Risers

[Nix94]

Hi i have 4x MSI Armor RX 580 8GB and i have this risers

 https://www.amazon.com/Lesofod-Extender-Graphics-Extension-Powered/dp/B076MP4M8W/ref=sr_1_1_sspa?ie=UTF8&qid=1521081066&sr=8-1-spons&keywords=risers&psc=1

 my PSU is

 https://www.evga.com/products/product.aspx?pn=220-P2-0850-X1


So iam looking for the best way to power that risers

[gsanjin]

You can power two risers using 4-pin molex cable (it can handle 2x75W), then two other risers with SATA but with separate SATA cables, just for case. Power VGA's using four available VGA power cables.

[QuintLeo]

You can power two risers using 4-pin molex cable (it can handle 2x75W), then two other risers with SATA but with separate SATA cables, just for case. Power VGA's using four available VGA power cables.

2 risers on a molex string is NOT a  good idea on an EVGA B2/G2/P2/T2 series power supply - even if the wiring is sized for it (it's NOT) the power supply ITSELF is only rated for 75 watts per Peripheral/SATA port according to a post in the EVGA forums BY AN EVGA EMPLOYEE.
The "SATA" and "Periph" ports ARE interchangeable - same pinout on the PS side - and worst case EVGA will sell you spare cables, usually fairly inexpensively.

Could also use one of the "dual" PCI-E cables to power 2 risers, but you'll need a total of 3 "dual" cables so you can use a 2 x 6 pin PCI-E to 8-pin PCI-E adapter to power one of the cards with.
It would also be practical to use a 6-pin PCI-E "extender" on each of 2 dual cables, powering one GPU and one riser from the same cable - which might be the best option.

Powering risers with SATA is risky - the connector ITSELF is only rated for 54 watts, the riser ITSELF soaks a few watts in the "voltage conversion" circuitry, and the PCI-E bus is RATED to provide up to 75 watts of power.
It might work OK if your GPU pulls 50 watts or less out of the PCI-E bus - but there is no way to CONTROL that and some cards (particularly some AMD Polaris models) were notorious for EXCEEDING the 75 watt rating on peaks.

[jillscarbrough]

That PSU has 4 Molex 4 Pin's but on one rail. You can only power two risers using that 4 Pin's Molex for safety.

For SATA connector, risers powering terms for safety.
Use only one SATA connectors per rail for powering risers. Yes, SATA would produce max 54W, but GPUs would draw power as much as needed only. And they have powered by PCIe cable.

EVGA SuperNOVA 850 P2 has ten SATA connector from four different rails. So, you can use two SATA rail to powering two risers, and the other use for HDD/SSD or maybe another part.

For your reference:
SATA

MOLEX


Source: http://www.gpuminingresources.com/p/psu-cables.html

[QuintLeo]

That PSU has 4 Molex 4 Pin's but on one rail. You can only power two risers using that 4 Pin's Molex for safety.

For SATA connector, risers powering terms for safety.
Use only one SATA connectors per rail for powering risers. Yes, SATA would produce max 54W, but GPUs would draw power as much as needed only. And they have powered by PCIe cable.

EVGA SuperNOVA 850 P2 has ten SATA connector from four different rails. So, you can use two SATA rail to powering two risers, and the other use for HDD/SSD or maybe another part.

Source: http://www.gpuminingresources.com/p/psu-cables.html

Per EVGA THEMSELVES, the PORT that the Molex string is connected to on the PS is only rated 75 watts.
DO NOT look at that 300 watt rating on the connector (which would be 288 watts ONLY if it had 3 pins each on +12VDC and ground) and think it applies to the PSU PORT itself.

Additionally, with only ONE PIN on 12VDC on the connector (the others are used for SATA-related voltages) you have a max of 96 watts for the CONNECTOR ITSELF on the PSU end.

2 risers on one molex string on an EVGA B2/G2/P2/T2 series power supply = ASKING FOR MELTDOWN and is actually WORSE than powering one riser from a SATA connector.


As already stated, you have ZERO CONTROL over how much power a GPU pulls out of the PCI-E bus vs the PCI-E power connector (they DO NOT always, IF EVER, prioritise the power connector) so there is no way to be sure that a SATA power connection to a riser is going to be safe unless you actually MEASURE the draw, or the card pulls less than about 50 watts TOTAL for the entire card (GTX 750 ti or HD 7750 - the GTX 1050/1050ti CAN'T be turned down that far, though at minimum 52.5 watts they're at least close).

The draw is not always "proportional" to the TDP setting as well - some cards appear to draw power for their memory and/or video output circuitry from the PCI-E bus while powering the GPU itself from the 6/8/multiple power connector(s) so turning the TDP down will have almost ZERO effect on the draw from the PCI-E bus.


That "gpuminingresources" site has obviously never owned and looked at the cabling on a EVGA B2/G2/P2/T2 series power supply, or bother reading the EVGA forums - their so-called ratings are JUNK and not to be trusted, if they thing you can pull 300 watts from the SATA/PERIPERAL ports on that PS series.


 

[jillscarbrough]

That PSU has 4 Molex 4 Pin's but on one rail. You can only power two risers using that 4 Pin's Molex for safety.
-Snip-

Per EVGA THEMSELVES, the PORT that the Molex string is connected to on the PS is only rated 75 watts.
DO NOT look at that 300 watt rating on the connector (which would be 288 watts ONLY if it had 3 pins each on +12VDC and ground) and think it applies to the PSU PORT itself.

Just ignore about power rating, I posted that pic just for show how many connectors would have full power for each rail.
Total power draw by GPUs is combining between PCIe Cable and PCIe bus.  GPUs can draw up to 75 watts through the PCIe bus, but not always. In facts, I use SATA (one rail one Riser) to powering Risers for my R9 390/390x, 290/290x, almost two years with no issue. It is isn't technical, this is the real experience.
 

As already stated, you have ZERO CONTROL over how much power a GPU pulls out of the PCI-E bus vs the PCI-E power connector (they DO NOT always, IF EVER, prioritise the power connector) so there is no way to be sure that a SATA power connection to a riser is going to be safe unless you actually MEASURE the draw, or the card pulls less than about 50 watts TOTAL for the entire card (GTX 750 ti or HD 7750 - the GTX 1050/1050ti CAN'T be turned down that far, though at minimum 52.5 watts they're at least close).

The draw is not always "proportional" to the TDP setting as well - some cards appear to draw power for their memory and/or video output circuitry from the PCI-E bus while powering the GPU itself from the 6/8/multiple power connector(s) so turning the TDP down will have almost ZERO effect on the draw from the PCI-E bus.

May it depends on a company that designed the card. Some cards draw from the PCIe slot to the fullest, and some other use it only to power fans and LEDs. It explains why some people haven't an issue using "one SATA for one Riser." for a long time running. And the other people get in trouble with it, And also depends on which PSUs they are using. (again, based on experience)

[Nix94]

Couple of people recommended me that i should use the VGA cable i have 4 VGA cables with 6+2 and 6+2 on one string so with the first 6+2 i powered the GPU and then with the second one i powered the riser of course i bought extenders 6pin to 6pin what do you think about that ?

[leonix007]

Couple of people recommended me that i should use the VGA cable i have 4 VGA cables with 6+2 and 6+2 on one string so with the first 6+2 i powered the GPU and then with the second one i powered the riser of course i bought extenders 6pin to 6pin what do you think about that ?

that is fine, with this setup it could actually look much neater in terms of wire managements. in terms of power handling the wire could possibly handle both GPU and riser

[jillscarbrough]

Someone has been done PCI Riser power test and give us the results and recommendations. But still, it would depend on a few factors, as we discussed above.

Here is the link to the post: PCI Riser Power Test, Results, and Recommendations

[QuintLeo]

Couple of people recommended me that i should use the VGA cable i have 4 VGA cables with 6+2 and 6+2 on one string so with the first 6+2 i powered the GPU and then with the second one i powered the riser of course i bought extenders 6pin to 6pin what do you think about that ?

Perfectly viable and safe for any RX 470/480/570/580 model.