GPU power supply requirements

Tyrant89

Reputable
Dec 11, 2015
3
0
4,510
Ok, so im sorry if this has already been posted but i find mixed discussion on the topic.

I'm fortunate enough to have a spankin new GTX 980TI Lightning.

I recently upgraded to an Acer Predator (27 in 144hz 1440P with G-Sync). Since then i have had all kinds of issues with games freezing up (Fallout 4 and Metro).

After hours of different attempts at fixing the issue i finally read a post that suggested i had the GPU powered incorrectly.

The LIGHTNING (as far as i know) is the only 980Ti that requires TWO 8 AND one 6 pin power connections.

The suggestion was that i needed to have individual power cables connected to my PSU. I have previously read that it is OK to use a Power cable that connects 8 pins to the PSU but then splits into an 8 (6+2) and a 6 pin. Once i connected a separate cable to each connection (so a total of 3 separate cables) my crashing and stalling issues went away.


So my question is...
why is there so many people suggesting that it is ok to use a split 12V power cable that has a 6+2 AND a 6 pin when it seems to become a problem when you try to use 1440p monitors vs. 1080p.

I have actually seen an increase in FPS since i made this change. so i guess the only other problem is that my PSU only has 4 power slots so if i SLI in the future i am going to have to hope they make PSU's that have 6.


Any help understanding these GPU power cables would be awesome. Why do they even make a power cable that has an 8 (6+2) and a 6 if only one should be used at a time.

Link to my build:
http://pcpartpicker.com/b/6F2RsY
 
Solution
The only time I have seen a 8 pin to 6 pin plus 6+2 pin is with EVGA. Boneheaded idea.

The 8 pin and 6 + 2 pin are rated for 150 watts
The 6 pin is rated for 75 watts.

So how do you pull 225 watts of power at the card end of the cable when the PSU end of the cable is rated for onlyy 150 watts ?

When doing a build for someone with an EVGA PSU I immediately wrap them with tape that says "NEVER EVER USE THESE"
The only time I have seen a 8 pin to 6 pin plus 6+2 pin is with EVGA. Boneheaded idea.

The 8 pin and 6 + 2 pin are rated for 150 watts
The 6 pin is rated for 75 watts.

So how do you pull 225 watts of power at the card end of the cable when the PSU end of the cable is rated for onlyy 150 watts ?

When doing a build for someone with an EVGA PSU I immediately wrap them with tape that says "NEVER EVER USE THESE"
 
Solution
You have a single +12 volt rail PSU then it is OK to run one cable to two connectors. That single cable call handle all the amps the GPU pulls through two connectors! Why it did change on yours I do not have a clue. If the PSU is multi rail there would be the limit on the rail that would warrant more cables.
If the cable could not carry the amps needed it would over heat and catch fire!
 


8 pin cables / connectors rated only for 150 watts; how you pull 225 watts from the other end w/o exceeding cable's rating ? Counting amps per wire, there should be a lot more capacity (288 as I recall .... 3 x 12v x 8 amps which is just enough to carry the 225) but from warranty perspective, I wouldn't recommend exceeding the "rated" capacity.



 


Because the cable can carry more watts than a 8pin connector is delivering! 150watts / 12V = 12.5 amps a single 14 gauge wire will handle it, on all 8 (6+2) connectors I have seen there is at minimum 3 + wires and 3 grounds run from the PSU.
 
Yes, we all know that PSUs can deliver more than their rated power but that doesn't mean that I will recommend that my users pull 690 watts from their 650 watt PSUs. We all know that ya can pull more than 1 amp from a MoBo fan header (I ran 8 x 0.14 amp fans for 6 weeks) but that doesn't make it a "recommended" procedure and I wouldn't ask for an RMA is I blew the header.

As I had indicated:

Counting amps per wire, there should be a lot more capacity (288 as I recall .... 3 x 12v x 8 amps which is just enough to carry the 225) but from warranty perspective, I wouldn't recommend exceeding the "rated" capacity.
 


I am just talking about the wire to the connector that can carry more than the connectors needs! EVGA is not the only company that does this and nobody would if there was a danger of the wire overheating and burn down the house! Put into perspective, how many people have power strips that they plug into a single socket in their home but have 6 or more plug ins!
 
I understand what the cable are capable of but also would never recommend exceeding rated capacities for warranty concerns alone. 14 gauge will handle it .... but how many PSU manufacturers are using 14 gauge, most are using 18 or 16 on the high end units. And the connector rating is different from the cable rating.

http://www.tomshardware.com/reviews/power-supply-specifications-atx-reference,3061-12.html

All ratings assume Mini-Fit Jr. connectors using 18-gauge wire under standard temperature conditions.

http://www.overclock.net/t/1084225/psu-wire-gauge

Wires on quality PSUs are minimum 18AWG, on quality units sometimes 16AWG for the main power cables. On cheap-o crap, 20AWG.

http://www.playtool.com/pages/psuconnectors/connectors.html#pciexpress8

The PCI Express 2.0 specification released in January 2007 added an 8 pin PCI Express power cable. It's just an 8 pin version of the 6 Pin PCI Express power cable. Both are primarily used to provide supplemental power to video cards. The older 6 pin version officially provides a maximum of 75 watts (although unofficially it can usually provide much more) whereas the new 8 pin version provides a maximum of 150 watts. It is very easy to confuse the 8 pin version with the very similar-looking EPS 8 pin 12 volt cable
.

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

If you don't have an 8 pin 12 volt cable then you can use the adapter shown above. It converts a couple of 4 pin peripheral power cables into an 8 pin 12 volt cable. If you use one of these adapters then be sure to plug the 4 pin peripheral connectors into separate cables coming from the power supply. If you plug them both into the same power supply cable then you are drawing all the power of the 8 pin 12 volt connector through a
single 18 gauge
wire. You can often get away with that but there's no reason to do it.

Also Cablemod replacement wires for EVGA PSUs are also notably thinner than the OEM stuff.
 
Single 18gauge is good for 9.5 amps minimum 3 cables feeding dual PCI'e connectors = 28.5 amps = 342 watts the wires for the second connector are parallel connected out of the wires in 150watt 8 pin connection so the math PSU manufacturers make checks out.
 

Tyrant89

Reputable
Dec 11, 2015
3
0
4,510



Thanks for the response!

I feel like the fact that my GPU is one of the only cards with a (8, 8 AND 6) i might be more exposed to issues than others have in the past.

What I find really interesting is that i didn't have this problem on my 1080p monitor. I would have thought that running Valley or Furmark would have caused the issue regardless of G-sync or 1440p. Also, i usually only get this issue in actual games. Valley Ran for an hour on my new monitor with problems.


Best part of this post so far is the validation that there are lots of differing opinions on the topic. Half the comments "yay" half the comments "nay"
 

Tyrant89

Reputable
Dec 11, 2015
3
0
4,510


Thanks for the response. I liked the link as well.
 


I gave ya the correct math in the 1st post - 288 watts (3 x 12v x 8 amps)

http://www.tomshardware.com/reviews/power-supply-specifications-atx-reference,3061-12.html

The six-pin connector uses two +12 V wires to carry up to 75 W, whereas the eight-pin connector uses three +12 V wires to carry up to 150 W. Although these figures are what the specifications allow, the wires and terminals of each connector are technically capable of handling much more power. Each pin in the PCI Express auxiliary power connectors is rated to handle up to 8 amps of current using standard terminals—



What I am saying is regardless of the wire's capability, the cable is the sum of various parts .... that included the connectors at both ends and has an allowance for the resistance from oxidation that can build up at the connection points (plug / socket) ... not all PSU manufacturers use gold contacts. There is a reason that they rate the cables at what values they are assigned. A factor of safety is applied to establish headroom.... the same reason we limit our overclocked core temps 20C or more below TJmax.

The "house on fire" analogy isn't applicable here and one is suggesting that will happen. But..... for example

I see Jonnyguru test results showing that my 1250 watt rated PSU can handle 1417 watts no problem, but I would not recommend putting 4 overclocked Fury's on it and running it up there during gaming sessions.

Just because I can take 6 aspirins at a time w/o dying doesn't make it recommended practice.

My car engine won't die if I go 20% past the recommended oil change interval, but if the changes are done by the dealer and you bring it in at 75,000 miles asking for warranty repairs under your 100k warranty, expect a battle.

Highways are designed fro much higher speeds than the actual speed limits placed upon them.

A 1,000 pound wire rope hoist will have a cable with a breaking strength of 4,000 pounds .... but use it to lift a 1,500 pound load and it's an OSHA violation.

So no, while there's not likely to cause a fire and burn down the house as you put it.... I wouldn't recommending putting more watts thru a cable that people, with much more knowledge and experience than I possess, have assigned a "safe" rating of 150 watts. As a system builder, I'd hate to have to walk into small claims court to defend a claim from a customer whose system failed; I wouldn't want to explain to the judge that I knew better than those who wrote the ATX specification and that there was no problem pulling wattage 50% above the rating established by the applicable standards organization.