Testing ATX PSUs under load - Does loading the ATX 24 pin also load EPS & PCIE?

[AJ847.63e]

Hi Folks,

Just wanted to clear up a misunderstanding of mine (or what I expect is one). Isn't the 12V rail from the 24 pin, EPS and PCIE separated? IE if I put a power resistor on the ATX 12V pin that is not going to load, thus tell me if the EPS or PCIE rails are fine?

I was recently watching ArIs from Hardware Busters video on how to properly test ATX PSUs without using 5 figure Croma substations.

The PCB adapter he used breaks out the 12, 5 and 3.3V pins from the 24 pin and gives you banana plugs to connect to. That is a bit useless is it not? Aren't the 12V rails from the 24 pin connector, EPS connector and PCIE connector isolated? So loading the 24 pin is only loading the 12V rail from the 24 pin, not the other rails?
The rails where 90% of your load is and thus most likely to fall over?

I'm researching into ideally buying, but if I have to building, a ATX proper load tester and found that mentioned video. We've had so many power supplies in which test fine on a useless PSU tester but falls over under load.

Yes people are going to scream just swap the PSU, this is why you keep known goods. But that is not always practical, especially when you have proprietary PSUs (thank you Dell!). It would be nice to be able to test your patient and put a load on it so you have reasonable information before going and spending 130+ bucks on a replacement PSU to then find out congrats you just wasted 120 bucks the PSU is fine. Or it was the fault and took out the board as well.

Closest think I've found is the PSU Tester V2 from CHWTT. https://www.instructables.com/DIY-AT...Supply-Tester/
Has anyone built this?

Thanks for the info.

[dmill89]

Yeah, it all depends on the PSU...

^This.

though most nowadays are a single rail design. That said, even PSUs with more than one 12V rail still usually have a large main 12V rail internally that is then split-off into "separate" 12V rails via current shunts. The idea behind this concept is so that none of the wires can get over-loaded and burn out... and one reason I'm not really a fan of the modern single-rail "welder" designs. All those are good for is burning holes on GPUs if a MOSFET shorts, particularly on GPUs with VRMs that aren't very quick to react to the short-circuit (or at all.)
.

I tend to agree, though with higher wattage units even with split rails there is often enough amperage on each rail to do some damage if something goes wrong. Examples below the Antec High Current Pro (made by Delta) units where the 1000W unit has 4 40A rails and the 1200W unit has 8 30A rails

But I agree with stj, you have to open the PSU and see.
In the case of single rail split into different ones via current shunts, you should also plug in the EPS 12V and PCI-E power connectors, just to make sure that you don't trip the current limit on each one separately. On PSUs with a single 12V rail, though, this you won't have to worry about.

^ Agree for any PSU that claims to be multi-rail the only way to be sure is to open it up.


To determine if a PSU is single rail or multi-rail (at least by manufacture claims) you can check the label. If it is multi-rail there will be 12V1-12Vx listed on the label like with the aforementioned Antec High Current Pro units:








If it is single rail there will be one entry on the label for 12V like this Seasonic Focus+ 850FX:

[stj]

some psu's are split-rail, some are single.
only way to know is to check continuity or open it and look at the tracks.

[AJ847.63e]

Ok thanks for the confirmation.

[momaka]

Yeah, it all depends on the PSU... though most nowadays are a single rail design. That said, even PSUs with more than one 12V rail still usually have a large main 12V rail internally that is then split-off into "separate" 12V rails via current shunts. The idea behind this concept is so that none of the wires can get over-loaded and burn out... and one reason I'm not really a fan of the modern single-rail "welder" designs. All those are good for is burning holes on GPUs if a MOSFET shorts, particularly on GPUs with VRMs that aren't very quick to react to the short-circuit (or at all.)

But I agree with stj, you have to open the PSU and see.
In the case of single rail split into different ones via current shunts, you should also plug in the EPS 12V and PCI-E power connectors, just to make sure that you don't trip the current limit on each one separately. On PSUs with a single 12V rail, though, this you won't have to worry about.

[dmill89]

Yeah, it all depends on the PSU...

^This.

though most nowadays are a single rail design. That said, even PSUs with more than one 12V rail still usually have a large main 12V rail internally that is then split-off into "separate" 12V rails via current shunts. The idea behind this concept is so that none of the wires can get over-loaded and burn out... and one reason I'm not really a fan of the modern single-rail "welder" designs. All those are good for is burning holes on GPUs if a MOSFET shorts, particularly on GPUs with VRMs that aren't very quick to react to the short-circuit (or at all.)
.

I tend to agree, though with higher wattage units even with split rails there is often enough amperage on each rail to do some damage if something goes wrong. Examples below the Antec High Current Pro (made by Delta) units where the 1000W unit has 4 40A rails and the 1200W unit has 8 30A rails

But I agree with stj, you have to open the PSU and see.
In the case of single rail split into different ones via current shunts, you should also plug in the EPS 12V and PCI-E power connectors, just to make sure that you don't trip the current limit on each one separately. On PSUs with a single 12V rail, though, this you won't have to worry about.

^ Agree for any PSU that claims to be multi-rail the only way to be sure is to open it up.


To determine if a PSU is single rail or multi-rail (at least by manufacture claims) you can check the label. If it is multi-rail there will be 12V1-12Vx listed on the label like with the aforementioned Antec High Current Pro units:








If it is single rail there will be one entry on the label for 12V like this Seasonic Focus+ 850FX:

[AJ847.63e]

Understood, thank you everyone for the info. Still waiting on PCB Way to approve my order so I can order that PSU tester I linked to. Is it normal for a order to be "in review" for almost 2 weeks now?