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Hot!GPU Power: One cable, One connection; no splitter cables.

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Intoxicus
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2020/12/03 12:30:26 (permalink)
Saw a top level post on r/Nvidia where someone fried their 3000 series GPU by using a splitter cable for GPU power.

DO NOT USE BOTH SPLITTER CABLE CONNECTIONS FOR GPU POWER!!!
Imho they should not even exist and are more trouble than they add value. It should be one cable, one connection for GPU power.

Supposedly a splitter should be fine with a 2070. Except that before I got my 3080 I had a 2070 that had instability issues on a power splitter cable. I went one cable, one connection and it all cleared up. That was on a 1000W EVGA Supernova G3 Gold. For the 2070 there was more than enough power available from the PSU. The splitter cable though seemed to limit the power enough to cause issues.

For the 3000 series I would never, ever, use the splitter on a splitter cable. One cable, one connection is my personal rule for GPU power. If you only have splitters available then only use one of the connections and cable manage the hanger.

One of the troubles is the connections are not rated for as much power draw as the cable. Sure you have two connectors GPU to split that load. *Trouble is at the PSU side you only have one connection and both GPU connectors drawing too great a load will exceed the rating for the PSU side connection!* (If an actual Electrical Engineer has more input and/or any corrections please drop in with some math and stuff.)

I see my 3000 series goes right up against the 400W power limit at max loads. I don't feel safe using both connections on a splitter seeing that power draw.
And that's not even the 450W power limit BIOS I haven't got around to trying out yet!

If you are running that 450W power limit BIOS on a 3080 using both connections on a splitter don't be surprised if your OC is limited and you get crashes and instability.

Even if you technically can use both connections on a splitter should you? 
If it's more ideal and yields better results to go one cable, one connection then why not just go one cable, one connection anyway...

"Humans are not rational animals, humans are rationalizing animals." -Robert A Heinlein
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    Intoxicus
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/03 14:08:50 (permalink)
    So doing some research it seems the 225W rating for the cables might be a misunderstanding. 
    It seems people are getting that from the 150W connector limit added to the 75W from PCI-E.
    Which if that is the case means you're only getting 150W from an 8 pin PCI-E cable. Not 225W.

    Which means at 150+150+75 you're 25W short of the 400W power limit using a splitter power cable on a 3 X 8 Pin 3080.

    The splitter may be rated for 150W at the connections sure. But can the cable itself handle that?

    Even if the cable could support 225W why push the limits on power connections and cables? It seems like an unnecessary risk for 0 benefit.


    post edited by Intoxicus - 2020/12/03 14:15:56

    "Humans are not rational animals, humans are rationalizing animals." -Robert A Heinlein
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    Hoggle
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/03 14:37:48 (permalink)
    It’s always best to use separate cables but a standard does exist. It should be perfectly safe with a quality PSU so while I can see stability issues for an overclock it should be ok at stock.

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    kougar
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/03 22:38:57 (permalink)
    The poster in question showed a photo of their PSU, and it was clear the PSU was designed with no less than FOUR outputs for PCIe cables. If the PSU is designed to split the load across multiple cables then it's always best to do so. Yes there are standards, but in the real world connectors do not always have good contact, whether that is due to oxidation or because the physical pins no longer perfectly match up.
     
    Case in point, I once had a 980X slag an EPS12v connector. It wasn't caused by extreme load, but by poor pin contact that increased the natural resistance until the connector began to scorch. It's always best to divide the load across multiple cables when at all possible just in case, because connectors do wear out over time and with use. When dealing with high-power electronics like a 3090 there's no sense not taking every precaution ahead of time to prevent issues later.   
     
     


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    Intoxicus
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 08:59:16 (permalink)
    Here's a copy pasta of a comment I made in Reddit when someone asked is there data to support my position:

    Yes, the 8 pin connectors are rated for 150W.
    6 pin connectors are rated for 75W.
    PCI-E delivers 75W through the slot.
     
    That is easy to find and reference info, it's even on wikipedia. Some of the info is fundamental electronics and electrical engineering. I am not an electrical engineer myself, but my dad is and I grew up doing this stuff. You can ask an electrical engineer to fact check me and if I am wrong I would truly like to be respectfully corrected.
     
    https://www.gpumag.com/gpu-power-connectors-explained/
     
    https://en.wikipedia.org/wiki/PCI_Express#Power
     
    It takes a bit of digging but you can find the engineering specs if you really want to go that deep. I found a bunch for PCI-E(PCI-E publishes them all,) but still trying to find some PSU engineering spec sheets currently.
     
    Also Buildzoid has an excellent video that talks about this where he specifically says daisy chains should be fine unless we get into 400W territory. That video is 3 years old and was made before we even had 2000 series.
     
    https://www.youtube.com/watch?v=9nM80JmzKvc
     
    If you have a Daisy chain with connectors rated at 150W and the cable can handle more you have an issue at the PSU side. The PSU can only safely draw 150W through it's single connection and somehow deliver more than 150W to two 8 pin power connectors at the GPU. Electricity does not magically increase amps and volts to make more watts. Actually because of resistance and voltage drop you get less than you asked for in the form of less voltage and the same(or more) current(amps.) This creates heat at the connectors, unused or inefficient electricity turns into heat.
    Also lets remember you're NOT getting 100% efficiency(that's almost impossible) and you're not going to get the full 150W you're asking for. And that he cables should be 16 gauge for pigtails, but is typically 18 gauge which isn't as good.(Lower numbers are thinker wiring.) Also some could be using Aluminum wiring instead of copper which creates more heat. There is apparently enough variability in PSU specs and design that a daisy chain could work fine on PSU and be magic smoke on another. Is that alone a risk worth taking?
    If we do the math each PSU end power connection is 150W send and each GPU power connection is 150W request. So if we have a daisy chain on an EVGA FTW3 Ultra we have on the PSU the ability to send 150W x 2 + 75W from PCIE slot(375W total, 25W short of the 400W power draw at max load.) The GPU will be asking for potentially up to 3 X 150W +75W PCIE slot which is 525W total potential power requested. This is obviously not good if the PSU is trying to deliver more power than the connectors and cables are capable of handling. You'll only get that demand during peaks, but it only takes one 500W plus peak to make magic smoke.
     
    When you ask for more power that means more current(amps) and voltage. Wattage is literally volts multiplied by amps (W==v*a). Voltage can be modeled as the "amount" of electricity and current modeled as the "pressure of flow" in a sense. Current is more dangerous as a lot of electricity without "flow pressure" moving it doesn't do much except maybe look cool and tickle a little. You give a little voltage a 1 amp of current and that can kill people in contrast. When your GPU asks for power it's that extra current it's not rated to handle that will create the magic smoke.
    If we ask for more than the cable and/or connection can handle we have risk of "magic smoke." The PSU and GPU assume the cables can handle what they want to do. If the cable isn't good enough we get magic smoke at worst case. With a Daisy Chain we are asking for potentially 300W through a cable not at the correct gauge to handle that through a single 150W rated connection at the PSU. Also how does the PSU and GPU know to not push too much power through the Daisy chain cable? It doesn't know it's a daisy chain, it sees three 8 pin power connections and that it's getting power from them. How could it know not to push more than 150W through the daisy chain? (It doesn't, it could easily overload the daisy chain on the assumption that it's a properly rated cable.)
    It makes 0 logical or rational sense to use a daisy chain for 2000 or 3000 series. 3000 series is definitely drawing too much power for it to be smart to use a daisy chain. 2000 series seems to be borderlining it depending on specific GPU and PSU.
     
    1000 series had low enough power draw it was permissible. But even then I would not recommend it to be on the safer side. Jayz 2 Cents found his OC and performance was slightly limited on a 1080 something using a daisy chain. His results have not been verified by others repeating the same test, so scientifically it's not exactly solid data(yet.)
    Now add in that it kinda depends on your PSU and how well it followed specs like 16 gauge wiring for a daisy chain cable and copper wiring it seems like it's just not worth the risk to use a daisy chain at all, ever.
    I've come to question their existence. And now think they should not have ever been made. Daisy chains seem like a recipe for user error to destroy components. When it comes to making and selling a product an uniformed consumer could easily destroy it's prudent to minimize giving them ways to enact disastrous failure. Especially when there's a fire hazard potential.
    The rule of thumb should be this: One cable per 8 pin GPU connection. If they're 2 x 6 pin that's actually fine as 6 pin is only 75W and a daisy chain on 2 x 6 pin is 150W(2*75W.) But for newer builders than can be a point of confusion so we should really stick to a "One cable per 8 pin connector" mantra when it comes to GPU power.
     
    Thanks for coming to my Flange Talk. ;)

    "Humans are not rational animals, humans are rationalizing animals." -Robert A Heinlein
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    Intoxicus
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 09:05:39 (permalink)
    kougar
    The poster in question showed a photo of their PSU, and it was clear the PSU was designed with no less than FOUR outputs for PCIe cables. If the PSU is designed to split the load across multiple cables then it's always best to do so. Yes there are standards, but in the real world connectors do not always have good contact, whether that is due to oxidation or because the physical pins no longer perfectly match up.
     
    Case in point, I once had a 980X slag an EPS12v connector. It wasn't caused by extreme load, but by poor pin contact that increased the natural resistance until the connector began to scorch. It's always best to divide the load across multiple cables when at all possible just in case, because connectors do wear out over time and with use. When dealing with high-power electronics like a 3090 there's no sense not taking every precaution ahead of time to prevent issues later.   

     
    If we get into Buildzoid's video on the topic he talks about how the daisy chain cables are typically at 18 gauge when they should be 16 gauge. And also other potential discrepancies between recommended PSU specs and actual products in the wild.

    Also if the PSU is supplying 150W from the PSU side connection and the daisy is demanding 2X150W how do you think that will play out?
    (hint: it involves magic smoke at the worst case)

    Hoggle
    It’s always best to use separate cables but a standard does exist. It should be perfectly safe with a quality PSU so while I can see stability issues for an overclock it should be ok at stock.


    The PSU manufacturers and designers have to follow the non mandatory spec first. It seems you can not trust them to always be up to recommended specs. For example as previously stated it seems that too often the daisy chain cables are under spec and using the wrong gauge wiring. Which can create magic smoke it the cable is being asked to carry more power than it's capable of.
    post edited by Intoxicus - 2020/12/04 09:11:48

    "Humans are not rational animals, humans are rationalizing animals." -Robert A Heinlein
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    KingEngineRevUp
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 10:09:13 (permalink)
    Can I have a reference to this post on reddit you speak of? The daisy chain exist because it can be used as the 3rd plug, unless if you're going to XOC OC with a 550W+ bios or shunt mod. So they have their purpose. 
    post edited by KingEngineRevUp - 2020/12/04 10:11:55
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 10:19:40 (permalink)
    Intoxicus
    So doing some research it seems the 225W rating for the cables might be a misunderstanding. 
    It seems people are getting that from the 150W connector limit added to the 75W from PCI-E.
    Which if that is the case means you're only getting 150W from an 8 pin PCI-E cable. Not 225W.

    Which means at 150+150+75 you're 25W short of the 400W power limit using a splitter power cable on a 3 X 8 Pin 3080.

    The splitter may be rated for 150W at the connections sure. But can the cable itself handle that?

    Even if the cable could support 225W why push the limits on power connections and cables? It seems like an unnecessary risk for 0 benefit.






    A daisy chain cable is rated for 288W.
     
    PCI-E Slot = 75W
     
    Dedicated 8-pin = 150W
     
    Daisy Chain 8-Pin = 288W
     
    If you add all that up together that is 513W, so it's fine for a FTW3.
     
    See Seasonics diagram and see Jacob doing it too with his FTW3. 
     

     
    Seasonic diagram 
     

    post edited by KingEngineRevUp - 2020/12/04 10:22:22

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    Intoxicus
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 11:06:38 (permalink)
    KingEngineRevUp
    Intoxicus
    So doing some research it seems the 225W rating for the cables might be a misunderstanding. 
    It seems people are getting that from the 150W connector limit added to the 75W from PCI-E.
    Which if that is the case means you're only getting 150W from an 8 pin PCI-E cable. Not 225W.

    Which means at 150+150+75 you're 25W short of the 400W power limit using a splitter power cable on a 3 X 8 Pin 3080.

    The splitter may be rated for 150W at the connections sure. But can the cable itself handle that?

    Even if the cable could support 225W why push the limits on power connections and cables? It seems like an unnecessary risk for 0 benefit.






    A daisy chain cable is rated for 288W.
     
    PCI-E Slot = 75W
     
    Dedicated 8-pin = 150W
     
    Daisy Chain 8-Pin = 288W
     
    If you add all that up together that is 513W, so it's fine for a FTW3.
     
    See Seasonics diagram and see Jacob doing it too with his FTW3. 
     

     
    Seasonic diagram 
     




    I'm aware of those recommendations.
    I'm saying they're wrong. The whole point of my thread, etc is to point out that it seems they should not be making such recommendations.

    Do you have a valid reference that shows the cable itself is rated for 288W? The *connectors* are still only rated at 150W per connector even if the cable is rated for 288W.
    What is your source for that? Links please.

    Some people have been saying they're rated for 225W on forums and it seems that comes from adding the PCI-E slot to the 8pin connector rating. You'll need to provide a valid source for that 288W before I believe it.

    The daisy chain cables do have a purpose. For 2x6pin connectors on a GPU. Beyond that they should not be used. And when it comes to new builders it is safer to tell them "one cable per GPU power connection" so they don't get mixed up between 6 pin and 8 pin.

    Also you didn't show everything showing that tweet:

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    KingEngineRevUp
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 11:57:50 (permalink)


    I'm aware of those recommendations.
    I'm saying they're wrong. The whole point of my thread, etc is to point out that it seems they should not be making such recommendations.

    Do you have a valid reference that shows the cable itself is rated for 288W? The *connectors* are still only rated at 150W per connector even if the cable is rated for 288W.
    What is your source for that? Links please.

    Some people have been saying they're rated for 225W on forums and it seems that comes from adding the PCI-E slot to the 8pin connector rating. You'll need to provide a valid source for that 288W before I believe it.

    The daisy chain cables do have a purpose. For 2x6pin connectors on a GPU. Beyond that they should not be used. And when it comes to new builders it is safer to tell them "one cable per GPU power connection" so they don't get mixed up between 6 pin and 8 pin.

    Also you didn't show everything showing that tweet:





    When I have time, I will look up the standard for the daisy chained PCI-E cable. But people have been running shunt modded cards drawing 500-600W off of 2x 8-pins for the 20 and 30 series cards over at Overclock.net. You might ask, how are they doing that? And how have they been okay for a few years now? The answer has to do more with the quality of your PSU and cables. There are also other issues like bad contact, you can use 3 dedicated PCI-E cables and if there is bad contact with one of the connectors it can still fry the connector. Using 3 dedicated just lowers that probability since you're splitting power delivery between all the cables. 
     
    Der8auer made a good video about actually testing power cables checking voltages, current, power and temperature of the connectors and cables. 
     

     
    @16:50 "As a conclusion, there is no difference between running 2x 8-pin or 3x 8-pin and if you're having a discussion with your friends, please link them to this video."

    Again, he's using a good PSU and good cables. Obviously if you're using a **** budget PSU with crappy cables, you're playing with fire. 

    post edited by KingEngineRevUp - 2020/12/04 12:12:41
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    Delirious
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 12:16:08 (permalink)
    Post approved, sorry for the delay

    "Be quick to listen, slow to speak and slow to anger" 
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    Intoxicus
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 12:24:11 (permalink)
    Delirious
    Post approved, sorry for the delay


    All good and no worries :)

    Btw I love your quote in your sig! :D
    "education may be expensive but wait until you get the bill for ignorance" seems to be applicable to the topic of this thread ;)

    "Humans are not rational animals, humans are rationalizing animals." -Robert A Heinlein
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    KingEngineRevUp
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 13:04:31 (permalink)
    Intoxicus
    Delirious
    Post approved, sorry for the delay


    All good and no worries :)

    Btw I love your quote in your sig! :D
    "education may be expensive but wait until you get the bill for ignorance" seems to be applicable to the topic of this thread ;)




    So did you watch the Der8auer video or not? Because it would clear up a lot of "ignorance" on your part. 
     
     
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    Intoxicus
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 14:11:45 (permalink)
    KingEngineRevUp
    Intoxicus
    Delirious
    Post approved, sorry for the delay


    All good and no worries :)

    Btw I love your quote in your sig! :D
    "education may be expensive but wait until you get the bill for ignorance" seems to be applicable to the topic of this thread ;)




    So did you watch the Der8auer video or not? Because it would clear up a lot of "ignorance" on your part. 
     
     




    I'm subbed with notifications but sometimes one or two good ones slip by me.
    Edit 1:Oops, didn't notice you already had dropped a link, lol.
    Edit 2: I have watched it and it seemed not that useful or relevant to this topic. I will watch again anyway though.

    Right away being reminded of his Seasonic sponsorship makes me cautious. 
    Seasonic is the one with the image of bad advice people are trying to post to "counter" my conjectures and conclusions.

    Maybe there is not a conflict of interest, but I can't help but take whatever he says with a grain of salt because of the Seasonic sponsorship/ad.

    Also as always:
    Just because something can be shown to work in a specific test/experiment/circumstance doesn't mean you should do it or that it's ideal/safe/optimal for normal usage.

    One of the reason I say one connection per cable is because of the variability in power supplies following specs.
    Maybe it works with a Seasonic PSU and no other PSU?
    post edited by Intoxicus - 2020/12/04 14:19:01

    "Humans are not rational animals, humans are rationalizing animals." -Robert A Heinlein
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    KingEngineRevUp
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 14:19:40 (permalink)
    Intoxicus
    KingEngineRevUp
    Intoxicus
    Delirious
    Post approved, sorry for the delay


    All good and no worries :)

    Btw I love your quote in your sig! :D
    "education may be expensive but wait until you get the bill for ignorance" seems to be applicable to the topic of this thread ;)




    So did you watch the Der8auer video or not? Because it would clear up a lot of "ignorance" on your part. 
     
     




    I'm subbed with notifications but sometimes one or two good ones slip by me.
    Oops, didn't notice you already had dropped a link, lol.

    Right away being reminded of his Seasonic sponsorship makes me cautious. 
    Seasonic is the one with the image of bad advice people are trying to post to "counter" my conjectures and conclusions.

    Maybe there is not a conflict of interest, but I can't help but take whatever he says with a grain of salt because of the Seasonic sponsorship/ad.

    Also as always:
    Just because something can be shown to work in a specific test/experiment/circumstance doesn't mean you should do it or that it's ideal/safe/optimal for normal usage.

    One of the reason I say one connection per cable is because of the variability in power supplies following specs.
    Maybe it works with a Seasonic PSU and no other PSU?




    But his test have nothing to do with his seasonic sponsership. He literally continues to cut wires, measures voltage drops, measures amperage, measure temperature of the cable. Essentially he gets down to drawing 175W of power into only 4 cables, two of them grounded I believe. So power is split between two cables in the end. The voltage drop doesn't change. The cable temperature is also okay, it's within spec which is written write on the cable that he reads off. 
     
    It's a very scientific approach where he does this with several measuring tools and does it live with furmark running in the background. 
     
     
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    Intoxicus
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 14:25:53 (permalink)
    Some additional info:

    Intel makes the PSU specifications and if you search ATX design guide you can find some useful .pdf files that don't seem to say a thing about daisy chain PCI-E power cables. As far as I can tell they're not even in the Intel ATX specifications.

    The connectors are Molex Mini Fit Jr 5556. They are rated at 13a @ 12v giving us 156W (not 150W, lol.)
    Even if a cable can support more than 156W the connector will bottleneck that.

    I'm still hoping an actual Electrical Engineer will notice this and weigh in...

    I've talked to a friend that isn't an Electrical Engineer but has training, education, and experience close enough. He agrees without question that using both connectors on a Daisy Chain is a bad idea. 
    What is most interesting to me on this topic is people with the education and experience to have a fact based critique of my OP with data and references I can look at. As in an Electrical Engineer or equivalent.

    Nothing I can find tells me it's a good idea to use a daisy chain on anything more than a 2x6 pin GPU.

    And when it comes to new builders it seems the safest and easiest to tell them "one connection per GPU power cable."

    "Humans are not rational animals, humans are rationalizing animals." -Robert A Heinlein
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    Intoxicus
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 14:28:29 (permalink)
    KingEngineRevUp
    Intoxicus
    KingEngineRevUp
    Intoxicus
    Delirious
    Post approved, sorry for the delay


    All good and no worries :)

    Btw I love your quote in your sig! :D
    "education may be expensive but wait until you get the bill for ignorance" seems to be applicable to the topic of this thread ;)




    So did you watch the Der8auer video or not? Because it would clear up a lot of "ignorance" on your part. 
     
     




    I'm subbed with notifications but sometimes one or two good ones slip by me.
    Oops, didn't notice you already had dropped a link, lol.

    Right away being reminded of his Seasonic sponsorship makes me cautious. 
    Seasonic is the one with the image of bad advice people are trying to post to "counter" my conjectures and conclusions.

    Maybe there is not a conflict of interest, but I can't help but take whatever he says with a grain of salt because of the Seasonic sponsorship/ad.

    Also as always:
    Just because something can be shown to work in a specific test/experiment/circumstance doesn't mean you should do it or that it's ideal/safe/optimal for normal usage.

    One of the reason I say one connection per cable is because of the variability in power supplies following specs.
    Maybe it works with a Seasonic PSU and no other PSU?




    But his test have nothing to do with his seasonic sponsership. He literally continues to cut wires, measures voltage drops, measures amperage, measure temperature of the cable. Essentially he gets down to drawing 175W of power into only 4 cables, two of them grounded I believe. So power is split between two cables in the end. The voltage drop doesn't change. The cable temperature is also okay, it's within spec which is written write on the cable that he reads off. 
     
    It's a very scientific approach where he does this with several measuring tools and does it live with furmark running in the background. 
     
     



    A conflict of interest can be such that the person knows if they upset their patron by speaking too negatively or in a way they don't like they lose said patronage.

    It doesn't have to be direct, it can be the back of the mind pressure of "don't piss off Seasonic too much so they keep giving me money to run their ads."

    I have all respect for Debauer. We are all human though and subject to the faults of being human.

    Again I don't know. I'm only saying it makes me want to extra double fact check him to be sure.

    "Humans are not rational animals, humans are rationalizing animals." -Robert A Heinlein
    #17
    Intoxicus
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 14:35:51 (permalink)
    KingEngineRevUp
    Intoxicus
    KingEngineRevUp
    Intoxicus
    Delirious
    Post approved, sorry for the delay


    All good and no worries :)

    Btw I love your quote in your sig! :D
    "education may be expensive but wait until you get the bill for ignorance" seems to be applicable to the topic of this thread ;)




    So did you watch the Der8auer video or not? Because it would clear up a lot of "ignorance" on your part. 
     
     




    I'm subbed with notifications but sometimes one or two good ones slip by me.
    Oops, didn't notice you already had dropped a link, lol.

    Right away being reminded of his Seasonic sponsorship makes me cautious. 
    Seasonic is the one with the image of bad advice people are trying to post to "counter" my conjectures and conclusions.

    Maybe there is not a conflict of interest, but I can't help but take whatever he says with a grain of salt because of the Seasonic sponsorship/ad.

    Also as always:
    Just because something can be shown to work in a specific test/experiment/circumstance doesn't mean you should do it or that it's ideal/safe/optimal for normal usage.

    One of the reason I say one connection per cable is because of the variability in power supplies following specs.
    Maybe it works with a Seasonic PSU and no other PSU?




    But his test have nothing to do with his seasonic sponsership. He literally continues to cut wires, measures voltage drops, measures amperage, measure temperature of the cable. Essentially he gets down to drawing 175W of power into only 4 cables, two of them grounded I believe. So power is split between two cables in the end. The voltage drop doesn't change. The cable temperature is also okay, it's within spec which is written write on the cable that he reads off. 
     
    It's a very scientific approach where he does this with several measuring tools and does it live with furmark running in the background. 
     
     


     - He opens up talking about 2080 Ti cards in a context not really relevant to this topic. Indirectly, sure, but not directly.
    - "But that's the point. PSUs these days are no longer following the specs" - Debauer @ about 1:25

    Firstly what he's getting at is if you need a 3rd PCI-E connector to get better OC on a 2080 Ti. This is why I didn't put much stock in this video when it comes to the specific topic at hand.

    With 2 minutes he says something I've also been saying is the reason to not use daisy chains...

    "Humans are not rational animals, humans are rationalizing animals." -Robert A Heinlein
    #18
    KingEngineRevUp
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 14:41:29 (permalink)
    Intoxicus
    Some additional info:

    Intel makes the PSU specifications and if you search ATX design guide you can find some useful .pdf files that don't seem to say a thing about daisy chain PCI-E power cables. As far as I can tell they're not even in the Intel ATX specifications.

    The connectors are Molex Mini Fit Jr 5556. They are rated at 13a @ 12v giving us 156W (not 150W, lol.)
    Even if a cable can support more than 156W the connector will bottleneck that.

    I'm still hoping an actual Electrical Engineer will notice this and weigh in...

    I've talked to a friend that isn't an Electrical Engineer but has training, education, and experience close enough. He agrees without question that using both connectors on a Daisy Chain is a bad idea. 
    What is most interesting to me on this topic is people with the education and experience to have a fact based critique of my OP with data and references I can look at. As in an Electrical Engineer or equivalent.

    Nothing I can find tells me it's a good idea to use a daisy chain on anything more than a 2x6 pin GPU.

    And when it comes to new builders it seems the safest and easiest to tell them "one connection per GPU power cable."


    I am aware of that PDF and have a copy for myself.

    I'm not a EE, but the first job as an ME I had was designing EVSE and EVSE power delivery wire harnesses. You have to keep in mind there's a "factor of safety" built in to everything.

    If a PSU bundled a daisy chain, there has to be a safe way to use it, it doesn't make sense they would risk lawsuits over it. Things are also over engineered for reasons like this, specially at consumer level because again, a good Engineer has to take into account their user base.

    EDIT: Look at extension cables and how much power the 16 AWG cables have to carry
     

    The cable itself in a PC is usually 18 or 16 AWG. Like another user said, it's not the cable that usually is the point of failure, it's the contact ends. The cable themselves have a lot of headroom in terms of how much power can go through them. The contacts, not so much. Bad contact can cause the failure. 
     
    A daisy chain would split the power and therefore the contacts would be delivering and receiving what they would in a dedicated scenario. I don't see any reason why 1 dedicated and 1 daisy chain can't run the FTW3. I haven't had any issues with my FTW3 running it in the same configuration EVGA Jacob is. 
     

     
    So really, the issue is more than likely:
     
    1. A poor quality power supply
    2. Using sleeved extension cables that ruin the spec of the whole wire harness
    3. Using custom cables that don't have built in capacitors to clean up the cable noise
    4. Contacts that have gone bad
     
    My point to you is, whatever caused that card to fail on reddit, it's possible the same failure can happen with 3x dedicated if the PSU sucks or the contact is bad (oxidation, deformed pins from constant installs and fatigue, etc)
     
    Again, Der8auer did a test making the cables themselves draw more and more power and they still ran within spec. 
    post edited by KingEngineRevUp - 2020/12/04 14:54:02

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    aardvark1134
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 14:43:12 (permalink)
    2 things
    1)   The main reason for dual cables were so you can use 2x6pin or 1x6 and 1x8 off a single cord.
    I would not use 2x8 off the same cord even though it is possible to do.
    2)   Everyone who supports using both x8s off 1 cord seems to always quote the exact same picture from one of the very best brands of power supplies...that in no way shape or form means that every brand especially a low end model of a cheap brand can handel that just because one of the top 3 brands can.   
    Last whenever you are pushing some to the max it's suppost to support you greatly increase the chance of issues...which is why in a house you are only supposed to pull 80% of max from a circuit if drawing for more than a couple min and even less if you may pull that much for hrs straight.

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    Intoxicus
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 14:56:36 (permalink)
    KingEngineRevUp
    Intoxicus
    Some additional info:

    Intel makes the PSU specifications and if you search ATX design guide you can find some useful .pdf files that don't seem to say a thing about daisy chain PCI-E power cables. As far as I can tell they're not even in the Intel ATX specifications.

    The connectors are Molex Mini Fit Jr 5556. They are rated at 13a @ 12v giving us 156W (not 150W, lol.)
    Even if a cable can support more than 156W the connector will bottleneck that.

    I'm still hoping an actual Electrical Engineer will notice this and weigh in...

    I've talked to a friend that isn't an Electrical Engineer but has training, education, and experience close enough. He agrees without question that using both connectors on a Daisy Chain is a bad idea. 
    What is most interesting to me on this topic is people with the education and experience to have a fact based critique of my OP with data and references I can look at. As in an Electrical Engineer or equivalent.

    Nothing I can find tells me it's a good idea to use a daisy chain on anything more than a 2x6 pin GPU.

    And when it comes to new builders it seems the safest and easiest to tell them "one connection per GPU power cable."


    I am aware of that PDF and have a copy for myself.

    I'm not a EE, but the first job as an ME I had was designing EVSE and EVSE power delivery wire harnesses. You have to keep in mind there's a "factor of safety" built in to everything.

    If a PSU bundled a daisy chain, there has to be a safe way to use it, it doesn't make sense they would risk lawsuits over it. Things are also over engineered for reasons like this, specially at consumer level because again, a good Engineer has to take into account their user base.

    EDIT: Look at extension cables and how much power the 16 AWG cables have to carry
     

    The cable itself in a PC is usually 18 or 16 AWG. Like another user said, it's not the cable that usually is the point of failure, it's the contact ends. The cable themselves have a lot of headroom in terms of how much power can go through them. The contacts, not so much. Bad contact can cause the failure. 
     
    A daisy chain would split the power and therefore the contacts would be delivering and receiving what they would in a dedicated scenario. 
     

     
    So really, the issue is more than likely:
     
    1. A poor quality power supply
    2. Using sleeved extension cables that ruin the spec of the whole wire harness
    3. Using custom cables that don't have built in capacitors to clean up the cable noise
    4. Contacts that have gone bad
     
    My point to you is, whatever caused that card to fail on reddit, it's possible the same failure can happen with 3x dedicated if the PSU sucks or the contact is bad (oxidation, deformed pins from constant installs and fatigue, etc)
     
    Again, Der8auer did a test making the cables themselves draw more and more power and they still ran within spec. 



    I think you're missing a big massive point:

    **If they're not following the specs can you trust a daisy chain cable when you don't know how close to spec it is or is not and in which direction.**

    If you want to take the risk it's your GPU, your potential for magic smoke, etc

    What I'm trying to say is *don't tell others, especially new builders, to do things that are risky."

    If you want to take the risk that is your choice as long as no one else gets harmed by it.

    Don't put that risk on others when we can't even say for sure what wattage the cables are actually rated for and we have a reliable source saying they're not even the correct gauge most of the time.

    Also maybe Seasonic knows their design can handle it. *If so then what they instruct for their PSUs only applies to Seasonic PSU and can not be given as general advice for all PSUs.*

    Again sometimes just because you can does not mean you should.
    Or tell others to do so.

    Because Debauer can show something in a specific experimental context intended to prove/disprove something tangentially related does not mean it's a good idea for everyday general use.

    "Humans are not rational animals, humans are rationalizing animals." -Robert A Heinlein
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    KingEngineRevUp
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 15:08:51 (permalink)


    I think you're missing a big massive point:

    **If they're not following the specs can you trust a daisy chain cable when you don't know how close to spec it is or is not and in which direction.**

    If you want to take the risk it's your GPU, your potential for magic smoke, etc

    What I'm trying to say is *don't tell others, especially new builders, to do things that are risky."

    If you want to take the risk that is your choice as long as no one else gets harmed by it.

    Don't put that risk on others when we can't even say for sure what wattage the cables are actually rated for and we have a reliable source saying they're not even the correct gauge most of the time.

    Also maybe Seasonic knows their design can handle it. *If so then what they instruct for their PSUs only applies to Seasonic PSU and can not be given as general advice for all PSUs.*

    Again sometimes just because you can does not mean you should.
    Or tell others to do so.

    Because Debauer can show something in a specific experimental context intended to prove/disprove something tangentially related does not mean it's a good idea for everyday general use.




    Okay, well I have NOT seen you do anything to prove Seasonic and De8auer wrong or shown any scientific approaches. The only counter argument you have made so far is a conspiracy theory. He didn't make his video to defend seasonic either, it was mostly due to him doing shunt modes and people asking him if it's safe or will his cables light on fire. That was the point of his video. It had nothing to do with seasonic. The image I posted was coincidental. 
     
    #22
    rain2_usa
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 15:09:54 (permalink)
    I see all of these arguments about not using both connectors in a daisy chain invalid.  There's no reason to have a daisy chain connector capable of having 2 - 8pin connectors if it wasn't meant to be used at the same time.  If there was an issue, there would be a warning label NOT to use it under certain circumstances; not buried on a website somewhere.  There would/should be a cap/sticker on one of the connectors or similar stating as such.  
    And also remember the days of the 4pin molex.  I know I daisy chained the heck out of those in the 486/Pentium days.  CD, 5-1/4" floppy, 3-1/2" floppy, tape drive, zip drive, Master and Slave hard drives, Fans, etc.  As long as you had the proper wattage PSU, it was all good.  
    My 2 cents.

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    #23
    Intoxicus
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 16:13:25 (permalink)
    KingEngineRevUp


    I think you're missing a big massive point:

    **If they're not following the specs can you trust a daisy chain cable when you don't know how close to spec it is or is not and in which direction.**

    If you want to take the risk it's your GPU, your potential for magic smoke, etc

    What I'm trying to say is *don't tell others, especially new builders, to do things that are risky."

    If you want to take the risk that is your choice as long as no one else gets harmed by it.

    Don't put that risk on others when we can't even say for sure what wattage the cables are actually rated for and we have a reliable source saying they're not even the correct gauge most of the time.

    Also maybe Seasonic knows their design can handle it. *If so then what they instruct for their PSUs only applies to Seasonic PSU and can not be given as general advice for all PSUs.*

    Again sometimes just because you can does not mean you should.
    Or tell others to do so.

    Because Debauer can show something in a specific experimental context intended to prove/disprove something tangentially related does not mean it's a good idea for everyday general use.




    Okay, well I have NOT seen you do anything to prove Seasonic and De8auer wrong or shown any scientific approaches. The only counter argument you have made so far is a conspiracy theory. He didn't make his video to defend seasonic either, it was mostly due to him doing shunt modes and people asking him if it's safe or will his cables light on fire. That was the point of his video. It had nothing to do with seasonic. The image I posted was coincidental. 
     


    That is not what I said, lol. Don't put words in my mouth like that.

    Taking things with a grain of salt and extra fact checking due to a potential conflict of interest is what rational and sane people should do. I never ever said there was any "conspiracy" or anything of thay nature.

    I said it gives me reason to extra fact check the video. I never said it made it invalid.

    Also I said it's not directly related as it's seeking to prove something else that is tangentially related. And uses 2080 Ti cards. Not 30 series cards.

    I also said because he can do that does not prove daisy chain cables are safe because a single specifically expiremental case can not necessarily be applied to daily general use.

    Also he did prove his point, that a 2080 TI doesn't need 3x 8 pin. Which is not what this topic is about....

    He does have a some valid points that are relevant you failed to mention.

    That extra pin in the 6 pin above spec can make a difference. *But you can not expect new builders to know to check for this!*

    And it's a bit ridiculous to expect the average consumer to do the research to know these details and nuances.

    We're talking about what should we tell new and inexperienced builders to do. Should EVGa and Seasonic be telling customers to use both daisy chain connectors. And if they do should they specific about it only applying to their products and specifying thay they can't comment on other brands products.

    People are using the Seasonic chart like it applies to all PSUs. Like I said perhaps Seasonic knows their products can handle it. *You can't apply that to every other brand of PSU though.*

    And to end it off a single experimental result is unscientific. Science requires repeatablility in results for data to be valid. Other people have to perform the exact same expiriment the exact same way and get the same results within margin of error for the results to be scientifically valid.

    Debauer's video is cool, valid, proves his point unscientifically, and is not scientific without repeatable results and recorded data.

    I respect Debauer and his content. He does good work and quality content, in two languages no less.

    He's still human, and flawed like all of us are. He's not perfect, and can be wrong with the best of intentions. "Because Debauer said so" or "Because Seasonic said so" is an Appeal to Authority fallacy.

    I'm asking for links to specifications directly related to the specific hardware in question.

    An infographic about AC wall power specs is not exactly relevant. Nor the kind of information I asked to be brought to the table. Neither is the Seasonic chart I've already seen that everyone and their cat has linked at me a dozen times.

    Link me some manufacturer's specifications and/or engineering specifications
    on stuff like Molex Mini Fit Jr 5556, PCI-E daisy chain cables, ATX power supplies, etc and we can resume our debate.

    So far the ATX PSU design guide from Intel says nothing about daisy chain cables I can find. As far as I can tell the cable specs derive from the Molex Mini Fit Jr 5556 Specs.

    "Humans are not rational animals, humans are rationalizing animals." -Robert A Heinlein
    #24
    KingEngineRevUp
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 16:20:45 (permalink)
    Okay, lets just go over specifications and math here. 
    1. Power (W) = Voltage (V) * Current (A) and we're on 12V rails so that's determined. V = 12V
    2. The cables used at a minimum I have seen are 18 AWG, the maximum amperage these are rated at for DC 12V is 8A for the average PCI-E cable length, around 0.5-0.65M long. I = 8A
    3. 8-Pin PCI-E cable has 3 pair of live and ground wires and one pair of sensors, so we have 3x line drawing power
    4. The pins used are rated for 18 AWG, obviously https://www.molex.com/webdocs/datasheets/pdf/en-us/0457501111_CRIMP_TERMINALS.pdf 

    So how much power can a PCI-E actually handle after factors of safeties are taken into account?
    1. P = 12V * 8A = 96W per a line
    2. 3 * 96W = 288W for the whole connector
    Next lets review two different types of PSU. Single rail vs multi rail: https://www.deskdecode.co...le-rail-vs-multi-rail/
    In case of single rail, the +12V power supply is monitored through one single circuit and there is just one OCP chip configured. The chip gets off as soon as the max amp is reached.
     
    But in case of multi-rail PSU, the +12V power source is monitored by multiple OCP chip configured on the PSU. There are more than two monitoring channels and all of them have separate amp rating. These amp ratings are the division of the total output of the PSU.
     
     
    Lets assume we're using a good single rail PSU here. It doesn't matter if you have 2 or 3 dedicated PCI-E 8-pins to draw out power, the power requested will be drawn on a single rail. So if a card is not designed, programmed and made to regulate power, it will just suck up as much power as it's calling for. 
     
    Lets go to the multi rail, if there is a rail limit per a connector, then the PSU will stop the device from drawing its amx power, in this case above a single rail can't go above 40A. Some crappier PSU have less. 
     
    So what happens when a 450W card like the FTW3 with XOC bios running is connected like the top right illustration? Lets assume each PCI-E connect asks for the same.
     

     
    1. (450W-75W) / 3 = 125W [The 75W that was deducted came from the PCI-E slot and motherboard]
    2. We have one dedicated PCI-E and one daisy chain
    3. The dedicated will have 125W pulled, that's fine
    4. The daisy chain will have 250W pulled, is that fine? According to the specs we worked with above, yes
    288W > 250W, we're in the clear And remember, this is after a factor of safety is accounted for. These cables can handle fluctuations. De8bauer already showed a video of him passing rated amperage draw and the temperatures stayed within spec. 
     
    And lets not forget, the FTW3 stock is actually limited to 420W, so that's 30W less than the calculations I did above. 
     
    Why do some people have issues then? That's a much deeper question to answer, but the setup above is not the issue. It is more than likely the PSU, a bad contact or something fabricated poorly or wrong. We're talking about unforeseen unlucky circumstances. 
     
    At the end of the day, if you're worried then consult your PSU manufacturer and ask them "why did you give me a daisy chain cable? Can I safely use it in this configuration?"
     
     
     
    post edited by KingEngineRevUp - 2020/12/04 16:56:31

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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 16:27:44 (permalink)
    Intoxicus
    KingEngineRevUp


    I think you're missing a big massive point:

    **If they're not following the specs can you trust a daisy chain cable when you don't know how close to spec it is or is not and in which direction.**

    If you want to take the risk it's your GPU, your potential for magic smoke, etc

    What I'm trying to say is *don't tell others, especially new builders, to do things that are risky."

    If you want to take the risk that is your choice as long as no one else gets harmed by it.

    Don't put that risk on others when we can't even say for sure what wattage the cables are actually rated for and we have a reliable source saying they're not even the correct gauge most of the time.

    Also maybe Seasonic knows their design can handle it. *If so then what they instruct for their PSUs only applies to Seasonic PSU and can not be given as general advice for all PSUs.*

    Again sometimes just because you can does not mean you should.
    Or tell others to do so.

    Because Debauer can show something in a specific experimental context intended to prove/disprove something tangentially related does not mean it's a good idea for everyday general use.




    Okay, well I have NOT seen you do anything to prove Seasonic and De8auer wrong or shown any scientific approaches. The only counter argument you have made so far is a conspiracy theory. He didn't make his video to defend seasonic either, it was mostly due to him doing shunt modes and people asking him if it's safe or will his cables light on fire. That was the point of his video. It had nothing to do with seasonic. The image I posted was coincidental. 
     


    That is not what I said, lol. Don't put words in my mouth like that.

    Taking things with a grain of salt and extra fact checking due to a potential conflict of interest is what rational and sane people should do. I never ever said there was any "conspiracy" or anything of thay nature.

    I said it gives me reason to extra fact check the video. I never said it made it invalid.

    Also I said it's not directly related as it's seeking to prove something else that is tangentially related. And uses 2080 Ti cards. Not 30 series cards.

    I also said because he can do that does not prove daisy chain cables are safe because a single specifically expiremental case can not necessarily be applied to daily general use.

    Also he did prove his point, that a 2080 TI doesn't need 3x 8 pin. Which is not what this topic is about....

    He does have a some valid points that are relevant you failed to mention.

    That extra pin in the 6 pin above spec can make a difference. *But you can not expect new builders to know to check for this!*

    And it's a bit ridiculous to expect the average consumer to do the research to know these details and nuances.

    We're talking about what should we tell new and inexperienced builders to do. Should EVGa and Seasonic be telling customers to use both daisy chain connectors. And if they do should they specific about it only applying to their products and specifying thay they can't comment on other brands products.

    People are using the Seasonic chart like it applies to all PSUs. Like I said perhaps Seasonic knows their products can handle it. *You can't apply that to every other brand of PSU though.*

    And to end it off a single experimental result is unscientific. Science requires repeatablility in results for data to be valid. Other people have to perform the exact same expiriment the exact same way and get the same results within margin of error for the results to be scientifically valid.

    Debauer's video is cool, valid, proves his point unscientifically, and is not scientific without repeatable results and recorded data.

    I respect Debauer and his content. He does good work and quality content, in two languages no less.

    He's still human, and flawed like all of us are. He's not perfect, and can be wrong with the best of intentions. "Because Debauer said so" or "Because Seasonic said so" is an Appeal to Authority fallacy.

    I'm asking for links to specifications directly related to the specific hardware in question.

    An infographic about AC wall power specs is not exactly relevant. Nor the kind of information I asked to be brought to the table. Neither is the Seasonic chart I've already seen that everyone and their cat has linked at me a dozen times.

    Link me some manufacturer's specifications and/or engineering specifications
    on stuff like Molex Mini Fit Jr 5556, PCI-E daisy chain cables, ATX power supplies, etc and we can resume our debate.

    So far the ATX PSU design guide from Intel says nothing about daisy chain cables I can find. As far as I can tell the cable specs derive from the Molex Mini Fit Jr 5556 Specs.



    I posted my final post on the matter above. I'm not going to bother discussing conspiracy theories. I'm going to go off of facts, specs, calculations and what I did when I worked with EEs to design electrical wire harnesses. I am a ME by trade and our curriculum has has take a few EE classes as well but a EE can chime in, feel free. 
     
    EDIT: The post I made is pending approval from the mod because of the amount of images I attached. Standby please. 
    post edited by KingEngineRevUp - 2020/12/04 16:34:10
    #26
    Delirious
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 16:51:20 (permalink)
    Post approved sorry for any delay

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    #27
    KingEngineRevUp
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 16:54:12 (permalink)
    Delirious
    Post approved sorry for any delay

    Thank you. 
    #28
    aardvark1134
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 17:04:35 (permalink)
    rain2_usa
    I see all of these arguments about not using both connectors in a daisy chain invalid.  There's no reason to have a daisy chain connector capable of having 2 - 8pin connectors if it wasn't meant to be used at the same time.  If there was an issue, there would be a warning label NOT to use it under certain circumstances; not buried on a website somewhere.  There would/should be a cap/sticker on one of the connectors or similar stating as such.  
    And also remember the days of the 4pin molex.  I know I daisy chained the heck out of those in the 486/Pentium days.  CD, 5-1/4" floppy, 3-1/2" floppy, tape drive, zip drive, Master and Slave hard drives, Fans, etc.  As long as you had the proper wattage PSU, it was all good.  
    My 2 cents.


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    #29
    ilkali
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    Re: GPU Power: One cable, One connection; no splitter cables. 2020/12/04 17:11:24 (permalink)
    Intoxicus

    The connectors are Molex Mini Fit Jr 5556. They are rated at 13a @ 12v giving us 156W (not 150W, lol.)
    Even if a cable can support more than 156W the connector will bottleneck that.





    I believe you're wrong here. This specification is 13A per circuit, not whole connector. 13A is the max limit, 11A is more realistic as I think it is the HCS standars, which gives 12*3*11 = 396 W of power per connector safely. 
     
    This number is the molex specification and it should be obeyed as going over that is dangerous. 150W limit of the PCIe specification is a more arbitrary number to ensure a wide array of compatibility. Anyway, with the FE cards, nvidia is bypassing the PCIe specification but they still have to abide by molex standards. 
     
    Also main reason that the 3080 and 3090's shouldnt be daisy chained is not their sustained power consumption but their power spikes. It's been shown that 3080s can have momentary power spikes of 489 Watts while 3090's can reach as high as 573 Watt, which is well above the molex specifications and is dangerous to daisy chain. But for a 3060 TI, which is just pulling 200 watts normally while reaching 340-350 momentary peaks, it's not the end of the world to use a daisy chained cable as you're still within the specs.
     
     
    #30
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