Bitcoin Forum

Hi there.
So, I bought 2 of those https://www.amazon.com/KKmoon-Switching-Efficiency-Ethereum-180-260V/dp/B077JD399B/ref=sr_1_6?ie=UTF8&qid=1529180530&sr=8-6&keywords=kkmoon+switching for my 2 vega rigs of 6 cards each, and it works fine.
Now, since it has 12x 6+2 pin, I was going to try it also for a 12x 570 rig.
The problem is that it comes with 4 cables, each with 2x sata and 2x moles, and if I had to follow the "rule", I could only power 2 risers with each cable (got the 6pin to sata risers), so 4 risers left.
Also, I need 2x sata connectors for the mobo (those for multiple gpus)..
Would it be risky to run 3 risers on each cable, with mixes sata and molex connectors? Also considering that 2 of those cables would have the 4th connector on the mobo.
Thanks!

I think 3 PCI-e risers on one cable is ok. As you said, the rule is 2 connections per riser. I have a bunch of rigs that use 3 risers for a single cable. Although the 4th connection to the motherboard is a little worry-some to me. I think you will be able to do it. Just keep an eye on cable temps. If you touch it and it is warm, you might want to reconsider your riser setup. You can also buy a $30 laser temperature gun from Home Depot to tell you the temps accurate within 5 degrees Fahrenheit. Better to use an infrared camera, although pretty expensive.

When doing the 3 connections per riser make sure your hashrate matches others hashrates. If they are the same and the setup is stable you should be all good. Don't 100% take my word for it though, I'm not an extreme mining expert, just talking from my own experiences.

All depends on the thickness and quality of the cable. If its less than 18awg then i wouldnt do more than two risers per cable. 18-16awg no problem with three really. Be careful with cheaper electronics gear as sometimes they mark the cable one gauge but the actual copper strands are alot thinner inside.

I would recommend against powering more than two risers with SATA connectors on 18 AWG cable. The problem with powering more than two risers per SATA strand is 18 AWG wire is only rated for 10 A max for single core wire, which is 120 W at 12 V and much less for multi-stand wire. SATA connectors also have a single 12V wire, which means the entire load is on a single cable, instead of spread out over 2 or 3 cables as is the case with 6 or 8 pin PCI-E cables. Using more than two risers per SATA cable strand WILL exceed the rating of 18 AWG multi-stand wire, causing the wire to heat up and is dangerous.

https://www.engineeringtoolbox.com/wire-gauges-d_419.html

In the case of 6-pin powered PCI-e risers, do you think powering more than 2 risers will be an issue?

In most cases I would keep it to two risers per cable max. Each riser can pull over 50W depending on the card and algorithm, such as with dual mining. A 6-pin PCI-E connector is only rated to deliver 75W max and a RX 580 dual mining can easily pull over 50 W from the riser. Some PSU's like EVGA, have cables with a 8-pin and a 6-pin pigtail, or with dual 8-pin's. In that case it should be OK to use a 8-pin to dual 6+2 splitter on the 8-pin connector which is rated to deliver 150 W and then the 6-pin to power 3 risers off one PSU cable.

Some server type PSU's that come only with 6-pin connectors have thicker gauge cable coming from the PSU that then braches off in to 18 gauge to each individial 6-pin connector. In that case you might be able to use a splitter on the 6-pin to power two risers from each 6-pin on the PSU if needed.

Super agree with Vann
Most of the consumer PSUs only have max 2 x 6pins connectors each rail (6pins - 6+2pins PCIe), except you are using a Y splitter. And the other things related to max power rated has posted above.

Powering a riser also will depend on the graphics card you are using, each brand, each series has different power management related to the power used priority (PCIe bus or direct PCIe socket that will load at first)

 

These chinese PSU are built for 6 GPUs, and not 12.
It mentions having 12 PCIE cables for GPUs with 8+6 power connectors. But in reality, they are meant for 6 GPUs usage.

Do not connect the motherboard's SATA/Molex sockets that are near the PCIE slots if you are going to power the risers directly, and I do not recommend using powering the risers from the motherboard at all; with 12 PCIE slots, that means you can have upto 900W going through the motherboard, which is alot.
Always power the risers directly from the PSU using SATA or 6pin PCIE.

The risers can consume upto 75W of Power (though its rare you will reach that point), but powering 3 risers using 1 PCIE/SATA/Molex rail can melt your cables or blow the fuse or in the case of chinese PSUs, the whole PSU will not work (I use these chinese ones as well.. very cheap).
It happened several times with me; I had EVGA modular PSUs, 3 risers on one rail; some of the cables melted and I had to replace them, but that was during the dual mining era.. doubt it will ever happen if you are single mining, the whole GPU barely consumes 110W.