Installing a 4090 and a 1200W PSU

Hardware & Tech Questions
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Yesterday I had to go to the inlaws to fix some stuff and the new GPU had to wait…
Today, I started by updating the Motherboard BIOS, as some Varjo VR users have been having issues on ASUS Motherboards with old BIOS and a 4090.

I removed the 3090 with the entire cooling loop.

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The 4090 has three fans and a cooling pipe arrangement.
It is huge!

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This is the infamous power connector that reduces 3 PCI power cords to this little thing… A theory about the meltdowns is that the connector isn’t fully seated. This one has a latch and can’t come loose by itself. Let’s hope it’s one of the good cable and connectors…!

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It’s a big GPU! It even has an adjustable support, at the back.
But the old setup took up more space, with the liquid cooling loop.

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Powered up and installed the latest drivers, jumped into DCS for a quick test of the same mission I tried before the swap.

Not a single hickup! Sooooo smoooth!
Need to test more scenarios, and up the details, but the 4090 performs noticeably better than the 3090. I expected that, of course, but it’s good to see it with my own eyes.

Now, beer! :beers:

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the deisgn of the connector is the problem,

The little clip to hold it in the connector, is not big enough to handle side to side torque of the big 16-pin connector,

so even if the little clip is clicked in, side to side torque can move the male connector out of the female connector 3-4+ mm on the side pins and from that point you’ll have the arching problem and meltdowns.

When we were testing this connector 4 years ago, we told nVidia and PCI-SIG about it, nothing was done.

As wide as that connector is, the clips should have been places on the left and right sides, not the top center.

Also a 4090 should have 4x 8 Pins to 16-Pin, not 3x.
You’re starving it of power and limiting it to 450w out of the 600w

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When I pull at the cable and bend it, I can’t get the connector to move a fraction of a mm, let alone 3-4…?
Not without unlatching the clip…
But I’ll keep an eye on it.

Then why are there only 3 connectors on the supplied cable? I mean, they could easily have put another connector on there?

Do you have any suggestions?

Edit.
I’m looking at these 90° or 180° adapters from CableMod. They will help taking the stress off the connector. CableMod also have 12VHPWR to PCIe cables, both 3&4 8 pin PCIe connectors.

Their FAQ says this:

DON’T PCI-E PORTS ONLY PROVIDE UP TO 150W PER PORT? HOW IS IT THAT A 3 X 8-PIN (OR 2 X 8-PIN FOR THAT MATTER) CABLE CAN BE SUFFICIENT TO POWER GPUS THAT REQUIRE UP TO 600W AT PEAK?

In truth, an 8-pin PCI-e port on modern PSUs can supply over 300W of power each (up to 342W, depending on model). Thus, two 8-pin PCI-e ports are more than enough to provide the required 600W. We provide both 3 x 8-pin and 4 x 8-pin versions of this cable for extra redundancy.

So, if that’s correct, 3x PCIe power should be more than enough…?

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Def keep an eye on that bending … I see some lateral bending in that last pic.

I’m surprised the 4090 only has 3 8 pin power inputs! Was expecting 4 since my 4080 only has 3 and my new 1200W power supply has 4 outputs.

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Be careful with the bending,

Also per PCI-SIG:
PCIe / ATX v2.0 Power
8 Pin Peak 150w
6 Pin Peak 75w

3x8 Pin = 450w + 75w in the Slot = 525w.

Depending on the Clocks, you may be safe, but afaik, nVidia wanted all 4090s shipped with 4 8 Pin to 16 12VHPWR, as it would balance the load better.

Being a 3x 8 Pin to 16Pin, 3 of those 12 Leads are Disabled as every 8 Pin in the Adapter Closes the circuit for 1 of the 4 Sensor Pins (or is supposed too). if the GPU Doesn’t detect the sensor circuit is closed, it disables 3 of the Input Leads to make sure its only drawing power from a Clean 8 Pin Circuit.

1x 8 Pin goes to 3 of the 12vHPWR Leads (2 Hot 1 Ground), and 1 Lead goes to 1 of the 4 Sensor/Data Pins,
The issue is some Adapters are MFG’D with all of the 8 Pins just cross connected on the 12VHPWR Leads, and the ATX3.0/DATA Pins are just tucked into the sleeve.

So instead of the GPU Monitoring the Power Input and adjusting which leads draw more power, it just does whatever it wants randomly, as soon as you max load the rail with GPU and CPU full load by accident, poof, PSU dies.

As Soon as 1 Rail Dies or starts to drop it’s output it tries to pull more than 150w from the remaining 2 8 Pin connectors and becomes unstable.

With each 8 Pin connected to a correctly mfg’d adapter, the data pin should detect a closed circuit and the GPU should know how many 8 Pins it has, You can run a 4090 that comes with a 4x 8Pin to 12vHPWR on 3 12 Pins, and leave the 4th unplugged, the GPU will (if the adapter is mfg’d correct) sense it only has 450w and limit the power from the 12vHPWR connector.

Their FAQ Response assumes everyone has a PSU that is capable of putting out 300w per connector and it’s simply not the case, they will have issues with that down the road.

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cheers :beers:

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I have been very cautious, as I was aware of the issue.
The cables must bend, of course. I think that the important part is not to introduce any loads on the connector. As I try to pull and wiggle the connector, the whole GPU moves. It does seem like a very solid connector…
From all the coverage this issue has gotten, it seems that the general consensus is faulty cable, poor insertion and/or debris in the connector. About 0.04% failure rate reported, so far.

The PSU I got has a single/multiple 12V rail switch and the manual says:

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So, with the switch in multiple, it will limit the output to 40A (12V x 40A = 480W) per cable. So, that would still mean that two PCIe outputs would be plenty? This would also be in line with how Corsair made their 12VHPWR cable, that has just two 8-pin connectors on the PSU side and a rating of 600W.
That said, if I’m going for a new cable with an angled connector, I could just as well get one with 4 8-pin PSU connectors. The PSU has enough ports. :slight_smile:

I admit that my knowledge in this area is limited and I mostly do what I’m told, from reading articles and listen to people like you, @SkateZilla :slight_smile: Thanks for keeping an eye out for me! It is very much appreciated!

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You should be fine then.

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Until I’m not… :wink:
Don’t give up on me!

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Hey @Troll, out of curiosity, did you replace ALL the old PSU related cables with the ones provided with your new PSU?

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Yes, I did.

Well, apart from the EATX power cable A, in this pic, for which there were no cable either with the old, nor new, PSU. So I used the old one that I bought separately when I built this PC.

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When I went to the computer store to get an extra PCI-E cable for my old PSU, the guy told me never to do that as aftermarket cables might fry my mobo! I found that quite surprising and didn’t want to argue so I just bought a new power supply. Him telling me to always use cables that come with the PSU really stuck with me though and I’m glad you’re doing so. It’s weird that cable A didn’t come with your PSU. All the EATX cables came hard wired with my new PSU. I’m still scratching my head on this though as I’ve only installed cable B (no A) …

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(in the above diagram, your cable C is cable A)

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Yeah, I was not sure what to do about that small socket. Tried to read up on the subject but found nothing conclusive. So I ordered a cable from a reputable manufacturer.

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The EATX 12V, sometimes also called CPU power, is similar to the PCI 12V, or GPU power, in that the number of pins varies with the required power. Except that instead of blocks of 6 or 8 pins, they come in blocks of 4 or 8 pins.
The cables go into the same holes on the PSU side as the PCI 12V cables, at least on my Corsair 850x.

Low-end motherboards often have only 4 EATX 12V pins but high-end motherboards typically have 8 pins. I have only recently seen more than that being used, I think it is because of the incredibly high power consumptiom of the newer high-end Intel CPUs.
IIRC you can safely have an unfilled slot on the mobo, unless your CPU needs that much power.

Elby’s Ryzen (?) CPU is very efficient and doesn’t need more than 130 W, thus there is no use for another set of 4 EATX 12V pins.

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That, plus 4 connectors are not impossible to double check, even for somebody who’s not knee deep into electronics. It‘s two - (black) and two + (red) connectors.

The power supply should come with a pinout of the outlets which can be compared to the EATX pinouts. Just make sure not to confuse male vs. female.

If your power supply did not come with a pinout, that should be a no go anyways. :slight_smile:

It‘s crazy how power consumption on desktop PCs still only knows one direction: Up. Hope they stop that madness.

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Just happen to be starting a new build this past weekend (first one in like 6 years) and am also wondering whether I should plug in the extra 4 pin CPU power to the MB.

Instructions are just like Elby’s, picture indicating you can do the 8 pin ‘or’ do the 8 pin and the 4 pin, but nothing as to why you’d do one versus the other.

Like Troll I haven’t found anything definitive online. Basically seems like most people are saying you don’t need more then the 8 pin unless you are doing crazy (like liquid nitrogen) overclocking, but then occasionally there will be a post from someone who benefited in some way from having plugged in the 4 pin in addition to the 8 (like they weren’t able to even do a mild OC without plugging it in).

I’m leaning towards just plugging it in, as I can’t imagine it would do any harm. Wondering what you guys would/will do?

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I have both the 4 and 8 pins plugged in, but I don’t think both are needed.

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If you have both cables and are easily within total power budget incl GPU, there’s no harm in plugging it in.

Whether it benefits you depends on how much power your CPU will draw.

What is the precise model of your CPU?

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Thanks guys!

It’s an i7-12700k, I have (for the first time ever!) an “80” series card in the 3080 which is pretty exciting, have only been able to afford the ‘70’ or ‘60’ types in prior builds.

Will be oc’ing the cpu but nothing too crazy, the power supply is an evga 850 G5 so I think I’m within the ‘power budget’.

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Yes, should be fine for the 850W PSU.

According to a reputable reviewer I am checking (Tweakers.net, a Dutch site) the 12700K pulls 150 Watts in Cinebench R23. I am not 100% sure but I think that is around the level where it will probably help performance a bit to have that extra power.

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