Question about rails

[IAmAndre]

Hi,

 

I have a Be quiet! Pure Power 11 400W and it struggles to power my system properly although it shouldn't. I have a Ryzen 5 2600X and a Vega 56, which I undervolted/overclocked and currently peaks at 175W in benchmarks. I've seen on YouTube/Google people having this issue and it seems to be fixed by using a second power cable, the problem being that the rail is saturated. However I don't understand how this works.

 

These are the specs of the PSU: +3.3V@24A, +5V@15A, +12V1@24A, +12V2@20A, -12V@0.3A, +5VSB@3A.

 

From what I understand, the CPU and GPU all use the 12V rail, which would mean that their total consumption shouldn't exceed 288W. However, since there are two 12V rails, why can't I just have the PSU use a different rail without having to buy a second PCI cable?

 

Thanks,

[Matty2048]

use hwinfo to see whats happening to your rails e.g. are they being pulled down too much 

 

[OrionFOTL]

You forgot to describe in what way does it struggle to power your system properly.

 

The CPU 4+4pin cable uses the 12V2 rail, while the 24pin cable, PCIe cables and peripheral cables all use the 12V1 rail.

 

3 minutes ago, Matty2048 said:

use hwinfo to see whats happening to your rails e.g. are they being pulled down too much 

 

Software voltage readings are useless because they're never accurate.

[Juular]

According to manual, on 400W version PCIe cables are powered only by 12V rail #1, rail #2 is only powering CPU 4+4 pin cable. And even though 288W (minus some 30-50W for CPU and drives and plus some headroom due to OCP usually being higher than claimed) on 12V rail #1 is technically enough for any GPU out there, AMD Vega has very high transient load spikes which triggers OCP on rail #1. You need to change the PSU or GPU.

[IAmAndre]

5 minutes ago, OrionFOTL said:

You forgot to describe in what way does it struggle to power your system properly.

 

It basically restarts when I run pretty much any game at a resolution higher than 1080p. Well I've only tried demanding games so far such as Rise of the Tomb Raider, Jedi Fallen Order etc. GTA V worked fine though. I even got a restart after I switch from 4k to 1440p on Tomb Raider.

[IAmAndre]

18 minutes ago, Matty2048 said:

use hwinfo to see whats happening to your rails e.g. are they being pulled down too much 

 

Just installed it but how do I check the values?

[IAmAndre]

9 minutes ago, Juular said:

According to manual, on 400W version PCIe cables are powered only by 12V rail #1, rail #2 is only powering CPU 4+4 pin cable. And even though 288W on 12V rail #1 is technically enough for any GPU out there, AMD Vega has very high transient load spikes which triggers OCP on rail #1 (probably around 30A). You need to change the PSU or GPU.

Any idea why using two separate PCIe cables helped some?

[Juular]

3 minutes ago, IAmAndre said:

Any idea why using two separate PCIe cables helped some?

Hmm, the only thing that comes to mind is voltage drop but that shouldn't be an issue here. Regardless, powering AMD Vega with this PSU were a bad idea to start with, AMD Vega is a very tricky GPU.

[IAmAndre]

34 minutes ago, Juular said:

According to manual, on 400W version PCIe cables are powered only by 12V rail #1, rail #2 is only powering CPU 4+4 pin cable. And even though 288W (minus some 30-50W for CPU and drives and plus some headroom due to OCP usually being higher than claimed) on 12V rail #1 is technically enough for any GPU out there, AMD Vega has very high transient load spikes which triggers OCP on rail #1. You need to change the PSU or GPU.

If the CPU is powered by the rail one, wouldn't that mean that rail 2 is dedicated to the PCIe parts, which would mean 288W for the GPU and the drives?

[Juular]

1 minute ago, IAmAndre said:

If the CPU is powered by the rail one, wouldn't that mean that rail 2 is dedicated to the PCIe parts, which would mean 288W for the GPU and the drives?

Read again, or refer to actual manual. On 400W version of Pure Power 10/11, 12V rail #1 powers motherboard 24-pin, SATA and PCI-e cables, rail #2 powers only CPU 4+4 EPS connector.

[IAmAndre]

 

1 hour ago, Juular said:

Read again, or refer to actual manual. On 400W version of Pure Power 10/11, 12V rail #1 powers motherboard 24-pin, SATA and PCI-e cables, rail #2 powers only CPU 4+4 EPS connector.

Well I'll see what happens with a new cable.

[IAmAndre]

3 hours ago, Juular said:

Hmm, the only thing that comes to mind is voltage drop but that shouldn't be an issue here. Regardless, powering AMD Vega with this PSU were a bad idea to start with, AMD Vega is a very tricky GPU.

Does this confirm my theory? 

Here are the specs of the HX1000i according to Newegg:

 

 Single +12V Rail Mode: +3.3V@25A, +5V@25A, +12V@83.3A, -12V@0.8A, +5VSB@3A Multiple +12V Rail Mode: +3.3V@25A, +5V@25A, +12V1@40A, +12V2@40A, +12V3@40A, +12V4@40A, +12V5@40A, +12V6@40A, +12V7@40A, +12V8@40A, -12V0.8A, +5VSB@3A

 

[Juular]

@IAmAndre As you can see, Corsair HX1000i has 8 12V rails, don't remember exactly but out of those, 6-7 are used by GPU connectors probably, whereas your PSU only has one rail for GPU connectors.