Question Corsair CX550, Not Enough PCIe Power Connectors

[fruko]

Greetings all.

My new PSU (Corsair CX550 Bronze, supplies 549.6 watts, 45.8 amps on the 12-volt rail) doesn't have enough power cables (it has two 6+2-pin connectors on two separate cables for PCIe and one separate 8-pin for CPU) for my EVGA RTX 3080 FTW ULTRA, which has three 8-pin connectors.

My other PSU—FSP Hydro (K) 600W, which supplies 552 watts and 46 amps on the 12-volt rail—has more than enough cables (it has two cables, each with two 6+2-pin connectors, excluding CPU cables). I need to swap my old PSU with the new one since the old one is 5 years old. My old PSU supplies my GPU with no problems, no fires so far 😅. (The GPU is undervolted to ~0.86 volts from ~1.2 volts.)

I'm guessing most of you will say that I should use a higher power-PSU, but nope, either I will change the current one with the new one, or I will keep using the old one. Just tell me if I can use the new one with the 3080 safely.

I'm using the GPU with a Ryzen 5 3600, a 512 GB M.2 SSD, a SATA SSD, a 2 TB HDD, and a 4 TB HDD. All HDDs are 7200 RPM.

Corsair's images:

https://imgur.com/dYtovsx

View: https://imgur.com/dYtovsx

https://imgur.com/flQGeBG

View: https://imgur.com/flQGeBG

https://imgur.com/AW9orB7

View: https://imgur.com/AW9orB7

https://imgur.com/iWQLSV9

View: https://imgur.com/iWQLSV9


FSP's specs:

https://imgur.com/rjnP75A

View: https://imgur.com/rjnP75A

 

[Lutfij]

my EVGA RTX 3080 FTW ULTRA, which has three 8-pin connectors.
Due to high transient loads, none of the above PSU's qualify for pairing with your RTX 3080. You're advised to look into an 850W(or higher, ~1KW) reliably built PSU.

My new PSU (Corsair CX550 Bronze, supplies 549.6 watts, 45.8 amps on the 12-volt rail) doesn't have enough power cables (it has two 6+2-pin connectors on two separate cables for PCIe and one separate 8-pin for CPU) for my EVGA RTX 3080 FTW ULTRA, which has three 8-pin connectors.
Thumb rule with PSU's, if your PSU lacks the necessary connectors for your devices, you either have;
a| the wrong PSU for the job
or
b| the wrong components for your PSU.

no fires so far 😅.
If you're going to use adapters to make ends meet for your GPU, then you might want to look through the www of how fires are mostly generated from adapters and yes they can burn down your house.

I'm guessing most of you will say that I should use a higher power-PSU, but nope, either I will change the current one with the new one, or I will keep using the old one. Just tell me if I can use the new one with the 3080 safely.
Looks like you have money to flush down the drain, in that case go with either unit but you should look at yourself(and only yourself) when the GPU and/or PSU(and/or the rest of your system) ends up damaged.

Might want to look through this;

View: https://www.youtube.com/watch?v=wnRyyCsuHFQ

 

[Eximo]

Undervolting the GPU is one way to do it, though a power limit would be safer. As long as you make sure that it is not trying to draw 320W under load, things should be good.

Nothing wrong with a 5 year old PSU necessarily, though getting another PSU with a short warranty isn't exactly wise.

 

[punkncat]

I would actually be surprised if you told me that system would power up on a 3080 with a CX550. As Lutfij is trying to impart to you, this is a GOOD way to damage hardware and waste a lot of money. Neither of your current power supplies are appropriate or safe.

 

[Math Geek]

The equivalent question you are asking is along the lines of, " I bought a $400,000 Lambo and installed an old Ford pinto 4 cyl engine. Why does it not work like a lambo is supposed to?"

The PSU is literally the engine of the system. You went high end with the chassis and bling, but wonder why the crappy engine won't do its job.

That PSU has a place in the world but just not in the world you built for yourself. Do yourself a favor and get the right part for the job

Adapters can make a connection look like a different one, but it won't create more power, which is what you actually need.

 

[fruko]

Thank you all for the time, replies, and advice.

Okay, I'm not gonna use the Corsair with the 3080. I am also gonna power limit the GPU. (I don't have the time or the money to change the PSUs right now.)

 

[Misgar]

my EVGA RTX 3080 FTW ULTRA, which has three 8-pin connectors.

If you've got the 3080 FTW3 reviewed here, your GPU might pull up to 380W (default):
https://www.techpowerup.com/review/evga-geforce-rtx-3080-ftw3-ultra/30.html

With a 5% overclock, which I'm sure you won't use, it could pull up to 400W.

I am also gonna power limit the GPU.

Make sure you dial in a really low power limit. Corsair PSUs are usually pretty good at generating full rated power, but I've got two CX550's myself (in old PCs without PCIe GPUs) and I really don't like the horribly flimsy, light-weight feel of these 550W PSUs. They really are built down to a price.

In comparison, my RM650X is much heavier with more output leads and the RM750X/RM850X are better still. I wouldn't feel happy running an RTX 3080 on anything less than a 750W PSU.

Just tell me if I can use the new one with the 3080 safely.

It depends what you mean by "safely". With a significant GPU power limit, you'll reduce the overload risk on the CX550, but as @Lutfij said, if there aren't enough PSU leads for the GPU, you're using the wrong PSU.

How do you propose to bodge a third 8-pin PCIe output from the two existing cables? Will your GTX 3080 start up with only two 8-pin cables connected or do you need all three power inputs?

Are you perhaps considering one of these 1-to-2 adapters?
https://www.amazon.com/Express-Adapter-Graphics-splitter-TeamProfitcom/dp/B0796NVNY7

It's alright, you'll only be pulling up to 300W from an 8-pin CX550 lead rated at 150W. What could possibly go wrong if you "limit" the GPU power? You might only overload the 150W CX550 cable with 200W instead of 300W.

You probably won't notice any melted plastic due to overheating wires and contacts, unless the magic smoke appears.

Just remember what happens to some 600W 12VHPWR connectors when they get too hot. Are you prepared for a fire? Best of luck.

 

[--SID--]

Which CX550 do you have? CP-9020121 or CP-9020277? It really does matter because one of the two is a trash group regulated unit.

 

[fruko]

If you've got the 3080 FTW3 reviewed here, your GPU might pull up to 380W (default):
https://www.techpowerup.com/review/evga-geforce-rtx-3080-ftw3-ultra/30.html

With a 5% overclock, which I'm sure you won't use, it could pull up to 400W.

Make sure you dial in a really low power limit. Corsair PSUs are usually pretty good at generating full rated power, but I've got two CX550's myself (in old PCs without PCIe GPUs) and I really don't like the horribly flimsy, light-weight feel of these 550W PSUs. They really are built down to a price.

In comparison, my RM650X is much heavier with more output leads and the RM750X/RM850X are better still. I wouldn't feel happy running an RTX 3080 on anything less than a 750W PSU.


It depends what you mean by "safely". With a significant GPU power limit, you'll reduce the overload risk on the CX550, but as @Lutfij said, if there aren't enough PSU leads for the GPU, you're using the wrong PSU.

How do you propose to bodge a third 8-pin PCIe output from the two existing cables? Will your GTX 3080 start up with only two 8-pin cables connected or do you need all three power inputs?

Are you perhaps considering one of these 1-to-2 adapters?
https://www.amazon.com/Express-Adapter-Graphics-splitter-TeamProfitcom/dp/B0796NVNY7

It's alright, you'll only be pulling up to 300W from an 8-pin CX550 lead rated at 150W. What could possibly go wrong if you "limit" the GPU power? You might only overload the 150W CX550 cable with 200W instead of 300W.

You probably won't notice any melted plastic due to overheating wires and contacts, unless the magic smoke appears.

Just remember what happens to some 600W 12VHPWR connectors when they get too hot. Are you prepared for a fire? Best of luck.

Thank you for the reply.

At first, I thought I could use a 2×Molex to 8-pin or a 2×SATA to 8-pin cable—I know each connector should be connected to separate cables—but I saw that they are kinda risky. So, I am not gonna do that.

I also monitor the PC power draw via a wall outlet power meter—on the FSP. So far, the power draw hasn't exceeded 530 watts. (I know about power spikes and all.)

Molex to 8-pin cable:

https://imgur.com/rdlAmCQ

View: https://imgur.com/rdlAmCQ


SATA to 8-pin cable:

https://imgur.com/X3I2H7Y

View: https://imgur.com/X3I2H7Y

 

[fruko]

Which CX550 do you have? CP-9020121 or CP-9020277? It really does matter because one of the two is a trash group regulated unit.

CP-9020121, the grey-labeled one.

When I was looking for a PSU, I stumbled upon a PSU tier list on Reddit and looked at each PSU's tier letter and notes in the spreadsheet that's in my local market. It was saying the gray-labeled one to be the better one and the black-labeled one to be the crappy one.

 

[Misgar]

I think I'd go with the old fashioned Molex connector option.

The Wiki page shows the Molex pins are rated up to 11A, depending on wire gauge. 12V at 11A = 132W. With two Molex connectors in parallel, that's 264W max. An 8-pin PCIe is rated at 150W. Much lower than 264W, so there's plenty of over-capacity (not that the GPU should draw more than 150W per 8-pin connector if designed properly).
https://en.wikipedia.org/wiki/Molex_connector

The SATA power connectors are rated at much lower level (only 4.5W if this article is to be believed) but I think the author means 4.5A total (3 pins), not 4.5W. Some non-tech people get their Volts, Amps and Watts mixed up. Dunno why.
https://driveshero.com/how-much-power-can-a-sata-cable-support/

This link mentions 1.5A per pin for SATA. With three 12V pins on a SATA power connector that's 3 x 1.5 x 12 = 54W. With two SATA power connectors in parallel it's 108W which is much lower than the 150W rating of 8-pin PCIe. Not safe. Too much risk of overheating.
https://electronics.stackexchange.com/questions/245941/what-is-the-power-specification-for-sata

CAUTION: Do not use that SATA adapter. It's badly under-rated at 108W instead of 150W. Pulling too much current through a SATA connector may cause it to melt and catch fire. Be sensible.

https://forums.redflagdeals.com/wes...burning-hole-my-carpet-pics-included-2338796/

The Molex adapter might be able to supply up to 262W, which is well over the 150W rating of PCIe 8-pin. This should be a slightly "safer" option but it's still not ideal. Cheap adapters have been known to catch fire.

 

[fruko]

I think I'd go with the old fashioned Molex connector option.

The Wiki page shows the Molex pins are rated up to 11A, depending on wire gauge. 12V at 11A = 132W. With two Molex connectors in parallel, that's 264W max. An 8-pin PCIe is rated at 150W. Much lower than 264W, so there's plenty of over-capacity (not that the GPU should draw more than 150W per 8-pin connector if designed properly).
https://en.wikipedia.org/wiki/Molex_connector

The SATA power connectors are rated at much lower level (only 4.5W if this article is to be believed) but I think the author means 4.5A total (3 pins), not 4.5W. Some non-tech people get their Volts, Amps and Watts mixed up. Dunno why.
https://driveshero.com/how-much-power-can-a-sata-cable-support/

This link mentions 1.5A per pin for SATA. With three 12V pins on a SATA power connector that's 3 x 1.5 x 12 = 54W. With two SATA power connectors in parallel it's 108W which is much lower than the 150W rating of 8-pin PCIe. Not safe. Too much risk of overheating.
https://electronics.stackexchange.com/questions/245941/what-is-the-power-specification-for-sata

CAUTION: Do not use that SATA adapter. It's badly under-rated at 108W instead of 150W. Pulling too much current through a SATA connector may cause it to melt and catch fire. Be sensible.

https://forums.redflagdeals.com/wes...burning-hole-my-carpet-pics-included-2338796/

The Molex adapter might be able to supply up to 262W, which is well over the 150W rating of PCIe 8-pin. This should be a slightly "safer" option but it's still not ideal. Cheap adapters have been known to catch fire.

Thanks for the info.

There are practically no good-quality adapters where I live, so I'll stick with FSP.