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Author Topic: Why do they even require two pcie power slots in a video card???  (Read 25307 times)
gigabytecoin
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May 21, 2011, 12:06:58 PM
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This doesn't make any sense to me from an engineering perspective...

I have a PSU that is rated for 850W gold+, it is non modular and only has 4 pcie 6+2 pin power cables...

So WHY do I have to purchase a 6 pin to 6+2 pin dual pcie power cable splitter only to recombine the power inside of the GPU???

I mean really... one cable transfers all of the power from the psu to the video card... I split it into two cables (cost of ~$10 USD)... and then assumably the video card recombines that power and uses it for whatever it pleases...

Why don't all video cards just have one 6 pin power plug?
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WesleyK
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May 21, 2011, 12:28:56 PM
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Because you cannot transfer that amount of current through only 6 wires. The wires will simply overheat.
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May 21, 2011, 12:38:02 PM
 #3

Because you cannot transfer that amount of current through only 6 wires. The wires will simply overheat.
its popular myth.
in today implementation only six wires used in 8-pin Aux PCI-e cord. meaning they had same avg/power capacity cable and [calculated]they safety enough for nowday's GPU's you can safely use 6pin-8pin bridge.
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May 21, 2011, 04:24:03 PM
 #4

It also gives you the option of distributing the load across different rails. 

If you're searching these lines for a point, you've probably missed it.  There was never anything there in the first place.
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May 21, 2011, 05:21:03 PM
 #5

There is a limit to the amount of power you can draw on a given rail/connector. The 6 pin PCI-e power connector specification is rated for up to 75 W, as is the PCI-e slot itself, so you need more than one to power any card that draws over 150W. The 8-pin PCI-e connector is rated to 150W, but not all PSUs have these, so manufacturers have use two 6-pin connectors if possible. Obviously, any card that draws more than 225W will need to use 8-pin.

Here's a good link that explains it in more detail:

http://www.playtool.com/pages/psuconnectors/connectors.html
Basiley
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May 21, 2011, 05:23:00 PM
 #6

There is a limit to the amount of power you can draw on a given rail/connector. The 6 pin PCI-e power connector specification is rated for up to 75 W, so you need more than one to power most graphics cards. Here's a good link that explains it in more detail:

http://www.playtool.com/pages/psuconnectors/connectors.html

its only theory.
nowdays GPU's not use it, getting power from 6-pins even from 8-pin socket.
ans same was true for some "noname" PSU's too.
and when you check current GPU's power consumption and this avg-PCi-e-power-cable specs you can see, thats that reasonable, cuz 6-pin specs power capacity exceed very slightly and wires never go even warm.
Tyran
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May 21, 2011, 05:37:20 PM
 #7

So WHY do I have to purchase a 6 pin to 6+2 pin dual pcie power cable splitter only to recombine the power inside of the GPU???
Wait, are you trying to power a graphics card that requires 2 connectors by splitting a single one?
While it's true that PCIE connectors can deliver far more than what they're specced for, I don't think going 100% over the spec is a good idea. There's a reason the card needs 2 connectors.
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May 21, 2011, 05:41:53 PM
 #8

So WHY do I have to purchase a 6 pin to 6+2 pin dual pcie power cable splitter only to recombine the power inside of the GPU???
Wait, are you trying to power a graphics card that requires 2 connectors by splitting a single one?
While it's true that PCIE connectors can deliver far more than what they're specced for, I don't think going 100% over the spec is a good idea. There's a reason the card needs 2 connectors.
if he' just lack of extra 6-pin PCI-e out from powerful enough PSU[which is unlikely, cuz all reasonably-rated had two at least] its okay.
but when/if he's try to power card from splitted 6-pin-->2x6-pin or molex-->6-pin  things from weak PSU, things can go bad very quick. with noise[explosive and somewhat dangerous. really]and smoke/burn and both PC owner and PC permanent dammage.
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May 21, 2011, 05:59:02 PM
 #9

if he' just lack of extra 6-pin PCI-e out from powerful enough PSU[which is unlikely, cuz all reasonably-rated had two at least] its okay.
Well, it's common knowledge that the 6 pin connectors that are specced for 75W can safely deliver 150W+. People use 6->8 pin adapters all the time and as you already said, the 6+2 pin connectors only add 2 more ground wires. However, if you're connecting a power hungry card like a 5970 to a single line, you're going to be drawing up to 225W from that (more if overclocked). I'm not sure if that's still within safe limits (the wires probably won't overheat, but the connector could get damaged at the point where you're splitting it).
If you still want to risk it, you should also check if your PSU can deliver that much on a single rail.
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June 29, 2013, 01:25:50 AM
 #10

if he' just lack of extra 6-pin PCI-e out from powerful enough PSU[which is unlikely, cuz all reasonably-rated had two at least] its okay.
Well, it's common knowledge that the 6 pin connectors that are specced for 75W can safely deliver 150W+. People use 6->8 pin adapters all the time and as you already said, the 6+2 pin connectors only add 2 more ground wires. However, if you're connecting a power hungry card like a 5970 to a single line, you're going to be drawing up to 225W from that (more if overclocked). I'm not sure if that's still within safe limits (the wires probably won't overheat, but the connector could get damaged at the point where you're splitting it).
If you still want to risk it, you should also check if your PSU can deliver that much on a single rail.

This safe?



Melted plugs lead to non connected contacts which heats up the rest of the pins more and things can burst into flames.
tom_o
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June 29, 2013, 03:34:10 PM
 #11

Holy old threads!

The reason for multiple power connectors on larger GPU's has not so much to do with the wire I2R losses, but the spring contact I2R losses of the PCI-E power connector.  Your picture demonstrates the reason fairly clearly.  3 pairs of 18 AWG wire could carry > 75A@12V (900W) at the conductor lengths in most ATX PSU's without posing a fire hazard based on the insulation temperature ratings.  Hope it didn't do any major damage otherwise!

Personally, I always make sure it's connected (1) 12V rail per GPU for this reason as well, it is more likely to ensure an equitable wattage split between the connectors and conductors involved.

Oops not sure how I did that, just scrolled up thinking I wonder who necrod this then?  Embarrassed Tongue
Trillium
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June 30, 2013, 11:01:23 PM
 #12

Take 100 (one hundred) Radeon 7990's. Overclock cores. Overclock memory. Increase voltages.

Now mine scrypt coins for 1 week on all of them.

Record number of cables on fire.

SCIENCE!

BTC:1AaaAAAAaAAE2L1PXM1x9VDNqvcrfa9He6
Rakessh
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February 08, 2014, 03:17:39 PM
 #13

Take 100 (one hundred) Radeon 7990's. Overclock cores. Overclock memory. Increase voltages.

Now mine scrypt coins for 1 week on all of them.

Record number of cables on fire.

SCIENCE!


-
Gator-hex
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February 09, 2014, 01:08:38 AM
 #14

if he' just lack of extra 6-pin PCI-e out from powerful enough PSU[which is unlikely, cuz all reasonably-rated had two at least] its okay.
Well, it's common knowledge that the 6 pin connectors that are specced for 75W can safely deliver 150W+. People use 6->8 pin adapters all the time and as you already said, the 6+2 pin connectors only add 2 more ground wires. However, if you're connecting a power hungry card like a 5970 to a single line, you're going to be drawing up to 225W from that (more if overclocked). I'm not sure if that's still within safe limits (the wires probably won't overheat, but the connector could get damaged at the point where you're splitting it).
If you still want to risk it, you should also check if your PSU can deliver that much on a single rail.

This safe?



Melted plugs lead to non connected contacts which heats up the rest of the pins more and things can burst into flames.

Yep, there's definitely a reason why they invented American Wire Gauge (AWG) and took the time to stamp it on all your PSU cables!  Wink

googie4
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February 09, 2014, 08:25:30 AM
 #15

Why care?
DrG
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February 09, 2014, 08:50:50 AM
 #16

Easy to way to weed out the simple minded miners who have no business mining - roasting your nuts on your rig.

Trillium
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February 09, 2014, 09:49:24 AM
 #17

Why care?

Starts a fire and destroys everything you own? (Hope you had insurance.)

Even with insurance it'll work out to be a huge loss of your time and your money because there are always unforeseen costs that weren't considered.

That's why we care.

BTC:1AaaAAAAaAAE2L1PXM1x9VDNqvcrfa9He6
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