Can the 6 pin gpu power cable in the Mac Pro be used on a 8 pin gpu like a 770?

Discussion in 'Mac Pro' started by Jake0604, Dec 2, 2013.

  1. Jake0604 macrumors regular

    Joined:
    Mar 31, 2011
    #1
    Can the 6 pin gpu power cable in the Mac Pro be used on a 8 pin gpu like a 770?
     
  2. costabunny macrumors 68020

    costabunny

    Joined:
    May 15, 2008
    Location:
    Weymouth, UK
    #2
    I think it depends on the card. Some require all 8 pins to function, whereas others will detect a 6pin and run ok.

    Also be aware that the 6pin mac connector is rated for 75watt max, and the 8pin is usually 150watt so if the card trys to draw 150 through it then there is a risk of damage to the mac's logic board.

    Best ask macvidcards on here as he is the goto guy for this stuff.
     
  3. ActionableMango macrumors 604

    ActionableMango

    Joined:
    Sep 21, 2010
    #3
    This has been hotly debated. Evidence shows that an 8-pin card can pull way more power than the spec safely allows, but many people seem to be doing this just fine with no ill effect so far.

    I can speak personally for a 6+8 GTX 680. It operates just fine with a 6-pin power cable connected directly to the 8-pin socket, no adapter needed. IIRC, the 770 is just a 680 with higher clock rates, so I would expect the same to be true for the 770, but I can't say for sure.
     
  4. gatd, Dec 3, 2013
    Last edited: Dec 3, 2013

    gatd macrumors member

    Joined:
    Jun 2, 2008
    #4
    I'm getting the gtx 680 how many power cables does this need to connect to a mac pro? and which type? it comes with 1x 6pin -6 pin and 1x 6 pin - 8 pin cable
    thanks
     
  5. Gav Mack, Dec 3, 2013
    Last edited: Dec 3, 2013

    Gav Mack macrumors 68020

    Gav Mack

    Joined:
    Jun 15, 2008
    Location:
    Sagittarius A*
    #5
    2x 6pin stock Mini PCie power cables is all that is required for the GTX680 2Gb reference design.

    http://www.ebay.co.uk/itm/Apple-Mac...uting_CablesConnectors_RL&hash=item43b3d5afc0

    If you have a 6+8 you probably have a 4Gb or overclocked version but I believe in nearly all other cases it will fine power consumption wise.
     
  6. gatd macrumors member

    Joined:
    Jun 2, 2008
    #6
    yes it is the 4gb version so what cables will I need if any for the mac pro.
     
  7. pastrychef macrumors 601

    pastrychef

    Joined:
    Sep 15, 2006
    Location:
    New York City, NY
    #7
    Hard to say. Some 2GB models need one 6 pin and one 8 pin power connector and some 4GB models need one 6 pin and one 8 pin power connector.
     
  8. Gav Mack macrumors 68020

    Gav Mack

    Joined:
    Jun 15, 2008
    Location:
    Sagittarius A*
    #8
    Which GTX 680 is it?
     
  9. gatd macrumors member

    Joined:
    Jun 2, 2008
    #9
    eVGA GeForce GTX 680 (4096 MB) (04G-P4-2686-KR) Graphics Card
     
  10. pastrychef macrumors 601

    pastrychef

    Joined:
    Sep 15, 2006
    Location:
    New York City, NY
    #10
    One 6 pin and one 8 pin.
     
  11. gatd macrumors member

    Joined:
    Jun 2, 2008
  12. riggles macrumors 6502

    Joined:
    Dec 2, 2013
    #12
    Some have had success using the two standard 6-pin connectors for the Mac Pro, even on that 8-pin card slot. The concern is too much power being drawn, but you have a non-overclocked reference card design that as spec'd falls below the 225W limit, so you could ver well be fine. Personally, I went with a 670 4GB which has 2x6-pins just to be on the safe side, but that's just me.
     
  13. pastrychef macrumors 601

    pastrychef

    Joined:
    Sep 15, 2006
    Location:
    New York City, NY
    #13
    Some have successfully used 6 pin cables on cards with 8 pin connectors.

    Another alternative would be to look for a card that uses two 6 pin connectors. Zotac and MSI both made cards with two 6 pin connectors.
     
  14. ActionableMango macrumors 604

    ActionableMango

    Joined:
    Sep 21, 2010
    #14
    I have the same card. You need two of these cables:
    http://www.svideo.com/x1900.html

    They are both 6-pin, but that's fine. You won't need an adapter.

    If your existing card in the Mac Pro has one or two cables, like if you had a 5770 for example, you can reuse those.
     
  15. jimj740, Dec 3, 2013
    Last edited: Dec 3, 2013

    jimj740 macrumors regular

    jimj740

    Joined:
    Jul 25, 2013
    Location:
    Pining for the company that once gave us Clarus
    #15
    I think it is time for an electrical engineer's perspective on this...

    It is clear to me that using a video card with either a 6 pin/8 pin combo or a dual 8 pin combo in a mac pro without an auxiliary power supply is exceeding the power budget of the computer and therefore posing some risk of intermittent behavior or possible component damage.

    Does this work acceptably for some people? Sure. there are variations in tolerances and headroom factors that come into play. But there are no guarantees that this will work acceptably for any individual computer. Caveat Emptor!

    There is absolutely NO reason for a graphics card manufacturer to put an 8 pin connector on a card UNLESS it requires more than 75 watts at the connector. The 8 pin connector is more expensive and takes more board real estate. The 8 pin cable is backwards compatible with the 6 pin connector, so there is no concern with the wiring harness of the computer. If you only need 75 watts at the connector, you can plug in either a 6 pin cable or an 8 pin cable.

    It is technically possible to design a card that can sense whether a 6 pin or 8 pin cable is plugged into an 8 pin socket, that is the purpose of the second sense line. It is therefore possible to have the card modify its power profile depending on the cable plugged into it. This however is likely to increase the cost of the card, and therefore unlikely for consumer cards. It is cheaper for the manufacturer to put on the 8 pin connector if they need more than 75 watts at the connection and publish the overall power requirements of the card. If the consumer plugs in the 6 pin cable and disregards the published requirements the manufacturer is not at fault.

    So what is the answer? You should not use a 6 pin cable in a 8 pin socket UNLESS you know that the card supports a modified power profile based on the sense pins. Having said this, the choice is ultimately up to you and you may encounter no problems whatsoever - regardless of the fact you are exceeding the specifications. Or in a worst case (and admittedly relatively low probability) you could fry your motherboard and/or start a fire.

    To put things in perspective, thousands of people exceed the maximum limits for strings of Christmas lights every year. Most people never have an issue. A very small number of people have their homes burn down.

    -JimJ
     
  16. ActionableMango macrumors 604

    ActionableMango

    Joined:
    Sep 21, 2010
    #16
    I stand by my statement for the GTX680 6+8. The reference design GTX 680 is a 6+6 pin card, and actual power measurements revealed by sensors in the Mac Pro prove that sticking an 8-pin connector on there doesn't change the power draw or the performance one bit, whether you supply 6 or 8 pin power to it. Those two extra pins on the connector are about as useful as your appendix.

    You say there's no reason to stick an 8-pin power connector on there, but there are marketing reasons. Overclocker/overvoltage types want MO POWAH. There is also no reason to have fake exhaust tips and hood scoops on a car, but that was a thing too.
     
  17. Gav Mack macrumors 68020

    Gav Mack

    Joined:
    Jun 15, 2008
    Location:
    Sagittarius A*
    #17
    Agreed - the EFI firmware will also scale back any overclock of the PC firmware has to the stock mac edition EVGA card. Which means the only additional power from a 2gb will essentially be just powering the extra video ram.

    I flashed pretty much the identical card in appearance, possibly exactly the same to the OP card when I installed a 4gb GTX 680 along with a pair of updated quad core chips in a 5,1 only last week. Used only a pair of 6 pin leads and they've given it more than a heavy stress test using CUDA to make sure it all works fine.
     
  18. jimj740, Dec 3, 2013
    Last edited: Dec 3, 2013

    jimj740 macrumors regular

    jimj740

    Joined:
    Jul 25, 2013
    Location:
    Pining for the company that once gave us Clarus
    #18
    Just to clarify: the ONLY purpose of the two extra pins on the 8 pin connector are to indicate that the board may safely draw up to 150 watts on the connector. The connectors are specifically keyed to be compatible, the actual power lines between them are identical, and the cables themselves are capable of far larger loads. The board designer can choose whether or not to respond to this information, and this will vary from design to design. It is incorrect to draw a broad conclusion based on the single sample of one design.

    And to be clear: I am not arguing, nor trying to prove myself correct. A combination is either within specifications or it is not. Many, many systems operate outside of specification. Whatever choices anyone makes given this information are entirely their own responsibility.

    [Edit/addition]
    In the specific case of the GTX 770, the overall power specification of 230 watts is very slightly above the maximum specified of 225 watts. If there were a way to guarantee that power was drawn equally from the slot and the two connectors there would be a very, very slight probability of failure. Without analyzing the circuit, there is no way to know where the card will actually draw its power - the card's design could legitimately draw 150 watts from the 8 pin connector, although that is unlikely. It is also unlikely that the power draw is equal across both connectors and the slot...


    [second edit/addition]
    It is clear reading the other threads on this topic that there are some basic misunderstandings of circuit design. The multiple power sources are not a "pool" to draw against. People are surprised at the uneven power draw from the various sources when they bother to measure... this is by design!!! For practically all consumer designs, each component on the board that requires power will be assigned to a single power source - this will not change over time. Components will NOT draw from multiple sources; think of it as three separate power circuits on the board. This is why it means nothing to say that the reference design uses two 6 pin connectors, so the non-overclocked boards that use 6+8 pin connectors should work. Unless these cards were laid out with the same chips assigned to the same connectors, they could have vastly different distributions of power. The board's designer is within specification to put whatever combination of chips he chooses on the same power connector as long as he does not exceed it's specification. So a non-overclocked non reference version of a 225 watt card in the 6+8 config could draw 145 watts on the 8 pin, 5 watts on the 6 pin, and 75 watts on the slot pins if the designer wanted to. And it is also clear that in the other threads that have actual measurements, people have observed in excess of 125watts drawn on the 8 pin connector - this is far beyond the "headroom" of a typical design for a 75 watt circuit. And to be explicit: I have no idea what the actual headroom is for the Apple motherboard. This may or may not be a serious issue.

    As to the "it works on my machine" comments - I do not dispute this - I believe you. When designing for mass production, desired failure rates are on the order of 1 per multiple thousands of units (depending on the volume, this can be 100s of thousands). As long as you don't go hog wild, the odds are greatly in your favor - but SOME machines will fail.

    Perhaps another analogy - your car's engine has a redline. The engine will not blow up if you exceed the redline slightly occasionally. Some engines can exceed the redline regularly and for sustained periods. And like the circuits, the probability of failure is related to how far you exceed the limit, and for how long, and in what environment, and with what cooling. Would you think it good advise to tell people to ignore the redline because you exceeded it and your engine didn't blow up? Just like the redline the power specification is there for a reason - reasonable statistical confidence levels of longevity over sample pools of multiple thousand units.

    Personally I don't care one way or another about what someone does with their own machine... I'm only hoping to help people make informed choices.

    -JimJ
     
  19. gatd macrumors member

    Joined:
    Jun 2, 2008
    #19
    according to the pdf for the 680 4gb it says

    550 watt or greater power supply with a minimum 38 amps on the +12 volt rail.
    one 6-pin PCI Express power connector or two available hard disk power connector and one 8-pin PCI Express power connector or two available 6-pin PCI Express power connectors.

    so is that three 6-pin power connectors?
     
  20. Gav Mack macrumors 68020

    Gav Mack

    Joined:
    Jun 15, 2008
    Location:
    Sagittarius A*
    #20
    Two 6 pin PCIe power connectors will do the job fine. I'm sure if you ask MacVidCards who has probably sold dozens of them here or ask others on the netkas forum:

    http://forum.netkas.org/index.php/board,6.0.html

    You'll get the same answer!
     
  21. fifthmanstandin macrumors member

    Joined:
    Jul 11, 2009
    #21
    Ok so I just bought this card

    http://www.newegg.com/Product/Product.aspx?Item=N82E16814130932

    The manufacturer page says it's a 170 watt card

    http://www.evga.com/Products/Product.aspx?pn=02G-P4-2765-KR

    My questions is can I use a mini 6 pin pcie to 8 pin pcie cable on the motherboard in conjunction with a second 6 pin pcie cable to power the card, currently I've got two molex connectors adapted to a 6 pin and two six pins adapted to an 8 pin to power the card. Nothing is available to power my dvd drive now.

    I was going to buy this :

    http://www.amazon.com/PCIe-Power-Cable-nVidia-Video/dp/B0045Q8F84/ref=pd_sim_e_2

    to remedy that issue. now I'm worried.
     
  22. riggles macrumors 6502

    Joined:
    Dec 2, 2013
    #22
    How many different threads are you going to post the same questions in? Take a minute and read the existing threads. You should be fine with 2 standard 6-pin cables. Just use the one that came with your MP and this additional one from OWC and skip the adapters. Done. No more worrying.
     
  23. fifthmanstandin macrumors member

    Joined:
    Jul 11, 2009
    #23
    Yeah see I read the existing thread and the problem I have, that I would like to verify, as is the purpose of this place, is that is is has been said that if a manufacturer places an 8 pin slot on a card it does so for a reason. I has been suggested to me to use an external power supply to power the card, that the two six pin connectors will be fine, that two six pin connectors will not be fine, that an 6 pin and a six pin mini to 8 pin would be fine and all contradictions in between. So I'm posing the question for my specific card to get more specific information since the card in question by the OP is not a factory overclocked card, as mine is. So if you don't mind I'd like someone or several people to weigh in on this before I change the current configuration and risk burning the card, the comp or my house. I feel like that's a reasonable approach. Especially since two of the members who have helped me quite a bit are already posting on this thread.

    Given that the PSU on this mac pro is, as I understand it, 980 watts and my card, according to the manufacturer, requires 175 watts and I have no idea how much the rest of the system is taking I have no way of knowing at this time if the card is drawing too much to begin with. The previous posts lead me to believe also that by not doing a 6 and 8 pin connection that I would be either powering less of the ram or less card somehow.
     
  24. ActionableMango macrumors 604

    ActionableMango

    Joined:
    Sep 21, 2010
    #24
    I agree with you, but I don't understand the long lecture replies. Am I making broad conclusions? Every single reply I've made in this thread, I specifically mentioned the GTX680 6+8.

    Gatd in particular asked specifically about the GTX680 6+8. I don't want him getting worried about it. That setup is completely 100% within the power specifications. It's been verified using the MP's internal power sensors.

    The 770, being merely a rebranded overclocked 680, will almost certainly be the same. Heck, it's been measured that official, supported 6+6 cards sold by Apple for use in the MP far exceed the 680's power draw, and even far exceed the 75W-per-connector PCIe power specification on one of the connectors!
     
  25. TheDoc macrumors member

    Joined:
    Mar 18, 2008
    #25
    Here's my completely untechnical understanding:

    You're allotted 225 Watts of power for a GPU: 6-Pin x 75W, 6-Pin x 75W, PCI x 75W. If you get a card that is close to that (say, 220 TDP), you might want to consider an external PSU. If your card's TDP is *over* 225W then you definitely *need* an external PSU.

    Since the card in question has a TDP of 175W you should easily be covered by what the Mac Pro is already providing (225W).
     

Share This Page