Connecting 6 GPUs to 2 PSUs, please, help... - page 2.

Eastwind

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Activity: 896

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Quote from: spinx on February 10, 2014, 11:00:18 AM

Quote

You have to connect ALL the riser molex to the main PSU.

# 1 - Corsair CX750
* Motherboard 100W
* 1 GPU = 1 * 75 = 75W
* 6 PCIE slot (4+2)*75W = 450W
* Fans 10W
(total = 100+75+450W +10W = 635W 85% of 750W)

# 2 - Fractal R2 750W
* 5 GPU = 5 * 75W = 375W
* (5x 6pin + 0molex)
(total about 50% of 750W)

Like this?

The only problem i have then is regarding PSU #2, the Fractal R2. It has 2 rails and limited connectors, im thinking like this:

Rail #1 - 30amp*12V=360W
1x pci-e (1*75W)
6x molex -> 3x pci-e 6pin (3*75W=225W)
= 300W for 4pcs 6pin

Rail #2 - 30amp*12V=360W
1x pci-e (1*75W) -> 2 x 6pin (will make this converter myself)
OR
1x EA12V -> 6pin?

Your picture is right indication of the set up.

For fractal R2, you can use the 4*6pin from Rail1 and one from the EA12V->6pin. I do not know the distribution of power between rails. I just assume Rail 1 is the 4*(6+2)pin+peripheral, and Rail 2 is the MB connector +CPU12V.

It is better to use two CTX750 if you have not bought the Fractal.

spinx

full member

Activity: 139

Merit: 100

Quote

You have to connect ALL the riser molex to the main PSU.

# 1 - Corsair CX750
* Motherboard 100W
* 1 GPU = 1 * 75 = 75W
* 6 PCIE slot (4+2)*75W = 450W
* Fans 10W
(total = 100+75+450W +10W = 635W 85% of 750W)

# 2 - Fractal R2 750W
* 5 GPU = 5 * 75W = 375W
* (5x 6pin + 0molex)
(total about 50% of 750W)

Like this?

The only problem i have then is regarding PSU #2, the Fractal R2. It has 2 rails and limited connectors, im thinking like this:

Rail #1 - 30amp*12V=360W
1x pci-e (1*75W)
6x molex -> 3x pci-e 6pin (3*75W=225W)
= 300W for 4pcs 6pin

Rail #2 - 30amp*12V=360W
1x pci-e (1*75W) -> 2 x 6pin (will make this converter myself)
OR
1x EA12V -> 6pin?

Eastwind

hero member

Activity: 896

Merit: 1000

Quote from: spinx on February 10, 2014, 08:51:05 AM

Quote from: Eastwind on February 10, 2014, 08:43:16 AM

Quote from: spinx on February 10, 2014, 07:02:10 AM

I have almost the same problem, running 6pcs 270 cards with 2PSU's
https://bitcointalksearch.org/topic/m.5043351

Problem is that my 270's only have one 6pin-connector on the pcb, this allows 75W. The 270 needs about 150W each so the other 75W needed has to come from motherboard/powered riser. That means in my case 6 x 75W = 450W from molex on the risers, and most PSU's only have the molex/sata connectors on 1 rail, and very few PUS's allow 450W on 1 rail. Therefore i need to split the 450W load on 2 PSU, but even 225W is not possible on my PSU (molex on 1 rail, allowing 18Amps, 12V*18Amp = 216W, wich means im 9W short...?)

I belive i need to buy a new PSU with a singel 12V rail, like the Corsair CX750, 62AMP on 12V = 744W on 1 rail.

The solution is to buy a single rail PSU.

You can also undervolt.

Yes i belive this is my solution? I will buy a CX750 today.

6 x R9 270
# 1 - Corsair CX750 (1x rail 12V = 744W)
# 2 - Fractal R2 750W (2x Rail 12V * 30amp = 360W * 2 = 720W)

# 1 - Corsair CX750
* Motherboard 150W
* 2 GPU = 4 * 75 = 300W
* (2x + 6pin 2molex)
* Fans 10W
(total about 62% of 750W)

# 2 - Fractal R2 750W
* 4 GPU = 8 * 75W = 600W
* (4x 6pin + 4molex)
(total about 80% of 750W)

You have to connect ALL the riser molex to the main PSU.

# 1 - Corsair CX750
* Motherboard 100W
* 1 GPU = 1 * 75 = 75W
*
6 PCIE slot
(4+2)*75W = 450W

* Fans 10W
(total = 100+75+450W +10W = 635W 85% of 750W)

# 2 - Fractal R2 750W
* 5 GPU = 5 * 75W = 375W
* (5x 6pin + 0molex)
(total about 50% of 750W)

Eastwind

hero member

Activity: 896

Merit: 1000

Quote from: bananahunter67 on February 10, 2014, 08:45:52 AM

What about only 3 cards of 6 being connected woth powered molex, is it OK or I need to connect all 6? AFAIK 3 GPUs can sometimes run without powered molex, so is it OK?

If you have enough molex connectors from the PSU, then connect all 6. It is OK to connect only 3.

spinx

full member

Activity: 139

Merit: 100

Quote from: Eastwind on February 10, 2014, 08:43:16 AM

Quote from: spinx on February 10, 2014, 07:02:10 AM

I have almost the same problem, running 6pcs 270 cards with 2PSU's
https://bitcointalksearch.org/topic/m.5043351

Problem is that my 270's only have one 6pin-connector on the pcb, this allows 75W. The 270 needs about 150W each so the other 75W needed has to come from motherboard/powered riser. That means in my case 6 x 75W = 450W from molex on the risers, and most PSU's only have the molex/sata connectors on 1 rail, and very few PUS's allow 450W on 1 rail. Therefore i need to split the 450W load on 2 PSU, but even 225W is not possible on my PSU (molex on 1 rail, allowing 18Amps, 12V*18Amp = 216W, wich means im 9W short...?)

I belive i need to buy a new PSU with a singel 12V rail, like the Corsair CX750, 62AMP on 12V = 744W on 1 rail.

The solution is to buy a single rail PSU.

You can also undervolt.

Yes i belive this is my solution? I will buy a CX750 today.

6 x R9 270
# 1 - Corsair CX750 (1x rail 12V = 744W)
# 2 - Fractal R2 750W (2x Rail 12V * 30amp = 360W * 2 = 720W)

# 1 - Corsair CX750
* Motherboard 150W
* 2 GPU = 4 * 75 = 300W
* (2x + 6pin 2molex)
* Fans 10W
(total about 62% of 750W)

# 2 - Fractal R2 750W
* 4 GPU = 8 * 75W = 600W
* (4x 6pin + 4molex)
(total about 80% of 750W)

bananahunter67

sr. member

Activity: 392

Merit: 265

What about only 3 cards of 6 being connected woth powered molex, is it OK or I need to connect all 6? AFAIK 3 GPUs can sometimes run without powered molex, so is it OK?

Eastwind

hero member

Activity: 896

Merit: 1000

Quote from: spinx on February 10, 2014, 07:02:10 AM

I have almost the same problem, running 6pcs 270 cards with 2PSU's
https://bitcointalksearch.org/topic/m.5043351

Problem is that my 270's only have one 6pin-connector on the pcb, this allows 75W. The 270 needs about 150W each so the other 75W needed has to come from motherboard/powered riser. That means in my case 6 x 75W = 450W from molex on the risers, and most PSU's only have the molex/sata connectors on 1 rail, and very few PUS's allow 450W on 1 rail. Therefore i need to split the 450W load on 2 PSU, but even 225W is not possible on my PSU (molex on 1 rail, allowing 18Amps, 12V*18Amp = 216W, wich means im 9W short...?)

I belive i need to buy a new PSU with a singel 12V rail, like the Corsair CX750, 62AMP on 12V = 744W on 1 rail.

The solution is to buy a single rail PSU.

You can also undervolt.

spinx

full member

Activity: 139

Merit: 100

I have almost the same problem, running 6pcs 270 cards with 2PSU's
https://bitcointalksearch.org/topic/m.5043351

Problem is that my 270's only have one 6pin-connector on the pcb, this allows 75W. The 270 needs about 150W each so the other 75W needed has to come from motherboard/powered riser. That means in my case 6 x 75W = 450W from molex on the risers, and most PSU's only have the molex/sata connectors on 1 rail, and very few PUS's allow 450W on 1 rail. Therefore i need to split the 450W load on 2 PSU, but even 225W is not possible on my PSU (molex on 1 rail, allowing 18Amps, 12V*18Amp = 216W, wich means im 9W short...?)

I belive i need to buy a new PSU with a singel 12V rail, like the Corsair CX750, 62AMP on 12V = 744W on 1 rail.

Eastwind

hero member

Activity: 896

Merit: 1000

You are right. However you can connect ALL the molex to the main PSU. Never connect the molex to 2nd PSU (if they are not cut).

bananahunter67

sr. member

Activity: 392

Merit: 265

Hey guys,

I am building my first rig, 6 GPUs Gugabyte R9 170, with a Gigabyte motherboard and 2 PSUs Evga Nova Gold, each PSU by 750 watts.
The PSUs are connected between them with an add2psu module.
Now i am wondering how to connect the cards.

So far I have connected all the stuff this way:

1. 1st PSU connnected to MB
2. 2nd PSU connected to 1st PSU via add2psu
3. 1st PSU connected to 3 of the cards with common main cards cables
4. 2nd PSU connected to the other 3 of the cards with common main cards cables
5. 1st PSU connected as well to 3 of the cards with the molex of the riser cables.
6. The 3 cards connected to the second PSU are not connected with their molexes to anything, just with the main cables to the second PSU.
7. If this also is important, one of the cards is directly put into the MB, the other 5 are connected via risers.

Is this correct and if not what should I consider as a change?

Any advice welcome and thanks in advance

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