How to power a 2nd 1080ti

[prvfedoctor]

Hi,

I have a 700W power supply and I would like to power a second 1080ti with it. However, my power supply only has one double 8pin (6+2) cable. I'm putting a picture of it in the link bellow.

https://imgur.com/a/4lPs8

I would like to know if it safe to attach a power splitter cable to each of my 8 pin cables in order to have four 8 pin cables and power the second gpu. Something such as this:

https://imgur.com/a/jSqIr

Thank you in advance,
Paulo

[Signaturan]

It is not safe to do that. It will stress or melt that cable if you run the 1080Ti at full power.

[prvfedoctor]

Thank you for the swiftness of your reply.

The power supply also has SATA, PATA and FDD cables.

What do you recommend?

[prvfedoctor]

It also has molex cables.

Can I use a molex to 6 pin adapter and then a 6 pin to a double 8 (6+2) pin adapter? Or is that also unsafe?

[carlo_0000]

if the gpu has only one 8 pin connector  than it s not safe to split it , it s gonna overload

even the 2x8 pin on a good corsair  it s not safe to power 2x gtx1080i a full power
i power 2x 1080 with power limit 75% and got 2 connector burn (when theoretically it s should be ok) i replace the cable  had probably some bad connectors


but if the gpu has   like 8+6   than you can split it one, as you also have the second 6pin  the gpu doesn't need 6 wire for it s own


if you get 3x separate 12v wire from the power supply than yes it s safe does not matter where it come from, you can use molex or sata or cpu connector
but  need to get 3 x 12v  
there are some 2x molex to pci-e adapter,  but it's to week you need to add an 3rd wire, you can do it your own if you have a old broken psu  you remove a pin from there and you plug in in the missing 12v and connect to a 12v of the psu

i see from the pics (you gpu is 2x 6pin?) than you can use 2x molex to pci adapter,
you power each gpu with your current 2x 6pin each one, then the second 6pin you use a molex adapter  so you have 3x12v shared +2x 12v (not shared if possible)
or you power the first one like it s now, and the second one with 2x 6pin molex adapter but less safe (and each molex from the psu may not be shared with something else)
and in this case you should add a 3rd 12v wire in the adapter


but if you only have a 700w you gonna need to powerlimit a lot because psu will shutdown, specially if you have a powerfull cpu
1080ti use more power than you may think


there are some power spikes   theoretically you should be able to power 3x 1080ti with a 700w 80+psu  with 65% power limit

but it won't, i tried  the psu shutdown immediately

i tested with zalman zm-700tx   i testes with power limit 60%  when wattmeter at the wall give you less than 600w it shutdown

more strange it shutdown after 15-20 minute with 2x 1080ti  with power limit at 70%?  when it use less than 500w at the wall  in the 450w if i remember at the wall
did the same test  with an corsair cx650   was not able to handle 2x 1080ti without shutdown but did better than the zalman

the corsair rm750i  is able to handle 2x 1080ti without problem, the psu can get power spike up to 840w without shutdown
i did not the test with 3x 1080ti

you could think the zalman psu is weak but
the psu can Handel 670w+  because it power 5x 1060 +120w cpu just fine around 670w, guess power is more stable there ?

[prvfedoctor]

Dear carlo_0000,

thank you very much for your detailed explanation, I really had no idea.

My 1080ti gpu needs a 8 pin plus a 6 pin.

Can I use a double molex to 8 pin adapter to power the 8 pin and then a sata to 6 pin adapter to power the 6 pin?

Double molex to 8 pin:
https://imgur.com/a/9GsbG

Sata to 6 pin:
https://imgur.com/a/q16QY

There is also a double sata to 6 pin:
https://imgur.com/a/eyqlj

Best regards,
Paulo

[carlo_0000]

yes  but avoid to share the molex wire from the psu with other stuff, in this way you only have 4 x 12V

but it s better to share your existing 2x 8 pin  1 to each gpu (if cable is not to short)  and add an adapter on the 6pin of each gpu

[prvfedoctor]

Dear carlo_0000,

thank you very much for the swiftness of your reply.

I will power each 8 pin of the gpus with the two 8 pin cables that I already have. To power the remaining two 6 pins I will buy two double molex to 6pin adapters and connect one to each card.

Thank you once again.

Best regards,
Paulo

[Amstellodamois]

1. Have you tried powering your 1080s with the 8-pin only? Sometimes, it's enough.

[Zakairdrop]

Hello,

I'm a electronic engineer and I just want to say that it's not safe to do that.

[carlo_0000]

1. Have you tried powering your 1080s with the 8-pin only? Sometimes, it's enough.

i don't think you can only power the 8 pin without the 6 pin, gpu will not boot   and if it will boot, its a very bad idea because you sharing 3x 12v wire for 2 gpu's  it s gonna burn , it s an ti not an 1080   even with the 1080 at full power it s not safe 2x 1080 at full power use above 400w
(have this on my 1080 ring power limit to 74% and got 2 connector burn from a corsair had to change the connector)

Hello,

I'm a electronic engineer and I just want to say that it's not safe to do that.

 for ?

to use the molex adapter to power the 6pin ? it s safe and more than enough the gpu won't be at full power (he cannot anyway his power supply will shutdown)

the existing 8x8 pin can power 300w at lease    so it s shared lets say each gpu get 150w from there , the molex adapter can give 2x75 with the lost in the adapter  let s say 140w   140+150   290w (and did not count the power from the pcie slot   so it s more than enough)

and you can check if the connector or cable get hot or not


i use a lot of adapters never had trouble from there
but i always add the +12v wire what is missing in the molex adapter so i'm always safe


i have some  psu with only 2x2 8pin  and i made lot of adapter  to power 5gpu with 2x6pin  i also used the 8 pin for cpu, with existing wire i could only power 2 gpus when i power 5

[BitMaker2017]

1080ti consumes much more power than regular CPU, so you can use CPU power connector (4x 12v yellow cables & 4x GND cables vs 3x 12v in PCIe connector, 33% more) to power GPU with a CPU-2xPCIe power adapter (available on sale) and use 2xMolex-CPU power cable to power CPU. I think that it's a most safe variant.

[carlo_0000]

1080ti consumes much more power than regular CPU, so you can use CPU power connector (4x 12v yellow cables & 4x GND cables vs 3x 12v in PCIe connector, 33% more) to power GPU with a CPU-2xPCIe power adapter (available on sale) and use 2xMolex-CPU power cable to power CPU. I think that it's a most safe variant.

sure but what you say it false it s not 33% more, don't forget most of time the wire to cpu are smaller than the pcie  so 4 wire doesn't mean better than 3 wire, specially in the poor adapter the wire are ridiculous tin 

and he need to split then because still need to power his cpu

[prvfedoctor]

Thank you for your suggestions, carlo_0000, Signaturan, Amstellodamois, Zakairdrop and BitMaker2017.

I already bought the two double molex to 6pin pci-e adaptors. I will try to connect the 6pin cables on the gpu with them and then I will let you know how it went. I also bought one double molex to 8pin pci-e adaptor, in the event that the two 6+2 pin cabels that I already have are to short and I can't use them to power each 8pin of the gpu.

Thank you all once again for your valuable help.

Best regards,
Paulo

[BitMaker2017]

Thank you for your suggestions, carlo_0000, Signaturan, Amstellodamois, Zakairdrop and BitMaker2017.

I already bought the two double molex to 6pin pci-e adaptors. I will try to connect the 6pin cables on the gpu with them and then I will let you know how it went. I also bought one double molex to 8pin pci-e adaptor, in the event that the two 6+2 pin cabels that I already have are to short and I can't use them to power each 8pin of the gpu.

Thank you all once again for your valuable help.

Best regards,
Paulo

Be carefull with double molex to 8pin pci-e adaptor, I burned one such :-)
The wires survived but there was a bad contact in the slot

[BitMaker2017]

1080ti consumes much more power than regular CPU, so you can use CPU power connector (4x 12v yellow cables & 4x GND cables vs 3x 12v in PCIe connector, 33% more) to power GPU with a CPU-2xPCIe power adapter (available on sale) and use 2xMolex-CPU power cable to power CPU. I think that it's a most safe variant.

sure but what you say it false it s not 33% more, don't forget most of time the wire to cpu are smaller than the pcie  so 4 wire doesn't mean better than 3 wire, specially in the poor adapter the wire are ridiculous tin 

and he need to split then because still need to power his cpu

All yellow cables in both my PSUs are marked as 18AWG, so it's true in my case: 3 + 33% = 4. Maybe not all the PSUs are done this way

[szafa]

Buy better psu with 2 line 8 pin.

[prvfedoctor]

Hi,

I was able to connect the 2nd 1080ti aero. I used the two 6+2 connectors to power each 8 pin of the gpus and the double molex to 6 pin adaptors to power each 6 pin of the gpus. I have one image here:

https://imgur.com/a/2PhHp

The gpu directly connected to the motherboard is mining zcash at 700 sols and the gpu connect with the riser is mining zcash at 670 sols. Is this difference normal? I have an image here:
https://imgur.com/a/ALkeB


Also, I have average temperatures of 83ºC in each card, is this ok?

Best regards,
Pauçp

[zorachus99]

Hi,

I was able to connect the 2nd 1080ti aero. I used the two 6+2 connectors to power each 8 pin of the gpus and the double molex to 6 pin adaptors to power each 6 pin of the gpus. I have one image here:

https://imgur.com/a/2PhHp

The gpu directly connected to the motherboard is mining zcash at 700 sols and the gpu connect with the riser is mining zcash at 670 sols. Is this difference normal? I have an image here:
https://imgur.com/a/ALkeB


Also, I have average temperatures of 83ºC in each card, is this ok?

Best regards,
Pauçp

It's interesting that many people told you not to do this, and you ignored them.  Yet you come back and ask is 83C is an abnormal temperature?   

[carlo_0000]

you can put the fan lot faster with ati afterburner

even if fan need full speed it s better to try keep under 70°c, better need to change the fan in a year or 2 than a dead gpu because it was to hot

also move you hard drive from there it s gonaa get hot and die  put it somewhere up close to you dvd


and the molex adapter are the 2 molex connected to the same cable ? if yes then it s not good you need 2 yellow wire from the psu at lease
or keep your power limit lower than 62%