RTX 4090 cables

[bflo]

I need cables for my new 4090, one has 2 to PS, & another has 4 to PS.   Which should I get ?    Thanks for recomendation.

[razo+r]

How many pins does the GPU have? If 2x8 get that one otherwise get the 4x8.

Also make sure your PS is compatible with the cable. 

[bflo]

Thanks for quick reply, GPU has 12 pins.   I watched a clip & wondered why he chose 2 instead of 4, I have the same card.

 

Edited September 12, 2023 by bflo

[dburne]

4.

[bflo]

Thank you

Edited September 13, 2023 by bflo

[bflo]

Crap,I screwed up, that cable needs a 12 pin to the PS, & the one I have is in use.  Things run alright with the 4 singles I'm using, I just thought I could clean things up little.

[DocSigma]

I use the seasonic 12v for my 4090 and its just one combined cable. Its quite nice.

https://seasonic.com/12vhpwr-cable#


Sent from my iPhone using Tapatalk

[dburne]

On 9/28/2023 at 2:46 PM, DocSigma said:

I use the seasonic 12v for my 4090 and its just one combined cable. Its quite nice.

https://seasonic.com/12vhpwr-cable#


Sent from my iPhone using Tapatalk

 

600 watt cable for a 4090?

[kksnowbear]

3 hours ago, dburne said:

600 watt cable for a 4090?

Yes. It's been documented that 4090s can draw in excess of that (though obviously not continuously). I know of at least one instance where the excursions were measured at 700w, if I recall correctly.  If the cable isn't set up for 600w sideband signaling via the 12VHPWR cable, the GPU will inherently limit what it draws from the PSU.  This behavior is by design, allowing the GPU to "know" how much power the PSU can provide.

Why do you ask?

[dburne]

4 hours ago, kksnowbear said:

Yes. It's been documented that 4090s can draw in excess of that (though obviously not continuously). I know of at least one instance where the excursions were measured at 700w, if I recall correctly.  If the cable isn't set up for 600w sideband signaling via the 12VHPWR cable, the GPU will inherently limit what it draws from the PSU.  This behavior is by design, allowing the GPU to "know" how much power the PSU can provide.

Why do you ask?

 

Just curiosity was up as the 4090's can be a bit power hungry. I believe min. they recommend for PS is 800w.

[Mainstay]

You need to connect all 4 of the cables to let the card be able to peak 600W.

It will run with only 3 connected but then you cap the card to a maximum use of 450W.

[kksnowbear]

On 9/30/2023 at 3:19 AM, dburne said:

Just curiosity was up as the 4090's can be a bit power hungry. I believe min. they recommend for PS is 800w.

The terms "minimum" and "recommended" are, pretty much universally, two different things.  At least according to the specifier, you must have at least the minimum, but you really should have the recommended.

Although I'm admittedly not checking specs right this minute, I believe the 'big three' GPU manufacturers still left in the game in the US since eVGA bailed (i.e. Asus, Gigabyte and MSI) specify an 850W PSU as minimum for some of their 4090 models - but they also recommend a 1000W unit for some of their high-end models.

Of course, some of the 'experts' here have tried to insist 850W is enough, but the actual load is going to depend a lot on the exact PSU and also on the circumstances.

Considering it's proven that a 4090 can draw 700W *by itself* in the right circumstances, plus factoring in the kind of money someone will have spent to have a 4090 in a system in the first place (and the balance of the system's cost as well)...

...I can't imagine why anyone would want to 'cheap out' on a minimal power supply.  Never a good idea TBH.

I have a 4090 myself, and I have measured 650W as a max from the wall - but there are a *lot* of "howevers".  One is that most consumer measuring devices simply are not going to be accurate/sensitive enough to 'catch' the extremes that usually occur faster than most meters can sample.  This applies equally to software, and/or displays driven by software (such as on front of a UPS).

Any professional meter good enough to measure this kind of thing is going to be extremely expensive, and not something any typical consumer would ever own.

Additionally, many people (for various reasons) use the 'tail' that came with their GPU, because their PSU doesn't have a 12VHPWR connector.  Some of these tails are set up to limit what the GPU can draw, by omitting the sideband signalling pins.  But, anyone can buy a 600W adapter cable and slap it on a PSU that cannot deliver that kind of power to the GPU.

Whether the 600W cable makes a significant difference in performance might be arguable...but what *is* clear is that it's stupid easy to 'fool' a GPU into thinking it's OK to draw 600W, even if the PSU isn't up to it.

Finally, there is also the VBIOS.  The GPU's VBIOS will have a certain power limit programmed in it.  Usually, this value is based on actual hardware, because by design it considers components (like voltage regulators) on the card itself.  So a GPU built with VRMs that can only handle 450W will have a corresponding power limit.  Low end units will have lower power limits than high end units, which are typically the only ones you see with 600W power limits in VBIOS.  Thus, even *if* you program a card with VBIOS that has a higher power limit value, you still don't change what the hardware itself is capable of, and you could damn well wind up frying your card (or 'bricking' it altogether) by screwing around with something you shouldn't be.

I see a real potential here for people who don't know what they're doing - because they think it's a "free" GPU performance upgrade - to buy these 600W cables and fit them to a PSU that might not be appropriate to it, and/or with a GPU that is VBIOS limited anyway.  Stupid and dangerous, IMHO (I've already seen one member on this very forum who has done exactly this...there was a thread about it but he got butthurt when I pointed out issues in his results, and he deleted the thread...lol which of course doesn't change the facts).

On 10/2/2023 at 10:42 AM, Mainstay said:

You need to connect all 4 of the cables to let the card be able to peak 600W.

It will run with only 3 connected but then you cap the card to a maximum use of 450W.

Actually, that depends on how the cable is made.  You can create a cable that will 'tell' the GPU that it can draw 600W, regardless of the actual PSU and cable...it could be a hardwired SATA power cable on a 400W  PSU and it can be 'fooled' by a specifically constructed adapter/cable.

I AM NOT RECOMMENDING ANYONE SHOULD DO THAT - EVER - But the reality is that it's entirely possible.  Of course it won't work very well, if at all...and this is what's wrong with people just buying these connectors/adapters without understanding the other factors involved.

As usual, just because someone sells something that will connect two otherwise incompatible devices doesn't mean it's going to work (and possibly, spectacularly so).  Whether you attribute it to George Carlin or WC Fields, there's a saying: “If you nail two things together that have never been nailed together before, some schmuck will buy it from you.”

Hardware makers - especially cable manufacturers, it seems - are constantly 'nailing two things together' and uninformed or misguided people will line up to buy them.  Factually, just because you can plug this into that doesn't mean it's going to work, nor that it was ever intended to be connected that way.  And again, you can damage stuff doing this.

Anyhow, as always, the foregoing is strictly my opinion - which is typically based on verifiable fact

Edited October 5, 2023 by kksnowbear

[dburne]

Yeah I am running a 1000w with my 4090 and glad I have it, certainly have had zero issues at all.

[kksnowbear]

28 minutes ago, dburne said:

Yeah I am running a 1000w with my 4090 and glad I have it, certainly have had zero issues at all.

If I'm looking at it correctly, yours is one of the aforementioned GPUs for which the manufacturer recommends a 1000W PSU (the "Gaming OC" model?).

It appears that model uses a VBIOS that supports a 600W power limit.  If (whatever cable arrangement you use) supports 600W sideband signalling, and/or you have a PCIe 5.0-compliant PSU with a 12VHPWR connector, you should be all set.

The lesser Windforce model has a PSU recommendation of 850, and accordingly, appears to have a 479w power limit in VBIOS (or possibly 500W, not 100% certain and don't have one to test).  This is almost certainly because of lower spec hardware (VRMs) used on that model.

Again, whether the 'extra' power allowed for in the 600W cables increases performance at all is not at all certain (and definitely not at all if the limit is lower in VBIOS, regardless of cable or PSU).

Edited October 2, 2023 by kksnowbear

[Richi]

It's interesting how people save money on components that should come first.

GPU is only expensive but not important, PSU is important.

I bought a FSP ATX3.0(PCIe5.0) 1200W for my GIGABYTE GeForce RTX 4090 GAMING OC 24G. Maybe 1200W is too much, but the power reserve doesn't hurt anything.

Edited October 3, 2023 by Richi

[kksnowbear]

Well...I might not consider the GPU unimportant lol but I think I see your point.  PSU is definitely important.

1200W isn't necessarily too much, really...there is a legitimate argument that running the PSU at 50% load is most efficient (therefore less power used and less heat generated).  If a 4090-based system runs ~650w, then a 1200w PSU puts you right around 50% load when gaming.

The exception is when you're *not* gaming; the power supply is hardly loaded at all and efficiency drops...but not much you can do about that and it's a different discussion anyhow.

The only 'problem' there might be with a top-end very high wattage PSU is cost.  But, as discussed above, if you spend the kind of money to have a 4090 in the first place, then a more expensive PSU isn't outrageous.  It doesn't makes sense to 'cheap out' on a PSU to save $50 when the balance of the system exceeds $2000