Motherboard has 8pin+4pin CPU connectors but PSU has only 4+4pin ?

[ORLY]

Hi! So, I almost chose the Corsair RM650i/750i PSU but then found out it had only one CPU power connector which is 4+4pin.
Seasonic Focus Plus Gold/Platinum 650W also has only one 4+4pin cable, to have two 4+4pin cables you need to buy at least a 750W PSU. The same goes for be quiet! Straight Power 11 - 650W has one 4+4pin cable, 750W has one "P8" (8pin I suppose) and one "P4+4" connector.

At the same time, all the better motherboards (AsRock X470 Taichi, ASUS Crosshair VI Hero etc.) have one 8pin connector AND one 4pin connector to supply a CPU. Which means with a 650W PSU (or even a Corsair RM750i) you're able to use only the 8pin connector, because your PSU only has one, leaving the 4pin connector on your motherboard not used.

What's the deal with that? If the second (4pin) 12V connector wasn't needed at all - they wouldn't add it to the motherboards, right? And to plug both 8pin and 4pin connectors I need to buy either a Corsair RM850i (since even the 750W one has only one 12V connector) or at least a 750W PSU from some other manufacturer.

 

[Bones]

That's probrably right, you'd have to buy a 750W to use a board with those connectors.
Good thing is quality 750W PSU's aren't that expensive, this being one that's cheap yet of good quality. https://www.newegg.com/seasonic-foc...x-750w/p/N82E16817151187?Item=N82E16817151187

As to the "Why", maybe someone else knows - Honestly I've never noticed that but again I've always had a 750W or larger unit in use too.

 

[Wavetrex]

You can connect the 8pin only using those 4+4 and forget about the other one.

The extra +4 (or even +8 on ultra-high-end boards) is for extreme overclocking (aka LN2) and can be safely ignored.

I have no idea what the purpose of 750W PSU's and up are these days, especially on mainstream platform.
- CPU consumes at most 150W, and that is when heavily overclocked
- GPUs have become quite efficient and other than the ultra-high-end GTX 1080Ti, 2080Ti or Vega 7 ... most are only around 200W
- Board and other stuff is at most 50W
- Extra HDDs are 5W/drive, even if you have lots of USB stuff plugged in ... that's no more than extra 20W

Even a 450W good quality PSU can power a gaming PC with ease, especially considering that actual games don't hit those power levels (only synthetic tests/power virus software, like Furmark)

750 is COMPLETE OVERKILL for anything other than extreme overclocking/record breaking stuff.

Oh, and SLI/Crossfire is dead... that was the only good reason for having PSU's above 600W

 

[Turmania]

So does that mean we can use only 8 pin even though MB has 8+4 slot? For instance i9 9900k with stock speeds and system will work?

 

[HUSKIE]

Even just one 4 pin will power the Cpu up.

 

[Wavetrex]

Yes.
(to both posts above)

9900k I wouldn't try with just one, that thing can draw some amps...
But it certainly can with the full 8-pin (4+4).

See same question being asked in the past.

Motherboard with 8 Pin + 4 Pin CPU Power - But you only have an 8 Pin, what do you do?

I was curious, motherboards like the Asus X99 Sabertooth have both an 8 pin and a 4 pin power plug for the CPU. However, what should you do if your power supply only provides one plug for the CPU (an 8 Pin)? For example, I was thinking of picking up the...

forums.tomshardware.com

Even the horribly inefficient Haswell-E and Broadwell-E from that time, that sucked up easily 200W by themselves, can be powered with just 8-pin.


@OP
Be happy you have an extreme overclocker board, in case you suddenly develop the desire to pour Liquid Nitrogen on your CPU

p.s.
A read on ATX specifications, if you're really REALLY bored ... https://en.wikipedia.org/wiki/ATX
"8 amperes maximum per pin", that's 32 Amps x 12 v = 384 Watts max coming through that 8-pin. You won't reach that without LN2

 

[schrstopph]

I had same problem. I got an adapter to use extra pcie power. Don't listen to the power police about not needing to use the extra 4 pin. I was unable to get my ryzen 5 3600 up to 4.2 until I connected mine. And I am far from an extreme over clocker. So, I call bullshit on those replies.

 

[EzioAs]

I had same problem. I got an adapter to use extra pcie power. Don't listen to the power police about not needing to use the extra 4 pin. I was unable to get my ryzen 5 3600 up to 4.2 until I connected mine. And I am far from an extreme over clocker. So, I call bullshit on those replies.

Dude, 8-pin is wayyy more than enough for any CPU without extreme overclocking as the others have said. Maybe you plugged yours wrongly so you assumed you had to use the extra 4-pin to power your system or it could be some other issues specific to your case, but don't go spouting nonsense and call other BS or something without any definitive reasoning. In fact, I guarantee OP can check all those motherboard's manual and they'll probably say users don't need to plug in the extra 4-pin unless in extreme circumstances.

EDIT: now I just realized that above post and mine have bumped this thread unnecessarily. I apologize.

 

[cjw13cjw]

I had same problem. I got an adapter to use extra pcie power. Don't listen to the power police about not needing to use the extra 4 pin. I was unable to get my ryzen 5 3600 up to 4.2 until I connected mine. And I am far from an extreme over clocker. So, I call bullshit on those replies.

unsure why you would have this problem, I’m currently over clocking a Ryzen 7 3700x to about 4.3 with no issues on a CX750 PSU just using 8 pin