Using 2x8 pin PCIe cables for RTX 4090

G

GameDos

Member
Hi,

When I bought my desktop, I requested PCSpecialist install "two additional separate 8-pin PCIe power cables" so I can plug them into my GPU (not part of the order) without having to do the cable management. My current GPU is an ASUS TUF RTX 3090 OC edition.

I will no longer be able to use that card within a couple of months so I plan on upgrading to an RTX 4090. I might just go for an ASUS TUF Gaming GeForce RTX 4090 OC Edition since I am already using the 3090 version.

My concern, however, is about cable management for power. Will I be able to use my currently installed power cables and simply hook them to an adapter to power the 4090 card?

My PSU is the "HX 1200 Watt 80 PLUS PLATINUM Certified Fully Modular PSU".
 
T

TonyCarter

VALUED CONTRIBUTOR
How many cables are currently powering the GPU? Is it 3 or 4 from the PSU into 1 or 2 adapters to the 2 x 8-pin?

The GPU should come with a 4-to-1 power connector/adapter like this...
16-pin-adapter2.jpg

...which you can just plug in the normal 8-pin power cables...you may not need all 4 connected to power it though, but see what the manual says based on your power requirements (i.e. only really need the full 4+PCIe slot for heavy overclocking).

My 4090FE worked with 3 (no signal with just 2 ), and the supplied cable/adapter has an active circuit to detect whether 3 or 4 are powered and then limits the cards power draw to the max the amount will support.
 
G

GameDos

Member
TonyCarter said:
How many cables are currently powering the GPU? Is it 3 or 4 from the PSU into 1 or 2 adapters to the 2 x 8-pin?

The GPU should come with a 4-to-1 power connector/adapter like this...
16-pin-adapter2.jpg

...which you can just plug in the normal 8-pin power cables...you may not need all 4 connected to power it though, but see what the manual says based on your power requirements (i.e. only really need the full 4+PCIe slot for heavy overclocking).

My 4090FE worked with 3 (no signal with just 2 ), and the supplied cable/adapter has an active circuit to detect whether 3 or 4 are powered and then limits the cards power draw to the max the amount will support.
Click to expand...
My 3090 is powered by 2 cables, each 8-pin.
 
T

TonyCarter

VALUED CONTRIBUTOR
GameDos said:
My 3090 is powered by 2 cables, each 8-pin.
Click to expand...
In that case you'll need to fit at least another one - 450W GPU to allow for 3 x 150W from the PSU + 75W from the MB (525w max).

The 3090 being a 350W GPU means 2 x 150w from the PSU + 75w from MB was sufficient (375w max).
 
Last edited:
T

TonyCarter

VALUED CONTRIBUTOR
GameDos said:
Why? Asus TUF 4090 needs 1x16?
Click to expand...
1x16 at the GPU end, but 3 or 4 at the PSU end. That's what the included adapter is for!

Each PCIe rail on your PSU provides upto 150w, and the motherboard GPU slot up to 75w - for a total of 375w max.

To deliver the 450w needed for the 4090 you could get 75w from the motherboard GPU slot, so would need to find 375w from the PSU - so 2 x 150w cables does not get you there, hence the need for 3 for normal use, and possibly 4 if you're going to overclock the GPU further.
 
SpyderTracks

SpyderTracks

We love you Ukraine
4090 can consume as much as 600w, hence why the 4 8pin connectors.

On modern ATX3 PSUs they have a 12 pin port on the PSU, you’ve got the older ATX 2 model which only has 8 pin PCIe power ports
 
G

GameDos

Member
TonyCarter said:
1x16 at the GPU end, but 3 or 4 at the PSU end. That's what the included adapter is for!

Each PCIe rail on your PSU provides upto 150w, and the motherboard GPU slot up to 75w - for a total of 375w max.

To deliver the 450w needed for the 4090 you could get 75w from the motherboard GPU slot, so would need to find 375w from the PSU - so 2 x 150w cables does not get you there, hence the need for 3 for normal use, and possibly 4 if you're going to overclock the GPU further.
Click to expand...
so even if I used a daisy chain, I can only get 150W from the 16-pin (2x8 same cable) connection?
 
G

GameDos

Member
TonyCarter said:
1x16 at the GPU end, but 3 or 4 at the PSU end. That's what the included adapter is for!

Each PCIe rail on your PSU provides upto 150w, and the motherboard GPU slot up to 75w - for a total of 375w max.

To deliver the 450w needed for the 4090 you could get 75w from the motherboard GPU slot, so would need to find 375w from the PSU - so 2 x 150w cables does not get you there, hence the need for 3 for normal use, and possibly 4 if you're going to overclock the GPU further.
Click to expand...

in page 9, they mention "In the “SINGLE” position, the full output of the power supply’s +12V rail is available to any and all connectors, while in the “MULTIPLE” position, each individual connector has Over-Current Protection so no more than 40A of current can be delivered on any given cable."

does that not mean each rail no longer is capped to 150W?
and since the pcie cables are compatible with up to 288 W per cable, 2 cables can deliver enough wattage for non-OC 4090?
 
Last edited:
T

TonyCarter

VALUED CONTRIBUTOR
GameDos said:
so even if I used a daisy chain, I can only get 150W from the 16-pin (2x8 same cable) connection?
Click to expand...
An ATX2 PSU will only deliver 150w per PCIe socket, so no matter how many times you split and/or rejoin, you'd only ever get 150w per channel.

2 cables out of 2 ATX2 PSU sockets will give you 300w, 3 cables will give you 450w, 4 cables will give you 600w.

2024-06-28_15-37-23.jpeg
 
You must log in or register to reply here.
Top