Question DOA. Can I use PCIe power connector to power the CPU?

[Ancipital]

So, my new MSI power supply came DOA. I have all parts for my new computer except the PSU and I want to build it NOW.

I have an old power supply that only has one connector for CPU. My motherboard requires two connectors.
Can I use one on the PCIe rails to power the CPU?
They have the same connector and the same voltage (I measured 12V on both of them). The PCIe rail is rated for higher amperage.
It should work. Right?

-----------------

New PSU (DOA) is: MSI MPG A750 GF
Old PSU: Antec HCG 750 (worked for 12 years, still works today).
MOBO: Gigabyte X670 Gaming X AX V2

 

[Lutfij]

I have an old power supply that only has one connector for CPU. My motherboard requires two connectors.
Can I use one on the PCIe rails to power the CPU?
When posting a thread of troubleshooting nature, it's customary to include your full system's specs. Please list the specs to your build like so:
CPU:
CPU cooler:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
OS:
Monitor:
include the age of the PSU apart from it's make and model.

I made a shortcut between the 4th pin and the ground (green and black).
Even if the paperclip test got the PSU to work, it doesn't indicate how much power the PSU can effectively deliver to your components.

Moved thread to Systems section from Motherboards section. Please stick to one thread, unless you want spaghetti brains

 

[CountMike]

So, my new MSI A750GH power supply came DOA.
I made a shortcut between the 4th pin and the ground (green and black). You can hear something (like a relay) inside the PSU trying to start. The cooler does not spin. Seems kaput.
Ideas before I send it back?

I will like to use my old power supply but it only has one CPU connector: https://forums.tomshardware.com/threads/doa-can-i-use-pcie-power-connector-to-power-the-cpu.3863808/

That test proves nothing except that PSU has some power so it's useless.
To answer firs question, NO. you can't use PCIe connectors or cables for CPU aux power.
If both PSUs are (semi)modular you MUST use cables that came with it, don't even bother trying any others or you could burn everything.

 

[Ancipital]

That test proves nothing except that PSU has some power so it's useless.
To answer firs question, NO. you can't use PCIe connectors or cables for CPU aux power.
If both PSUs are (semi)modular you MUST use cables that came with it, don't even bother trying any others or you could burn everything.

Thanks

New PSU (DOA) is: MSI MPG A750 GF
Old PSU: Antec HCG 750 (worked for 12 years, still works today).
MOBO: Gigabyte X670 Gaming X AX V2

 

[CountMike]

Thanks

New PSU (DOA) is: MSI MPG A750 GF
Old PSU: Antec HCG 750 (worked for 12 years, still works today).
MOBO: Gigabyte X670 Gaming X AX V2

This one ?
https://antec.com/product/power/hcg-gold750
If it is, you must have lost or didn't get one of two 8(4+4) Pin EPS 12V cables it came with. Maybe you can find to buy buy some for it but I wouldn't bother about 12 year old PSU.
MB ?
https://www.gigabyte.com/Motherboard/X670-GAMING-X-AX-V2-rev-10/sp#sp
you should be ale to get away with only one of those EPS cables unless you are overclocking and /or have many devices using a lot of power. Have you tried at all ?

 

[Misgar]

My motherboard requires two connectors.

When you say "two connectors" are the ATX12V headers on your motherboard both 4-pin, or one 8-pin and one 4-pin, or two 8-pin?

The image below shows one 4-pin and one 8-pin.

I've been running an old motherboard with an 8-pin ATX12V header using a PSU with just a 4-pin cable for several years. It's not the "best" engineering solution, because halving the number of +12V wires will halve the maximum available current and double the ripple voltage on the CPU VRMs, but I'm using a low power CPU and as an electronics design engineer, I'm happy with the solution. I have performed numerous electrical safety design analyses on MIL SPEC systems at work, and it's a "risk" I'm prepared to take.

If your PSU provides an 8-pin ATV12V cable and your motherboard needs another 4-pin ATX12V cable (like the photo above), you can usually get away with just one 8-pin cable, unless the BIOS checks for the prescence of both the 8-pin and the 4-pin cables. Provided you don't overclock your CPU, a single 8-way cable should be sufficient, until your new PSU arrives.

The more +12V wires you connect in parallel to the CPU VRMs, the more current they can supply. If the PSU is constructed using 18 AWG wires and if we assume each wire is rated at 7A (in free air, not bunched), an 8-pin ATX12V cable shoukl be able to provide 4 x 7A = 28A at 12V = 336W - more than enough for most CPUs, apart from heavily overclocked processors like the i9-14900K. That's when you need another 4-pin or 8-pin cable.

If you only have one 4-pin ATX12V cable, that's 2 x 7A at 12V = 168W - enough for a low power CPU without overloading the 18 AWG wires.

 

[CountMike]

When you say "two connectors" are the ATX12V headers on your motherboard both 4-pin, or one 8-pin and one 4-pin, or two 8-pin?

The image below shows one 4-pin and one 8-pin.

I've been running an old motherboard with an 8-pin ATX12V header using a PSU with just a 4-pin cable for several years. It's not the "best" engineering solution, because halving the number of +12V wires will halve the maximum available current and double the ripple voltage on the CPU VRMs, but I'm using a low power CPU and as an electronics design engineer, I'm happy with the solution. I have performed numerous electrical safety design analyses on MIL SPEC systems at work, and it's a "risk" I'm prepared to take.

If your PSU provides an 8-pin ATV12V cable and your motherboard needs another 4-pin ATX12V cable (like the photo above), you can usually get away with just one 8-pin cable, unless the BIOS checks for the prescence of both the 8-pin and the 4-pin cables. Provided you don't overclock your CPU, a single 8-way cable should be sufficient, until your new PSU arrives.

The more +12V wires you connect in parallel to the CPU VRMs, the more current they can supply. If the PSU is constructed using 18 AWG wires and if we assume each wire is rated at 7A (in free air, not bunched), an 8-pin ATX12V cable shoukl be able to provide 4 x 7A = 28A at 12V = 336W - more than enough for most CPUs, apart from heavily overclocked processors like the i9-14900K. That's when you need another 4-pin or 8-pin cable.

If you only have one 4-pin ATX12V cable, that's 2 x 7A at 12V = 168W - enough for a low power CPU without overloading the 18 AWG wires.

There are 2x8pin.

 

[Ancipital]

there are 2 connectors 8 pins each as shown here (top left corner):

 

[Ancipital]

This one ?
https://antec.com/product/power/hcg-gold750

no
My power supply (the old one with a single CPU cable) is this one:
https://www.anandtech.com/show/4258/antec-hcg-750-gaming-psu

Have you tried at all ?

Nope. I was afraid that it will draw too much power.

 

[Ancipital]

I've been running an old motherboard with an 8-pin ATX12V header using a PSU with just a 4-pin cable for several years. It's not the "best" engineering solution, because halving the number of +12V wires will halve the maximum available current and double the ripple voltage on the CPU VRMs, but I'm using a low power CPU and as an electronics design engineer, I'm happy with the solution. I have performed numerous electrical safety design analyses on MIL SPEC systems at work, and it's a "risk" I'm prepared to take.

I will try that until my new PSU comes.
I will lower the cpu frequency from BIOS so the CPU will never use full power.

__________


I figured out what happened with the PSU I got. I got it from Amazon and the box seemed a bit "used". Inside the box, at the very bottom, I have found two metal tabs. Not in a bag - usually everything comes in a plastic bag today. I though they are some kind of accessories for the PSU. Now I realized, there are those metal tabs in the back of the PC chassis/box, that you need to break when you install a new card (like video card).

So, the PSU came used / broken from Amazon!
The seller is Amazon itself.
I guess they received a return that seemed unopened OR one of their employees replaced a new one with his own (broken).

 

[CountMike]

I will try that until my new PSU comes.
I will lower the cpu frequency from BIOS so the CPU will never use full power.

__________


I figured out what happened with the PSU I got. I got it from Amazon and the box seemed a bit "used". Inside the box, at the very bottom, I have found two metal tabs. Not in a bag - usually everything comes in a plastic bag today. I though they are some kind of accessories for the PSU. Now I realized, there are those metal tabs in the back of the PC chassis/box, that you need to break when you install a new card (like video card).

So, the PSU came used / broken from Amazon!
The seller is Amazon itself.
I guess they received a return that seemed unopened OR one of their employees replaced a new one with his own (broken).

I don't remember exactly if it was that model but dew month back there was a series of bad MSI CPUs sold.

 

[Ancipital]

It works with a single CPU cable!