Effect of 20pin mobo and 4pin cpu power only

[K1ng]

Just curious and cant find any where that test the actual effects of running a motherboard designed for 20+4 pin power and 8pin cpu power on just a 20pin psu and 4 pin cpu psu.
I know it works fine even on up to a ryzen 2200g it may work on better cpu and setups but i have not tested that. But what i am unsure on is the actual over all performance difference if any. And if there is and it is dependent on system load at what point does it matter and is it even motherboard dependent? I know cpu overclocking can be cut short by not powering the cpu but im talking just straight plug and play performance no tweaks.

Would be a interested Tech Quickie but not sure it could hold up for an entire dedicated video unless you did a gauntlet of mobo and psu and cpu testing.

[Stormseeker9]

They’ve been designed that like for a reason I assume

[K1ng]

? Im just asking what the over all effects are if they have been tested? Like take a cpu and bench it with a full 24pin and 8pin power for mobo and cpu and test it with a 20pin and 4pin psu. For say an average user who is not overclocking would there be any disadvantages?

[Guest]

You'll just burn up the PSU connector if you draw too much power. 

[K1ng]

2 minutes ago, jonnyGURU said:

You'll just burn up the PSU connector if you draw too much power. 

But will it draw more power? Will the motherboard tell its only a 20pin and a 4 pin and limit its consumption?

[mariushm]

No effects dude.

 

The 4 pin connector on a 24 pin connector simply add one extra wire for each voltage: 3.3v , 5v and 12v. The fourth wire is ground.

 

In the 20 pin connector, there's 4 x 5v wires and 3 x 3.3v wires, and on modern motherboards that's more than enough, modern motherboards probably consume around 30-40 watts on 3.3v and 5v combined, and the motherboard can receive up to around 90 watts on 3.3v and around 135w on 5v so there's plenty of room.

 

The problem is the 12v part. The ATX connectors were designed decades ago when motherboards used mostly 5v, so the 20 pin part has only ONE 12v wire, which means it can receive only around 110w safely through each 12v wire.

If you insert the 4pin part, the motherboard can take 12v energy from two wires instead of just one, raising the top limit to around 220 watts.

The 12v on the motherboard is used to power the fans (around 1-2w each) and it's also used to power pci-e slots: each video card in the computer can take up to approx. 65w of power from 12v.

So, if you have a decent video card, the video card alone and the fans in your computer will take up to around 80-90w out of the maximum safe limit of 110 watts.

If the power supply is a cheap one, if the connectors are flimsy, if the wires are thin, at such high levels of continuous load it's possible for the 20pin ATX connector to become brittle or loose due to connector being warm or even hot all the time.

 

If you're using just the integrated graphics inside the CPU, it's not that big of a deal - the integrated video card is powered from the CPU connector, not the 20pin/24pin connector.

 

As for the CPU connector, well you have 2 pairs of 12v wires, and each pair can give up to 9A of current to the CPU. This means the dc-dc converter which powers the processor can safely take up to 2 pairs x 9A x 12v = 216 watts of energy.

The dc-dc converter will be up to around 95% efficient in converting the 12v to the small voltages the CPU needs, so assume there's more than 200 watts available to power a CPU.

 

A 200ge processor (dual core Ryzen) will consume up to around 45 watts. The 2200ge will consume maybe up to 80 watts or so. A cpu like Ryzen 2600 will probably consume up to around 110-120 watts

 

So a 2200g will work just fine with 4 pin connector, and lots of modern processors will work perfectly fine as they don't get close to 200 watts of power consumption.

 

You have to concern yourself with the QUALITY of the power supply - the fact that the psu comes only with a 4pin cpu connector, or that the 24pin can be split in two, may be a sign that the psu is an old design or a very cheap one that may not last a long time.

[K1ng]

Ok that was a great and helpful answer mariushm. I was sure it was (for the most part safe) as i have done this for many years on cheap janky fun builds. And my sons 2200g has been running just fine with to me no noticeable performance loss with a 255w dell oem psu(not sure what manufacturer i was just sure 250w was plenty for a 2200g with one m.2 keyboard, mouse, and gamepad and maybe ocassional other peripherals.

I was tempted to try a 2600 or 3600x but then it would of been alot of work especially without the time or equipment to properly check and the time to run ALL the benchmarks. 
So essentially kinda like my assumption if you do not overload the wattage of the psu and the psu is not poorly made everything will function just fine.
And on newer psu i would assume that if you did over draw power the psu would probably just shut off before any damage is done if it is detectable like over temperature in likely areas of failure. (and this is if you can find a even marginally quality psu made in 2019 with just a 20pin mobo and 4pin cpu) 

[Guest]

57 minutes ago, K1ng said:

But will it draw more power? Will the motherboard tell its only a 20pin and a 4 pin and limit its consumption?

It will draw the same amount of power... just with less conductors (wires).  This increases the current across individual wires, increasing resistance and reducing voltage.