Corsair RM850x and NVIDIA 4080 16GB, Be Prepared to order another Type 4 PCIe cable Grrr!

[John1272]

So, I was almost done with the hardware part of my build and then I realized the Corsair RM850x came with 3 EPS cables WTF WHO NEEDS 3 EPS CABLES!!!! and not 3 PCIe cables.  Read lots of theories as to why there are not 3 PCIe cables in the box but none makes any sense so we will just say someone screwed up and leave it at that.

 

If you do find yourself with a Corsair RMx series PSU and a 40series card needing 3 PCIe cables DO NOT be tempted to plug in an EPS cable into the adapter that would likely smoke your GPU.   You will want to order this Type 4 cable part number directly from Corsair CP-8920143 for $3.99 which has the inline Caps used to reduce ripple which in turn reduces heat in, and prolongs the life of, your GPU hardware.  YOU COULD ALSO BUT I WOULD NOT order any of the Type 4 Gen 4 PCIe paracord cables for $20 BE WARNED those cables do not have the inline Caps used to reduce ripple, they are pretty, but this is a case where more expensive does not equate to a better product.

 

Type 4 Sleeved black PCIe cable with pigtail connector and capacitors for Type 4 PSU (corsair.com)

[PDifolco]

Can't you do with the 2 cable using both connectors of one of them ? That's 300W+ power and the RM850x will certainly have no issue with 400W..

I have this PSU, and for some time my 320W RTX3080 was connected with just one 2 headed cable and worked perfectly ... I added the second one with all the fuss about power spikes eventually  

 

[John1272]

7 minutes ago, PDifolco said:

Can't you do with the 2 cable using both connectors of one of them ? That's 300W+ power and the RM850x will certainly have no issue with 400W..

I have this PSU, and for some time my 320W RTX3080 was connected with just one 2 headed cable and worked perfectly ... I added the second one with all the fuss about power spikes eventually  

 

You could risk it if your 40x series pulled less then 300W at peak I suppose.  The 40x series I have is the 16GB version so it pulls 320W at peak each of the Type 4 PCIe cable is only rated for 150w so I would be risking blown caps or melted cables if I only used 2 cables.  To that end NVIDIA says to use three cables not two and I can't afford to buy another 4080 GPU - $1200 vs $3.99+shipping I think you get my point.

[jaslion]

Just connect both of the 6+2 pin connectors on the cable?

 

Its fine sure not as good as individual cables but totally fine to do.

[John1272]

2 minutes ago, jaslion said:

Just connect both of the 6+2 pin connectors on the cable?

 

Its fine sure not as good as individual cables but totally fine to do.

No its generally not a good idea to run a cable over its peak rating, that's how things melt.

[PDifolco]

1 minute ago, John1272 said:

You could risk it if your 40x series pulled less then 300W at peak I suppose.  The 40x series I have is the 16GB version so it pulls 320W at peak each of the Type 4 PCIe cable is only rated for 150w so I would be risking blown caps or melted cables if I only used 2 cables.  To that end NVIDIA says to use three cables not two and a can't I afford to buy another 4080 GPU - $1200 vs $3.99+shipping I think you get my point.

Don't think you risk anything : 2 PCie cables give 300W but then the PCie slot also gives 75W, plus the PSU can stand much more, and the extra load of max 50W won't  meld cables or anything

 

[John1272]

1 minute ago, PDifolco said:

Don't think you risk anything : 2 PCie cables give 300W but then the PCie slot also gives 75W, plus the PSU can stand much more, and the extra load of max 50W won't  meld cables or anything

 

It's your money you can do whatever you want I just wouldn't recommend it.

[jaslion]

48 minutes ago, John1272 said:

No its generally not a good idea to run a cable over its peak rating, that's how things melt.

The cables are rated for like 600w each dont worry shit wont melt

[John1272]

17 minutes ago, jaslion said:

The cables are rated for like 600w each dont worry shit wont melt

Ya that's not true.

[jaslion]

3 hours ago, John1272 said:

Ya that's not true.

It is 18awg wire which is perfectly fine for 9.5 amps at 12v will do 114 watts a wire

 

So do the math and cpunt each wire togheter and well done

[John1272]

25 minutes ago, jaslion said:

It is 18awg wire which is perfectly fine for 9.5 amps at 12v will do 114 watts a wire

 

So do the math and cpunt each wire togheter and well done

I wish it were that simple, unfortunately it isn't you are forgetting about terminations and the PSU's OCP.  But hey if you want your $1200 dollar GPU to run like crap, pop your wire caps, or melt your connectors more power to ya.

[jaslion]

Just now, John1272 said:

I wish it were that simple, unfortunately it isn't you are forgetting about terminations and the PSU's OCP.  But hey if you want your $1200 dollar GPU to run like crap, pop your wire caps, or melt your connectors more power to ya.

You can run a rtx 3090 on 2 cables on a rmx850 there is nothing to worry here

[John1272]

8 minutes ago, jaslion said:

You can run a rtx 3090 on 2 cables on a rmx850 there is nothing to worry here

I don't have an RTX3090 I have RTX4080 FE 16GB it requires 3 separate cables.  There are also plenty of posts noting piss poor performance, stability issues, and even problems booting when using only 2 PCIe cables on the 4080.

[John1272]

42 minutes ago, jaslion said:

You can run a rtx 3090 on 2 cables on a rmx850 there is nothing to worry here

Think of it like this, my very expensive non E85 sports car will run on E85 so I can save a few cents at the pump, at least it will run for a little while, and while it is using E85 it will run like crap until eventually it just stops working.  So, I think my $3.99 for an additional cable is a good investment.

[Blai5e]

@John1272 - Instead of ordering a Type 4 PCIE cable from Corsair, why not order the Corsair 12VHPWR cable (part number CP-8920284) and be done with the NVIDIA adaptor issue completely?

[John1272]

42 minutes ago, Blai5e said:

@John1272 - Instead of ordering a Type 4 PCIE cable from Corsair, why not order the Corsair 12VHPWR cable (part number CP-8920284) and be done with the NVIDIA adaptor issue completely?

It has no inline caps so you're going to get ripple and thus more heat and wear on the GPU capacitors.  The RM850x uses inline caps on the 12v rail cables, I have no idea how bad the ripple would be if you used a 12v cable without inline caps on an RM850x.  Also, the Cosair chart doesn't show which PSUs this cable is compatible with, I find that kind a sketchy, I personally wouldn't recommend using it with the RM850x in conjunction with a $1200 RTX4080 but it's your call if you do so.  Besides it costs $20plus shipping and the additional PCIe cable only costs $3.99 and it has the inline caps used to reduce ripple with the RM850x 12v rail.

[mr cheese]

My 3060ti pulls 220W through one cable and the PCIe slot.

No fires to date, and that's on a card that used to be at 100% full power draw constantly.

Trust us when we say it works... or just buy the 12V LOL

 

also to be fair you're using an 850W PSU for a 4080 and whatever else, expecting it to come with more cables is only the fault of your expectations

[John1272]

1 hour ago, mr cheese said:

My 3060ti pulls 220W through one cable and the PCIe slot.

No fires to date, and that's on a card that used to be at 100% full power draw constantly.

Trust us when we say it works... or just buy the 12V LOL

 

also to be fair you're using an 850W PSU for a 4080 and whatever else, expecting it to come with more cables is only the fault of your expectations

Didn't think there would be 2 PCIe cables in the box thought there would be 4, read 4 PCIe but it is now obvious they meant 2 with 2 more daisy chained ya that's my fault for not looking at the pictures of the cables on the box.  But NO it isn't a good idea to run it on only 2 cables, for all the reasons I mentioned before and others like voltage drop on the daisy chained connector.  Cutting corners like that just leads to other problems such as stability and heat.

[John1272]

1 hour ago, mr cheese said:

buy the 12V LOL

I am not the type to buy a generic cable for their 4080 just because they want their build to look super clean with minimal cables and I won't buy that particular cable for the reasons I mentioned before, I value peak stability and performance over looks, to me a chocolate coated turd is still just a turd.

[Blai5e]

6 hours ago, John1272 said:

It has no inline caps so you're going to get ripple and thus more heat and wear on the GPU capacitors.  The RM850x uses inline caps on the 12v rail cables, I have no idea how bad the ripple would be if you used a 12v cable without inline caps on an RM850x.  Also, the Cosair chart doesn't show which PSUs this cable is compatible with, I find that kind a sketchy, I personally wouldn't recommend using it with the RM850x in conjunction with a $1200 RTX4080 but it's your call if you do so.  Besides it costs $20plus shipping and the additional PCIe cable only costs $3.99 and it has the inline caps used to reduce ripple with the RM850x 12v rail.

Any Corsair PSU that uses a TYPE 4 PCIE cable is compatible. And before you ask, Corsair has specified that this cable is capable of delivering 600W via the dual PSU-side connections so the Founders RTX 4080 maximum of 450W (directly from the PSU) is well within specification.

 

As for the capacitors... I have a water-cooled EVGA 3090 FTW3 Ultra (bought within 1 week of launch) with the 500W VBIOS using 3 x CableMod Corsair TYPE 4 PCIE 8-pin Pro-series cables which don't have inline capacitors connected to a HX1200i that has presented zero issues. Additionally, my main machine has a water-cooled ASUS TUF 4090 OC (again, bought near launch) that has a 600W VBIOS using the CableMod 12VHPWR to 4 x PCIE Corsair TYPE 4 Pro-series cable (again, no inline capacitors) connected to an AX1200i without any issues.

[Mick Naughty]

8 hours ago, John1272 said:

Think of it like this, my very expensive non E85 sports car will run on E85 so I can save a few cents at the pump, at least it will run for a little while, and while it is using E85 it will run like crap until eventually it just stops working.  So, I think my $3.99 for an additional cable is a good investment.

e85 isnt about saving money. Its about lower egt's and a lower flash point. Wont run like crap if you tune or it already has a content sensor. 
 

[mr cheese]

3 hours ago, John1272 said:

Didn't think there would be 2 PCIe cables in the box thought there would be 4, read 4 PCIe but it is now obvious they meant 2 with 2 more daisy chained ya that's my fault for not looking at the pictures of the cables on the box.  But NO it isn't a good idea to run it on only 2 cables, for all the reasons I mentioned before and others like voltage drop on the daisy chained connector.  Cutting corners like that just leads to other problems such as stability and heat.

It is a fine idea, you don't have to believe us but it's the truth. I run 2 8 pins chained off one cable. Tell me how in 2 years it hasn't caught on fire, despite being overclocked, overvolted, and pulling the max power that a non-stock BIOS would allow.

That said, your money to spend, and your sanity to value. But don't accuse the manufacturer of selling you short for giving you a product that can and will support the power requirements of that card with literally no sweat. If you can't reason through the gauge of cable and manufacturer testing despite an electrical engineer (jaslion) and 2 other people telling you it'll work just fine and is in fact designed to do that, that's on you, not Corsair nor anyone else.

[John1272]

On 3/3/2023 at 10:58 PM, mr cheese said:

It is a fine idea, you don't have to believe us but it's the truth. I run 2 8 pins chained off one cable. Tell me how in 2 years it hasn't caught on fire, despite being overclocked, overvolted, and pulling the max power that a non-stock BIOS would allow.

That said, your money to spend, and your sanity to value. But don't accuse the manufacturer of selling you short for giving you a product that can and will support the power requirements of that card with literally no sweat. If you can't reason through the gauge of cable and manufacturer testing despite an electrical engineer (jaslion) and 2 other people telling you it'll work just fine and is in fact designed to do that, that's on you, not Corsair nor anyone else.

I'm not doubting that you can get it to run daisy chained but there is going to be trade-off for cutting corners.  I will ALSO blame Corsair, nobody needs 3 EPS cables that's going to buy an RM850x, but they could need 3 PCI-E cables.  The only way I would buy the corsair  12HVPWR cable without the inline capacitors which also only uses two of the 8 pinout modular ports is if one of the expert PSU reviewers put the cable to the test with an RM850x on a 4080 or 4090 and proved with actual instrument data it was providing clean power without any performance degradation, excessive ripple, our creating hot spots on the GPU or PSU which can reduce the stability and lifespan of the GPU or PSU.  Barring that kind of review testing I will buy a $3.99 cable and follow Nvidia's recommendations on the two approved power configuration options. 

[John1272]

On 3/3/2023 at 8:41 PM, Blai5e said:

HX1200i

Probably not a good comparison, you could play games and plug in your hairdryer into that thing at the same time without any problems.  I also think the HX1200i has 2 separate 12V rails were as I only have 1 in the RM850x, so I have to plug my hairdryer directly into the wall.   Also, completely different classes of PSUs, the HX1200i is an 80 Platinum where the RM850x is 80 Gold, that's a big deal when you're pushing the PSU into its upper load limits.  It's like comparing a Toyota Camry to a Bugatti.  Oh, and the HX1200i doesn't use inline caps on its 12V rail cables to reduce ripple so inline caps shouldn't concern you at all, the PSU hardware itself does all the work.