7 x 470's lowvolt/1500 mem straps on one evga 1300w

[Tuner77]

Any power gurus out there? I'm trying to be safe by researching first, but can't find this specific situation.

I have an MB with 7 x PCIE lanes running Sapphire Nitro OC 470 4GB's using the low volt and 1500 mem straps, so they show 75w in afterburner. If I understand correctly, that's just from the 8-pin GPU plug, and there's another 40w (up to 75w with regular mem straps) being drawn from the PCIE slots via the usb risers powered by sata>molex adapters, so 110w is often reported by users with similarly configured cards ATW.

110 x 7 = 770watts. Add in some for the MB/CPU/MEM/HD, etc and it seems like there's plenty of room to power that on an 1300w evga, even though I know some people prefer 70% max (I'm okay with 80%).

I have the rig up and running with 6 x, but to add the seventh, I'll need to power the card by splitting off from one of the lines currently powering one of the existing six. Or use y-splitters to share power from two of the existing six. Will either of those ideas work? Will the card(s) just not function if there's inadequate wattage supplied, or is there real risk of wire melting or other damage?

Here's my understanding and plan:

1) I read 40w per molex with just two wires on standard PSUs. My EVGA sata lines seem to have five wires, but I don't know if that's two sets of two wires (and an extra ground) = 80w, or if it's four powered lines and one shared ground = 160w. I can't find detailed wattage per cable/connector for EVGA, so I'm assuming 80w to be safe.

2) My VGA/GPU lines have 8 lines, but I don't know if that's three sets of two wires (plus two extra grounds) = 120w or much more (160w, 240w?). I'm assuming 120w to be safe.

3) My plan is to try to share the wattage from two of the sata lines (five-wires) currently powering one 470 riser each, and share the wattage from two of the VGA lines (8 wires) currently powering one 470 GPU plug each. But

I'm hesitant to proceed without asking for advice because I can't find exact information on this from other users, nor detailed wattage per line on the evga 1300w PSU. I read somewhere that all PSU power comes from a single place in the PSU, so you can't go wrong supplying too much wattage via y-cabling (assuming it's the right voltage, with I believe the risers and the VGA/GPU plus are all 12v). But I don't know if I trust that.

And is this even necessary? Can I just use a 6-pin to 8-pin adapter and convert one of my 8-pin gpu lines (that has an extra 6-pin already branched off) to power the GPU, and then just connect one of my SATA > Molex adapters into the many available connectors already on my existing SATA lines (currently feeding one riser each, which might be cable over-kill if they can actually power two or three each).

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[adaseb]

Read

https://forum.ethereum.org/discussion/9495/the-correct-way-of-powering-the-risers-for-the-470-480/p1

From the beginning

[deadsix]

...............
And is this even necessary? Can I just use a 6-pin to 8-pin adapter and convert one of my 8-pin gpu lines (that has an extra 6-pin already branched off) to power the GPU, and then just connect one of my SATA > Molex adapters into the many available connectors already on my existing SATA lines (currently feeding one riser each, which might be cable over-kill if they can actually power two or three each).

Short answer : Yes, you can safely use the 6 pin to 8 pin adapter and power 2 cards off of each cable since the power draw from the PCIe power cables is pretty low for the RX series.
But for the risers its not recommended to use the sata > molex connectors that come with them because they are of bad quality and tend to burn under load, which they will be under on the RX 470/480. Use only Molex cables to power the risers, and if you do not have enough Molex cables, then buy EVGA Molex cables. Plug them in instead of the sata cables on your PSU, you don't need more than that one sata power cables for the ssd. And dont worry about "plug only one riser per cable" if you plan on staying on those clocks. If your GPUZ power draw goes above 100W then you may need to have only one card per molex cable.

[Tuner77]

Read

https://forum.ethereum.org/discussion/9495/the-correct-way-of-powering-the-risers-for-the-470-480/p1

From the beginning

Working my way through it. Thanks, adaseb; I had read early ref and third party 480's had a problem but saw a bios update supposedly fixed that. I didn't dig in further, but will now seeing that it was originally 4-5Amps.

My sata>molex cables are cool to the touch running 1 riser per cable for 24 hours with brand new cards, but I still want to be safe. It sounds like the extra 12v CPU line could be re-wired for that last card, or jump off one of the extra 6-pin lines for the riser, and use the other extra 6-pin from a separate cable to go to an 8-pin for the card power slot. Does that make sense?

[Tuner77]

buy EVGA Molex cables.

Dont worry about "plug only one riser per cable" if you plan on staying on those clocks. If your GPUZ power draw goes above 100W then you may need to have only one card per molex cable.

Thanks! More things to buy, but safer. And it sounds like I can get 7 cards total. Is it possible to split the load across two molex power cables? So each cable powers one card, and then one of the extra ports on each cable is used with a y-connector to power the third card?  Also, my PSU's molex lines have four wires, but most of the ones I see online in y-adapters and other extenders only have two wires. With four wires to a molex, that's supplying twice the power, right? So 40w x 2 sets of wires = 80w, whereas amazon two-wire adapters are only giving 40w.

[adaseb]

Read

https://forum.ethereum.org/discussion/9495/the-correct-way-of-powering-the-risers-for-the-470-480/p1

From the beginning

Working my way through it. Thanks, adaseb; I had read early ref and third party 480's had a problem but saw a bios update supposedly fixed that. I didn't dig in further, but will now seeing that it was originally 4-5Amps.

My sata>molex cables are cool to the touch running 1 riser per cable for 24 hours with brand new cards, but I still want to be safe. It sounds like the extra 12v CPU line could be re-wired for that last card, or jump off one of the extra 6-pin lines for the riser, and use the other extra 6-pin from a separate cable to go to an 8-pin for the card power slot. Does that make sense?

Yes do that and don't use the SATA anymore. It will melt.

[bardacuda]

A couple good rules of thumb:

The fewer connectors the better. Every splitter/extension/etc. adds another point of contact which means more chance of extra resistance and/or arcing and therefore more chance of fire/excess heat

Never use SATA power for anything other than SATA disk drives. Use molex or PCI-E 6-pin to power all of your risers. Stick to one molex chain for every two risers.

Now as far as using splitters to split 6-pins into 8-pins, and 8-pins into dual 8-pins, etc, you should keep a few things in mind. Every 6-pin is good for up to 75W and every 8-pin is good for up to 150W. So let's say you have two cards that each draw 125W. Let's say they are getting ~50W out of the powered riser. In that case, each card needs an extra 75W. You could split one 8-pin into two 6-pins and rest easy. If you split a 6-pin into two 6-pins then you could be loading the cable 2x over spec. This should be no problem for the PSU itself as long as you have enough amperage available on the 12V rail. You probably have a single 12V rail anyway, so as far as the PSU is concerned, it's not working any harder. The difference is that you are going to have double the amperage running through the wire between the PSU and the video card. Now a wire's amperage rating depends on a lot of factors including diameter, length, and how tightly packed/how much air flow it is getting. If you have short, individually-sleeved wires running in front of your intake fans you are probably fine. If you have long, lower-gauge wires with extensions, all zip-tied into tight bundles packed up against other current-carrying wires or bundled into mesh sleeves you are going to have higher resistance and bad airflow - so that's bad. Basically, as long as the wires stay cool enough, you're fine.

[elzium]

my PSU's molex lines have four wires, but most of the ones I see online in y-adapters and other extenders only have two wires. With four wires to a molex, that's supplying twice the power, right? So 40w x 2 sets of wires = 80w, whereas amazon two-wire adapters are only giving 40w.

Thats the problem if wires dont have colors anymore, guesswork and weird theories. Molex has ground and +5V and +12V, so if u have two wires u missing some of that and usb riser wont work.
But before goin shopping, use anything that is in ur hand and see if u even get 7th card to work, nothing will melt if u just test. And then, see how u can do it correctly.

BTW that link before, that dont work either on usb riser cause its missing red wire.

[Tuner77]

A couple good rules of thumb:

The fewer connectors the better. Every splitter/extension/etc. adds another point of contact which means more chance of extra resistance and/or arcing and therefore more chance of fire/excess heat

Never use SATA power for anything other than SATA disk drives. Use molex or PCI-E 6-pin to power all of your risers. Stick to one molex chain for every two risers.

Now as far as using splitters to split 6-pins into 8-pins, and 8-pins into dual 8-pins, etc, you should keep a few things in mind. Every 6-pin is good for up to 75W and every 8-pin is good for up to 150W. So let's say you have two cards that each draw 125W. Let's say they are getting ~50W out of the powered riser. In that case, each card needs an extra 75W. You could split one 8-pin into two 6-pins and rest easy. If you split a 6-pin into two 6-pins then you could be loading the cable 2x over spec. This should be no problem for the PSU itself as long as you have enough amperage available on the 12V rail. You probably have a single 12V rail anyway, so as far as the PSU is concerned, it's not working any harder. The difference is that you are going to have double the amperage running through the wire between the PSU and the video card. Now a wire's amperage rating depends on a lot of factors including diameter, length, and how tightly packed/how much air flow it is getting. If you have short, individually-sleeved wires running in front of your intake fans you are probably fine. If you have long, lower-gauge wires with extensions, all zip-tied into tight bundles packed up against other current-carrying wires or bundled into mesh sleeves you are going to have higher resistance and bad airflow - so that's bad. Basically, as long as the wires stay cool enough, you're fine.

Very useful! How about splitting one 8pin into an 8pin for one card, and a 6pin (via existing split on the cable) connected to an 8pin adapter for the second card. That's still just splitting an 8pin right? Only the second card's power travels over a 6pin line for a short distance.  Each card's riser would be powered with its own molex line (or two per molex max).

Where did you find watts per 6pin and 8pin? It seems to vary from PSU to PSU (older ones mainly). I wanted a clear guide on per cable wattage and couldn't find it. Thanks for the tips! My wires are all cold or slightly warm at full OC for 24 hours, but I'm going to change anyways to be safe. Good idea to test 7th first.

[bardacuda]

https://en.wikipedia.org/wiki/PCI_Express#Power

[Tuner77]

Stick to one molex chain for every two risers.

Every 6-pin is good for up to 75W

Wait, if it's 50w each riser is pulling, isn't that 100w for two? My PSU molex chains are connected to the PSU with a 6pin (75w per above). Isn't that overloading it?

[bardacuda]

By 6-pin and 8-pin I mean the end that connects to devices...not the PSU end. So just talking about PCI-E connectors here not Molex. With the risers, there is still a path for power through the motherboard and riser. The molex just adds another path for power in parallel, so not all of the power coming into the card from the bottom is going through the molex cable. Even if it is carrying a little more current than it's supposed to be according to specifications...specs have safety margins built-in already so it's not an absolute maximum. In reality two risers powered by one molex chain isn't going to melt anything. If you're worried about that you could always limit yourself to one molex per riser.

[Tuner77]

By 6-pin and 8-pin I mean the end that connects to devices...not the PSU end. So just talking about PCI-E connectors here not Molex. With the risers, there is still a path for power through the motherboard and riser. The molex just adds another path for power in parallel, so not all of the power coming into the card from the bottom is going through the molex cable. Even if it is carrying a little more current than it's supposed to be according to specifications...specs have safety margins built-in already so it's not an absolute maximum. In reality two risers powered by one molex chain isn't going to melt anything. If you're worried about that you could always limit yourself to one molex per riser.

I get it. The usb cable is also providing power via the pcie-1x card/mb, so that more than covers it with two risers sharing a 6pin to molex line. Thanks!

[bardacuda]

Honestly I am not an expert on all of this but I do know a bit so I just wanted to give you a bit better understanding and more concrete numbers to base your wiring solution off of. Looking at the wiki for Molex though, I am seeing 11A per pin. Since it is @ 12V, this translates to 132W of power. If you look at it this way, one molex chain should be good to provide 66W of power to two cards. Although a card can draw up to 75W through the PCI-E slot, keep in mind that it is sharing some of the load with the mobo/riser.

If you really want to get better/more specific advice I'd suggest the forums at http://www.jonnyguru.com/. These guys know their shit.

Err I just realized you were talking about risers with USB cables but I was thinking about ribbon cables when talking about load sharing...so disregard that part. The USB cables are only used for signal pins and don't actually provide any power, so in that case all of the power would need to go through the molex. Still though, 1 molex chain per 2 risers is fine.

[xxcsu]

On one of my rig Im runnig 7 x rx 480 on AsRock H97 Anniversary with my own custom modded bioses , and 1X/16X multiplier riser card . Total hashing power is around 210 MH/s , and the whole system is pulling 1164 watts at the wall from a US 120 Volts outlet . I can reducing the memory voltage with wattman for each gpu , then the system total power draw will be under 1000Watts

[Tuner77]

Thanks guys! I appreciate the info. That power monitor looks better than my wall mount lcd one. I talked to another guy building a similar system who said the sapphire 470 4gb's don't pull as much through the riser as others. Still trying to verify if that all got fixed when amd updated drivers a while back. Hate to waste money. My connectors weren't but a little warm. Some the wires to the molex plug were outright cold while running.