Question on GPU rig build

[Bob-Bit]

Hello. Was wondering something, perhaps someone can answer my question. So, on Nvidia 1070 cards I've seen, there is a plug with 6 pins and one with 8 pins. The plugs from a nice modular power supply (Corsair or EVGA) have an 8 pin and a 6 pin branched off on the end of the cable. Can just one cable power one 1070 using the 8, and 6 pin connector from one modular cable? Or does each card have to eat up 2 of the modular plugs on the power supply side (and use 2 seperate cables)? Thank you for the help, I appreciate it!

[dealpass]

I only have AMD RX gpus, and they use the 8 pin plug for the GPU. You should be fine with one modular plug per card. I could technically plug in two cards on each of my plugs... however, I have read that that is not recommended so I have not tried it. Then you connect the sata power plugs to the PCIE powered risers.

[leonix007]

Or does each card have to eat up 2 of the modular plugs on the power supply side (and use 2 seperate cables)? Thank you for the help, I appreciate it!

A one PCIe cable with 8 and 6 pin connector will do, more important is to understand  how much power each cable could handle which corresponds to your GPU.

this is a good reference for PSU cables.

http://www.gpuminingresources.com/p/psu-cables.html

[remauto1187ma]

I only have AMD RX gpus, and they use the 8 pin plug for the GPU. You should be fine with one modular plug per card. I could technically plug in two cards on each of my plugs... however, I have read that that is not recommended so I have not tried it. Then you connect the sata power plugs to the PCIE powered risers.

You understand nothing about electricity or circuits and how they work.


There is a reason why some cards have an 8 pin and a 6 pin socket. The 6 pin just supplies 3/4 more power on top of the 8 pin and is used for more power hungry cards such as the 1080.  First lets get it all straightened out as to what all those wires are for.  The top row are all 12vd+ wires that are all COMMON to each other.  The bottom row is DC Ground. Or in other words the negative of the 12v power supply rail.   Having each wire positive or negative goto its own pin that ultimately is soldered to the circuit board keeps all the current split up and going into the circuit board instead of ALL of the current going thru one or two or even just 8 pins.  They are only rated for so much current flow.  Exceed that rating and things get hot and melt. 10 amps going thru 7 pins (7 is half of 14, remember one half is pos and the other neg) instead of just 4 reduces the current flow in each pin of the socket.  This also reduces the flow in each of the feed wires that lead from the plug in the power supply going into your PCIE power wires by splitting up the wires into multiple pos and neg wires.

[JaredKaragen]

I only have AMD RX gpus, and they use the 8 pin plug for the GPU. You should be fine with one modular plug per card. I could technically plug in two cards on each of my plugs... however, I have read that that is not recommended so I have not tried it. Then you connect the sata power plugs to the PCIE powered risers.

You understand nothing about electricity or circuits and how they work.


There is a reason why some cards have an 8 pin and a 6 pin socket. The 6 pin just supplies 3/4 more power on top of the 8 pin and is used for more power hungry cards such as the 1080.  First lets get it all straightened out as to what all those wires are for.  The top row are all 12vd+ wires that are all COMMON to each other.  The bottom row is DC Ground. Or in other words the negative of the 12v power supply rail.   Having each wire positive or negative goto its own pin that ultimately is soldered to the circuit board keeps all the current split up and going into the circuit board instead of ALL of the current going thru one or two or even just 8 pins.  They are only rated for so much current flow.  Exceed that rating and things get hot and melt. 10 amps going thru 7 pins (7 is half of 14, remember one half is pos and the other neg) instead of just 4 reduces the current flow in each pin of the socket.  This also reduces the flow in each of the feed wires that lead from the plug in the power supply going into your PCIE power wires by splitting up the wires into multiple pos and neg wires.

to add some clarity;

The 8 pin connector doesn't add one more + and - line, but it only in fact adds two more grounds only.

Liken the need for 2 more grounds to having a fire hose;  and you wanted to increase the pressure on the inlet.... so you want to beef up the inlet, whereas the outlet won't feel the stress the inlet does.   Since electricity flows in a magical circle from negative to positive;  you need to beef up the negative coupling.  This isn't 100% correct;  but good enough for the layman to understand.


I may have analogized that kind of wrong;  but its pretty close to a good description on reasoning.



In short;  if you are running a GPU off one cable;  as long as the AWG of that cable can support the card's wattage (factoring in the PCIE 16x port's power draw), you can use both connectors on the one pcie cable to power the GPU.

[[YAZ]]

Referring to leonix007 post, 8 pins from PSU that split to whatever (8 and 8 / 8 and 6) would produce max 150 Watt (combined). Let's assume that you are using a powered riser and using MOLEX or 6 Pins power that will produce max 75 Watt. So you have max power 150+75=225 Watt.
If you do safe calculations, you could use TDP. NVIDIA 1080 TDP is 180 Watt, so you still safe on it, even when you are using SATA power (150+54=204 Watt)

But, you could see this:

[Bob-Bit]

Great, the MSI 1070 card I'm looking at is 150w apiece so they'll be fine with one cable each, and with one of those 1600w Corsair power supplies with 10 vga ports I can use 8 of them for those cards and call it George. Sweet.

[remauto1187ma]

Great, the MSI 1070 card I'm looking at is 150w apiece so they'll be fine with one cable each, and with one of those 1600w Corsair power supplies with 10 vga ports I can use 8 of them for those cards and call it George. Sweet.

If it has one 8 pin and one 6pin on the GPU, the extra is there for a reason!  To keep the common point for the 12vdc+ and the common point for the 12vdc- on the circuit board from flowing too much current thru the pins that are soldered to the circuit board.  Exceed the rating and it all melts at the circuit board.  But you go ahead and take the short cut over q $5 cable and see what happens.

[Bob-Bit]

I don't think it's a short cut from what I'm understanding. What we all just discussed was that each cable (the one with an 8 pin and 6 pin connectors branched off) can do 150w total, and the riser does 75w for a total of 225w. So that's well within the range of powering a 150w 1070 video card. It has nothing to do with not wanting to buy an extra cable, the problem is if I used 2 ports on the power supply for each card I could only power 4 or 5 cards from one 1500 or 1600 watt power supply. What am I going to do, use 3 power supplies for a 12 card rig? That would be.....inconvenient.

[[YAZ]]

what we suggest here is a safer calculation. 204-205 Watt still enough for your card (if you decide to use single cable 8 pins), or else you can buy Molex to 6 pins for powering 6 pins socket on your cards.

[Bob-Bit]

I get safety, but as I mentioned, the MSI 1070 card I'm looking at uses 150w, the one in your table uses 307.

[JaredKaragen]

I get safety, but as I mentioned, the MSI 1070 card I'm looking at uses 150w, the one in your table uses 307.

... say it uses 150w mining 'n' algo with 'x' settings....  it varies depending.

Algos like skien take a LOT less power than lets say NIST5.   This is one of the reasons last year and the year before skien was soo damned profitable.  Not many people saw it that way.

When you calculate your rig's power requirements; you must be sure that the rig can not exceed those requirements due to a misconfiguration, new algo, etc.  If you build for what the card is capable of, you have one major issue that can't creep up on you.

We had machines that were running the edge of what they could provide power for.   Worked fine for ~ a year.   Then;  all sorts of strange problems started happening;  and still happen.  Adding a second power supply helped immensely, but it still has random GPU dropouts and odd issues every once in a while.

[remauto1187ma]

I don't think it's a short cut from what I'm understanding. What we all just discussed was that each cable (the one with an 8 pin and 6 pin connectors branched off) can do 150w total, and the riser does 75w for a total of 225w. So that's well within the range of powering a 150w 1070 video card. It has nothing to do with not wanting to buy an extra cable, the problem is if I used 2 ports on the power supply for each card I could only power 4 or 5 cards from one 1500 or 1600 watt power supply. What am I going to do, use 3 power supplies for a 12 card rig? That would be.....inconvenient.

You are confusing the safe rating of the power cable with what im referring to at the socket on the GPU.  Sure the power cable can handle it.  The problem is trying to run all the power thru the 8pin instead of thru the 8 and 6 pin socket on the circuit board.  The heat builds up on the circuit board where socket pins are soldered onto the GPU circuit board.  There are pics on the web of the aftermath of this exact same scenario.

To fix your problem with not enough 8pin outs at your power supply, Simple... They make splitter cables that effectively doubles the amount of 8pin PCIE outputs of your power supply. (Does not double the total output ABILITY of your power supply).  Goto Ebay and use the search term ( PCI-E-6-pin-to-2x-6-2-pin-6-pin-8-pin-Power-Splitter-Cable-PCIE-PCI-Express ) for the cable(s) you need.

 

[Bob-Bit]

You misunderstood then. I am planning on using both the 8 and 6 pin connectors on the GPU, but I'm going to use one of the cables that come with the Corsair power supply that have both an 8 pin and a 6 pin connector that branch off at the GPU end of the cable.

[remauto1187ma]

You misunderstood then. I am planning on using both the 8 and 6 pin connectors on the GPU, but I'm going to use one of the cables that come with the Corsair power supply that have both an 8 pin and a 6 pin connector that branch off at the GPU end of the cable.

That is fine. Thats why they are made like that for.  I have COrsair HX750 power supplies and have some of the same cables you speak of.  They work fine.

[quick1unc]

majority of cards that have 2 power connectors won't operate with just 1 anyways. Even if you undervolt the card and really only need 1 connector for the power requirements, it still needs both to operate. Depending on what your psu has for cables and what card/power requirements you have, you can often get away with an 8 pin splitter to take 1 8 pin from the psu and supply both connections on a card. It important that you know how much voltage your cards are going to run and not just with undervolting as its always possible that the software you use to undervolt ie: afterburner doesn't load properly on a reboot and you are suddenly putting 100% wattage through those connections and overheat them. You just have to plan everything out before you start making and choosing connections.

[remauto1187ma]

I have a 1080 and some 1060's that have dual sockets on them and they all work just fine on the one cable feed split to 8+6 and even an 8+8 on the 1080.