Question Single or dual 8-pin CPU power

[Freyeth]

Hello.
Can You please help me with an issue?
I plan changing Motherboard and CPU for 7800X3D and ASUS X670E-PLUS GAMING. Thr motherboard has two 8-pin CPU power plugs, while my PSU (850W) has only one cable of that kind. It is said nowhere in the manual of the MoBo that both are or are not required for it to work. What is the truth in that case?

 

[Misgar]

The general rule is you only need one 8-pin EPS12V lead plugged in, unless you intend to do some serious overclocking. Check your motherboard manual to see if it recommends a specific socket when only one lead is used.

The ancient computer I'm using at this moment in time has a single 8-pin connector on the motherboard, but the power supply only has a 4-pin lead. The PC works fine, but I'm not overclocking the CPU.

Fewer 0V and 12V wires in parallel result in greater volt drops down the EPS12V cable. More wires reduce the volt drop at increased current levels. If your CPU pulls 300W in a heavy overclock, it will draw 25A at 12V from the EPS lead (25 x 12 = 300W).

If the wires used in an EPS cable are 16AWG, each wire is rated to carry up to 15A. Hence two 12V wires in parallel can in theory supply up to 30A @ 12V or 360W. Unfortunately, the volt drop down just two wires would probably result in an unstable CPU, due to large fluctuations in voltage as the current changes.

To increase stability and reduce volt drop, power supply manufacturers add extra wires on higher rated PSUs. Hence some supplies have two 8-pin EPS12V cables, others have an 8-pin + 4-pin. Your PSU has a single 8-pin cable, mine has a single 4-pin cable.

 

[Dj0gany]

Each 8pin EPS can deliver around 300W of power to your CPU.
The 7800X3D is not power hungry at all, the max it consumed was 90W while being stress tested.

AMD Ryzen 7 7800X3D Review: New Gaming Champ Beats Pricier CPUs

Sub-$450 CPU is even faster for gaming than Ryzen 9 7950X3D.

www.tomshardware.com

"Our highest average power measurement for the Ryzen 7 7800X3D was 86W, showing that it runs well below the rated 120W TDP. "
You are perfectly fine with only one 8 PIN EPS connector plugged in.

 

[Freyeth]

The general rule is you only need one 8-pin EPS12V lead plugged in, unless you intend to do some serious overclocking. Check your motherboard manual to see if it recommends a specific socket when only one lead is used.

The polish ASUS tech support (I'm from Poland) said that according to the manual both are required for MoBo to operate...which information is mentioned nowhere

 

[Eximo]

The polish ASUS tech support (I'm from Poland) said that according to the manual both are required for MoBo to operate...which information is mentioned nowhere

That would be atypical, but you did buy a very premium board.

If the PSU is modular, you should be able to order another EPS cable from the manufacturer or from someone like Cablemod.