Energy prioritzing & management, and CPU cable splitting for GPU

[Chef-009]

// Thanks in advance for reading. Please don't ask why, just try to answer the questions and don't come up with alternative solutions or rant about the power supply, it's fine.  . It's been a long day... //

 

I've landed in a situation where I'm one 12V PSU cable short for a second 8-pin power connector to power a Quadro RTX 8000. I have multiple questions:

1. Can someone explain to me how a GPU (or maybe even Asus' Hyper M.2 x16 card, or any other PCIe device) pulls power from the motherboard and / or power supply? Does it try to pull 75W from the PCIe socket first? In my case only 20 from the 24-pins are connected to the mobo because of the 8-pin power connectors for the GPU. Would the Asus Hyper PCIe card get in trouble with this? Does the GPU first pull the full 150W from one 8-pin and then the other, or is the load spread over both at the same time? And has the absence of 75W PCIe delivery any effect on this or does it use 3V and / or 5V lines for that?

 

2. I was about to ask if splitting a 12V CPU cable would be possible but then realized the PSU and cable wouldn't know which way to send the current. The wrong way will probably screw with the CPU. But why is it then that I can hook up multiple HDD's to the same cable? (My CPU underclocks heavily when the GPU gets loaded so it potentially opens up the use of a cable that, at that time, theoretically is not needed. Unless the CPU always need two 12V cables to function ofcourse.

 

3. Is splitting one CPU power cable even necessary? Could I just split another 12V cable, already in the 2nd 8-pin connector, just like a 2nd molex connector using the same cable to the PSU as the first one (it splits back out from the first one). What would be the maximum current for one 12V cable?

 

4. Bonus question: If you're working with 4K or 8K video footage on local storage (no nas or server) inside your PC. Is 128GB RAM enough? And would you rather choose a Quadro 8000 in SLI with a standard M.2 PCIe4 SSD -OR- at least 8TB of 15GBytes/s storage with one Quadro 8000?

 

Again, thanks for reading all of that and hopefully answering some of my questions.

[Bombastinator]

I’m reading this as “I bought a gigantor multi thousand dollar Uber GPU that pulls hundreds of watts and my ancient PSU can’t handle it so I want to try some weird tricks to get it to work”

 

This strikes me as several kinds of really bad idea just in general. PSU stuff done wrong can destroy other hardware.  Like that gigantor multi thousand dollar GPU (along with everything else in the box) 

[thrasher_565]

12 minutes ago, Bombastinator said:

I’m reading this as “I bought a gigantor multi thousand dollar Uber GPU that pulls hundreds of watts and my ancient PSU can’t handle it so I want to try some weird tricks to get it to work”

 

This strikes me as several kinds of really bad idea just in general. PSU stuff done wrong can destroy other hardware.  Like that gigantor multi thousand dollar GPU (along with everything else in the box) 

people gotta have budgets you no....

[Chef-009]

8 minutes ago, Bombastinator said:

I’m reading this as “I bought a gigantor multi thousand dollar Uber GPU that pulls hundreds of watts and my ancient PSU can’t handle it so I want to try some weird tricks to get it to work”

 

This strikes me as several kinds of really bad idea just in general. PSU stuff done wrong can destroy other hardware.  Like that gigantor multi thousand dollar GPU (along with everything else in the box) 

It's a brand new PSU actually, but I'm under nda and I can't tell you which one. I tested it and checked everything before so nothing bad happens to the other brand new hardware. But besides that it's new.

[thrasher_565]

1 minute ago, Chef-009 said:

It's a brand new PSU actually, but I'm under nda and I can't tell you which one. I tested it and checked everything before so nothing bad happens to the other brand new hardware. But besides that it's new.

two psu then...

[Chef-009]

1 minute ago, thrasher_565 said:

two psu then...

Sorry, not gonna fit. (Also, this power supply is the only one that will fit xd )

[thrasher_565]

1 minute ago, Chef-009 said:

Sorry, not gonna fit.

its for temp... not long term....

[Chef-009]

1 minute ago, thrasher_565 said:

its for temp... not long term....

What do you mean? The solution I'm working on is supposed to be not just long term, but very long term; and elegant and clean while I'm at it.

[Bombastinator]

4 minutes ago, Chef-009 said:

Sorry, not gonna fit. (Also, this power supply is the only one that will fit xd )

Doubling PSUs never fits.  It would sit next to the machine and there would be wires everywhere.

[thrasher_565]

6 minutes ago, Chef-009 said:

What do you mean? The solution I'm working on is supposed to be not just long term, but very long term; and elegant and clean while I'm at it.

look man you said it was under nda i was thinking that you do what you need to do then spend it off but i guess if you keeping it then ya 2 psu/ buy a better psu are your options. you could splice from another 6 or 8 pin that will work too.

 

i mean if its bran new and under nda no one is going to no how the power delivery works...

 

my pc can take 6 pus.... just saying haha

Edited June 18, 2020 by thrasher_565

[PriitM]

3 hours ago, Bombastinator said:

I’m reading this as “I bought a gigantor multi thousand dollar Uber GPU that pulls hundreds of watts and my ancient PSU can’t handle it so I want to try some weird tricks to get it to work”

 

This strikes me as several kinds of really bad idea just in general. PSU stuff done wrong can destroy other hardware.  Like that gigantor multi thousand dollar GPU (along with everything else in the box) 

buys $5000 GPU...cheaps out on a 1000W PSU worth $300... some people, I tell yah...

[Chef-009]

5 hours ago, PriitM said:

buys $5000 GPU...cheaps out on a 1000W PSU worth $300... some people, I tell 

I did *not* cheap out on the PSU, it's one of the most expensive PSU's I've ever seen. (The wattage is perfectly fine btw.) But I can't change the model. That's why I asked for a direct solution instead of people telling me it's a bad idea and try something else.

[Chef-009]

8 hours ago, thrasher_565 said:

look man you said it was under nda i was thinking that you do what you need to do then spend it off but i guess if you keeping it then ya 2 psu/ buy a better psu are your options. you could splice from another 6 or 8 pin that will work too.

 

i mean if its bran new and under nda no one is going to no how the power delivery works...

 

my pc can take 6 pus.... just saying haha

It's a new one in the sense that I bougt it new (the most recent one made, even). The model itself is several years old. Its i/o is just that of a regular ATX power supply. But that shouldn't have affect my questions much since a PSU is "dumb" hardware.

[Bombastinator]

6 hours ago, PriitM said:

buys $5000 GPU...cheaps out on a 1000W PSU worth $300... some people, I tell yah...

PSU model wasn’t mentioned that I could see.  Just a lack of PSU cables

[Chef-009]

31 minutes ago, Bombastinator said:

PSU model wasn’t mentioned that I could see.  Just a lack of PSU cables

It's usually so that if you lack PSU cables the power supply won't be powerful enough anyway and therefore cheap. But not in this case.

[Bombastinator]

11 minutes ago, Chef-009 said:

It's usually so that if you lack PSU cables the power supply won't be powerful enough anyway and therefore cheap. But not in this case.

The big problem is PSU cables are engineered and tend to be proprietary.  Messing with them is generally a bad idea.  A lot needs to be known about the inner workings of that specific cable on that specific PSU and what it is actually attached to.  To make it more fun opening PSUs is not safe because there are big caps with big joules one there.  Touching the wrong thing can kill you (not kidding. Zap, pow! to quote west side story)

If this NDA is for the PSU (could be, there’s a real lack of info of the specifics of the PSU) you might be able to leverage it to get access to an engineer from the manufacturer that can give you the skinny on what exactly is in the specific box you have.

[kkpatel87]

20 hours ago, Chef-009 said:

It's a brand new PSU actually, but I'm under nda and I can't tell you which one. I tested it and checked everything before so nothing bad happens to the other brand new hardware. But besides that it's new.

You should be able to get a wire diagram and schematic from the manufacturer if you are under NDA. This will tell you what the internals look like and where you can tap off of. I would not recommend any changes to the PSU wiring or internals if you dont have a good grasp of electrical standard concepts and practices.

 

10 hours ago, Bombastinator said:

If this NDA is for the PSU (could be, there’s a real lack of info of the specifics of the PSU) you might be able to leverage it to get access to an engineer from the manufacturer that can give you the skinny on what exactly is in the specific box you have.

Bingo.

 

20 hours ago, Chef-009 said:

3. Is splitting one CPU power cable even necessary? Could I just split another 12V cable, already in the 2nd 8-pin connector, just like a 2nd molex connector using the same cable to the PSU as the first one (it splits back out from the first one). What would be the maximum current for one 12V cable?

I dont think you quite understand. Ampacity, or maximum current carrying capability of a wire, is calculated with the insulation rating, wire gauge, ambient temperature, harness bundling, load profile, etc. If you can get all that information, you can use the Neher-Mcgrath method to solve for the ampacity for your particular wiring. There are some rules of thumb but those can vary wildly. PSU cabling is pretty cheap and do not have much margin to carry extra amperage. Plus the terminals on the mini-fit jr connectors have a max rating of about 13A depending on the wire and terminal itself.

[thrasher_565]

 the way i understand it is there is a wad of 12v wires (aka yellow) and a wad of black wires (aka ground) and the all get solderd to the pcb in one big wad. the fatter the cable the more amps it can handle. but is most cases i doute the each cable  is being used at its max ratting. people a few uses a go were using gpu spliters to 1 cable to the gpu instead of 2 to make it "cleaner" and there were no side affects as far as im aware.... i mean you can add up what each computen is using in power and get a good idea of were you at for amps. a wat meeter will tell you the total wats pulled from the wall. and there are psu that can do 1800 wats at w/e the cable rating for amps. if you really need Moore then what 1 cable is using then just use 2 cable to make it fatter. but i think that will increas that amps but drecres the wats i think....

 

if the wire is to small it gets hot and can burnout.

 

i have been zapped by a psu in electronics class were i used a  psu to power a 80mm fan instead of the amp transformer because it was free and i had space. (also put a cd drive in there also...

 

i do agree that oping and messing with it is a bad idea but you do you....

[thrasher_565]

13 hours ago, Chef-009 said:

It's a new one in the sense that I bougt it new (the most recent one made, even). The model itself is several years old. Its i/o is just that of a regular ATX power supply. But that shouldn't have affect my questions much since a PSU is "dumb" hardware.

i stll don't get why its under nda if its old then it cant be under nda.... i don't no man im at a loss i don't no about server hardware only pc hardware so im out for now...

 

what im thinking is that is say an voodoo 6000 seal in a box.... that would make it old but new as its still in the box but voodo is gone so no nda unless you singed some papers the no reveal it...

 

 

[Chef-009]

@thrasher_565 @kkpatel87 @Bombastinator @PriitM Thanks guys, it's solved now. I've learned quite a lot the past few days. I asked the manufacturer for the datasheet and pieced everything together, and it actually works. Thanks again!