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Can I just plug a six-pin connector into GPU's 8-pin input with a decent PSU?

Ichinisan

Lifer
Oct 9, 2002
28,158
1,170
136
Not sure if I should ask this here, or in the "Video Cards and Graphics" forum.

Are some GPUs smart enough to detect when a 6-pin PCI-E provides adequate power for an 8-pin connector?

I have an older-version PC Power & Cooling TurboCool 1KW which has only 6-pin connectors. It's hard enough to manage the cables as it is and an extension/ adapter would just make things more cluttered.

Basically, I'm asking if some GPUs allow you to use a 6-pin PCI-E power lead on an 8/pin GPU connection, leaving two of the pins unoccupied.

It's a single 12v rail design, so I know that the 6-pin connectors are capable of providing as much power as needed.

The power supply is overkill, I know:
-Intel Core i7 860 CPU
-MSI P55-GD55 motherboard
-A-Data 4GB DDR3-1600 (2x2GB) RAM
-BFG NVIDIA GeForce GTX280 GPU
-WD 2TB Green 64MB Cache WD20EARS HDD (to be replaced w/ 7200RPM HDD)
-PC Power & Cooling TurboCool 1KW PSU
 
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Modelworks

Lifer
Feb 22, 2007
16,243
5
76
All the 12VDC pins on both the 6pin and 8pin connectors are connected on the video card so it doesn't know the difference. The reason for 8 wires vs 6 wires is because as current increases you need larger wire. They could do it with 2 wires but then the wires would be larger and harder to maneuver in the case. So instead of using only 2 large wires they use multiple smaller wires.
 

fffblackmage

Platinum Member
Dec 28, 2007
2,548
0
76
The 6-pin PCI-E power connector specification includes two 12V wires and three ground wires and has a rated maximum power output of 75W. The 8-pin includes three 12V wires and 5 ground wires and has a rated power output of 150W. source

Because the 6-pin specification only specifies two 12V wires are required, you might not be able to provide enough power. However, some power supply designs actually include the third 12V wire in the 6-pin connector anyways. In that case, there isn't much difference between the 6-pin and 8-pin, other than the two additional ground wires.

You should check out the manual for your graphics card to see if you can just use the 6-pin, though I'm not sure if any graphics cards allow that.

My 4890's manual warns against using the 6-pin in the 8-pin socket. I didn't know that at first and tried it anyways, but it doesn't work, and fortunately, I didn't fry anything. It just complain about not having enough power.
 

Modelworks

Lifer
Feb 22, 2007
16,243
5
76
The 6-pin PCI-E power connector specification includes two 12V wires and three ground wires and has a rated maximum power output of 75W. The 8-pin includes three 12V wires and 5 ground wires and has a rated power output of 150W.

Incorrect. You need the same amount of ground wires as +V wires . 6 pin is (3) +VDC and (3) GND, 8 pin is (4) +VDC and (4) GND. If you used 2 +V wires and 3 GND wires on a connector the 3rd GND is pointless as nothing can flow into the circuit greater than what the 2 +V wires supply.

If you buy a supply that only has 2 yellow wires on the 6 pin connector , take it back
 

fffblackmage

Platinum Member
Dec 28, 2007
2,548
0
76
Incorrect. You need the same amount of ground wires as +V wires . 6 pin is (3) +VDC and (3) GND, 8 pin is (4) +VDC and (4) GND. If you used 2 +V wires and 3 GND wires on a connector the 3rd GND is pointless as nothing can flow into the circuit greater than what the 2 +V wires supply.

If you buy a supply that only has 2 yellow wires on the 6 pin connector , take it back
I'm guessing the extra ground wires is part of a safety design, such as paths to ground for some random discharges that might occur. Someone randomly touching something they're not supposed to... lightning... shorts... I'm not really certain.

The specifications I've been seeing is that the two 12V wires are required for the 6-pin PCI-E, but the third is only optional. source1 source2 source3

8-pin only has three 12V wires and 5 ground wires.

Three yellow 12V wires and 5 black ground wires. The extra two wires on the 8-pin are just ground wires. The difference is that the 8-pin requires the third 12V wire.
 
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Mark R

Diamond Member
Oct 9, 1999
8,517
13
81
The 6-pin PCI-E power connector specification includes two 12V wires and three ground wires and has a rated maximum power output of 75W. The 8-pin includes three 12V wires and 5 ground wires and has a rated power output of 150W. source

The 8 pin connector includes:
3 12V wires
3 Ground wires
2 connector detection wires (1 is on the same row as the other 3 grounds on the 6-pin connector - and allows the card to detect whether any connector is plugged in. 1 is on the opposite row - this tells the card, an 8 pin connectors is plugged in).

If Neither detection pin is connected - the card operates in 'no auxillary power mode'
If the ground row one is connected - the card operates in '6 pin power mode'
If the opposite row one is connected - the card operates in '8 pin power mode'
 
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Mark R

Diamond Member
Oct 9, 1999
8,517
13
81
I'm guessing the extra ground wires is part of a safety design, such as paths to ground for some random discharges that might occur. Someone randomly touching something they're not supposed to... lightning... shorts... I'm not really certain.
The 6 pin connector has the following connections:
2 12V
2 Ground
1 Connector detection (connect to ground to tell card that connector is present)
1 Optional 12 V

The specification intends that graphics cards check the middle ground pin for the presence of a ground connection. If this is connected, then the card should activate the auxillary connection - otherwise, the card should operate on slot power only.

This arrangement means that the middle ground can't be used as a power connection. As a result the 6 pin connection was designed so that the power could be safely carried by 2 pins in each direction. The 3rd 12V pin is therefore not required - but could be used, if desired, in order to marginally improve power quality.
 

fffblackmage

Platinum Member
Dec 28, 2007
2,548
0
76
The specification intends that graphics cards check the middle ground pin for the presence of a ground connection. If this is connected, then the card should activate the auxillary connection - otherwise, the card should operate on slot power only.

This arrangement means that the middle ground can't be used as a power connection.
Oh, didn't realize power and detect couldn't be on the same pin. Good to know! Thanks!
 

hamunaptra

Senior member
May 24, 2005
929
0
71
You know, I am wondering, since the PSU is a single rail design, I wouldnt see much problem with using molex to PCIE 6 pin and then PCIE 6 pin to a 8pin adapter. I could see how this would be a huge issue with multi rail PSU's but your should do fine. Or if you have 2 extra PCIE6 connectors to begin with could just use the 2x 6pin to 1x8 pin adapter.
 

CZroe

Lifer
Jun 24, 2001
23,643
635
126
Even though the rail can deliver it the wire gauge may not tolerate the extra amps and would get hot and resistance would increase. I think an adapter that supplements them off the 4-pin connectors would be best. I guess it would also help with detection.
 

beany323

Senior member
Jan 11, 2005
492
0
0
I'm guessing the extra ground wires is part of a safety design, such as paths to ground for some random discharges that might occur. Someone randomly touching something they're not supposed to... lightning... shorts... I'm not really certain.

The specifications I've been seeing is that the two 12V wires are required for the 6-pin PCI-E, but the third is only optional. source1 source2 source3

8-pin only has three 12V wires and 5 ground wires.

Three yellow 12V wires and 5 black ground wires. The extra two wires on the 8-pin are just ground wires. The difference is that the 8-pin requires the third 12V wire.
so my old video card uses 6 pin power supply x 2. (for each car) it has the above one on one of the wires.

can i use that for a 8 pin or..thanks in advance.
 

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