[SOLVED] 8+4 pin 12V CPU power on mobo, I only plugged in 4 pin from PSU. Did I goof?

[MCMailbox]

Hi all,

So on this PC I built early last year, the motherboard (Gigabyte Z390 Gaming X) has both an 8 pin and 4 pin 12V connector for the CPU, common in Z390 motherboards. However, my PSU (EVGA 650 G3) only has a 4+4 pin 12V CPU lead, so following some advice I found online...

https://linustechtips.com/main/topic/1010779-gigabyte-z390-elite-power-connectors-question/

...I only plugged in one 4 pin from the 4+4 on the PSU to the 4 pin on the motherboard, leaving the 8 pin on the motherboard empty and tucking the other 4 pin from the PSU behind the motherboard shroud. Today, I read that you're supposed to use AT LEAST the 8 pin with the 4+4 on the PSU and leave the extra 4 pin on the motherboard empty unless you plan on doing some extreme overclocking...

https://linustechtips.com/main/topic/980995-z390-boards-84-pin-atx/

Astonishingly, I was able to OC my i7-8700k to 5GHz at 1.34v no problem, stress tested with p95 and everything, totally stable. But if this is a disaster waiting to happen having only the 4 pin plugged in then I want to change that ASAP.

So I wanted to see what the final word on this issue is. Am I good to leave just the 4 pin connected with the 8 pin empty as is, or should I switch to 8 pin connected with the 4+4 and leave the 4 pin empty?

Thanks!

Full specs:
Gigabyte Z390 Gaming X
i7-8700k @ 5GHz 1.34v
Corsair H100i (old version)
Vengeance RGB 2x8gb 3200c16
AORUS GTX 1080ti
EVGA 650 G3

 

[Barty1884]

I don't think it's an outright disaster waiting to happen, but I'd run the 4+4 EPS.

I don't remember the exact specifics, but the rated power draw for EPS is something like 150W for 4pin and 250W for 4+4 ie 8pin. Don't quote me on those numbers exactly, but it gives you an idea.

Even if it does work, it doesn't mean it's sustainable as is. The gauge of the wiring is only rated to supply X.... I'd be stunned is a single 4pin could reliably power an 8700K with a good overclock on it for the long-run.

Better safe than sorry, use 4+4.

 

[Landstander]

I spoke with an ASUS rep about a similar situation. He claims that although 8 is enough to run, 8+4 will prevent the board from being underpowered... and that an adapter to supply the missing connector is fine.

What I'm probably going to do, and you could as well, is use your 4+4 connector on the 8-pin socket and then get a molex to 4-pin adapter.

 

[Barty1884]

I spoke with an ASUS rep about a similar situation. He claims that although 8 is enough to run 8+4 will prevent the board from being underpowered

That is just complete garbage, honestly. An i7-8700K is a 95W chip, and a 4+4EPS can provide up to 236W.
Unless you're using exotic cooling, the additional 4 pins is a complete waste - you can't (near) 3x the power draw of an 8700K with any form of 'normal' voltage & cooler.

The ASUS rep, I'm assuming was via email or live chat functionality. They are not involved in the design of the product, nor are they necessarily particularly knowledgeable. It's like any customer service job, and (generally_ operating from a a script.

IF they knew what they were talking about, they'd tell you that if you wanted to use the extra 4pin for peace of mind, you should utilize a PSU that has multiple EPS cables for this very use-case.

While in theory, Molex to EPS is fine (both are just 12V + Ground), you can run into concerns between the amperage & the gauge of wires used when drawing off molex.
IIRC, depending on the PSU, Molex cables will use gauge wiring sufficient for between 6-10Amps (72-120W), whereas an EPS connector, even 4pin, can provide up to 150W.
Not to mention, el-cheapo adapters are likely to have cut corners too, meaning the adapter itself could be of lesser gauge wiring still. In theory, you could draw ~150W through a connector that's rated for (at best) ~120W AND an adapter that's likely designed/rated for even less.

Drawing additional Amps through a cable of too thin gauge is just asking for trouble, even if it's highly unlikely to ever be utilized -- and no 'rep' should ever be recommending use, for those reasons.

 

[Landstander]

The board I was asking ASUS about was a TUF GAMING X570 PLUS, so its power demands ARE higher.
You can get dual molex to 8-pin and single molex to 4-pin cables.

I agree with you. From what I was reading, it looks like molex is rated at half of what a 4-pin ATX cable can carry.

The numbers don't jive, but people still make the cables (even respectable companies like Monoprice), but if your CPU starts drawing more than 400w, let alone 500+w, you've got worse problems.

Still, I'm surprised no one makes a PCIe power to 4-pin, since it's capable of carrying a heavier load.

Edit: Come to that, it would make sense to build a dual molex to single 4-pin ATX. Which I'm now thinking of doing myself.

 

[Barty1884]

The power demands are not higher on that board, at least not today. In theory they are, but the most power hungry chip they can support today (3950X) is a 105W TDP, and accurately draws <160W until 100% load. There's minimal overclocking headroom. Feasibly, a highly overclocked 8700K could better it in terms of power consumption.

I suspect AM4 board vendors/AMD themselves are including more supplementary EPS connectors on 500 series motherboards, as they're maintaining socket support for at least one more round of chips..... a decent bump in power consumption might be required. That's just speculation on my part though.

As for Molex to EPS.... yes, adapters exist. Known brands with a reputation to protect (MonoPrice, StarTech etc) are probably fine. Nobody will ever officially recommend though - as there shouldn't be a need to recommend based on brand, and accusations of collusion would likely come up.

In order for it to be standard practice, it has to mostly be "get X" regardless of brand etc, which is risky.
A Monoprice Molex to EPS is almost certainly spec'd for the power draw in terms of wire gauge. No-name $2 item "first from Asia"... potentially not so much. Similar to how Nvidia or AMD state "xyz Watt PSU required". Quality units will get by with anywhere from a little to a lot less, poor quality units will not, but they have to go with a 'safe' number.


As for why no PCIe to 4pin.... it's probably a combination of reasons:
1. 8pin PCIE, as well as 6pin has 3x 12V wires.... it's Ground that changes (3 or 5). So for the 6pin alone (essentially all you'd be adapting), you're back to a ~75W max power draw.

2. Lack of demand (very few boards in the grand scheme of things have the additional 4pin)

3. People without additional EPS connectors (generally <750W PSUs) have a limited number of PCIe connectors vs Molex that (mostly) go unused these days.