No Spare PCI-E Cable, Need to Power an 8-Pin GPU

[Collider]

So I'm using all available PCI-E 8 Pin connectors on my EVGA 850 BQ and need to connect 1 more GPU that takes another 8 Pin connector.

Which option is better and safer?

1) Use Molex to PCI-E Adapter like this one, In this case I would use 2 separate 12v rails to power each of the molex's. The only thing that has me worried here is that the adapter is 18 AWG and not lower.

or

2) Use a 6-Pin to 8-Pin adapter, but in this case I would be running 2 GPU's on a single PCI-E rail

or

3) Use spare 2nd CPU rail with an adapter like this

 

[Elixer]

How many watts are you currently using?
Which GPUs are you running now, and what is the new one?

 

[Collider]

I'm running 3 x Sapphire Nitro (non +) RX 470 and want to add a 4th identical card.

I have a separate PSU that powers MOBO, CPU and HDD, So this 2nd PSU will only be running these 4 cards.

If I had to estimate it is probably pulling around 400-450 watts running 3 cards, so with 4th one it will be around 550-600 watts, which should be fine for an 850 watt PSU.

 

[Elixer]

I would be worried about 18AWG as well since it can only handle 10 Amps, and it looks like those adapters are using 18AWG, so...

The first link is what most video card companies offer in their box, so, I would most likely go that route.

 

[MrTeal]

Putting another card on the other connector of a PCI-e single cable makes it susceptible to melting that cable at the PSU end; I wouldn't power two full cards off one modular cable.

Electrically, your best bet is to use the 8 pin EPS to 8 pin PCI-E adapter. At least that way you're pulling power through three wires and connector pins. With the dual molex adapter, you're pulling all the 12V current through two wires on the peripheral cable and two pins on the end of the connector that plugs into the supply. Added bonus, the CPU cable is hardwired so it's no additional wiring mess and hardwired cables are more robust anyway.

That being said, if each card is pulling 150W, running one off a dual molex adapter should be fine and it's likely you have a bunch of them laying around anyway, so it's basically free and doesn't require waiting for shipping.

 

[Guru]

Either one would be okay. Neither is a perfect solution, but all would work.

 

[Collider]

Thanks for the replies guys.

To play it safe I think I will use 2 separate 12v Molex lines from PSU to power the 2xMolex-to-PCIe, this way the load is split. So it will be 2 separate 12v lines powering 1 GPU. I think its the safest approach.

I also have 1 more GPU after that that needs powering. For this additional GPU I decided to use a spare CPU line with 8 pin EPS to 8 pin PCI-E adapter, as @MrTeal suggested.

This way both GPU's will have 2 12v lines powering them.

 

[TemjinGold]

Why not power the 4th card through that separate PSU?