 8-Pin connections is 300W, which exceeds 15A (180W).

Hope this helps

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

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