Hi, I'm setting up a 13 gpu rig, and I'm having an hard time trying to figure out the connection part. Would be really grateful if somebody could help me out!
I got the asrock h110 pro, 13 x asus strix rx570 4gb Gaming OC edition, 3 x EVGA G2 850w PSUs and a bunch of 6pin risers.
All the cables I have at the moment are the ones provided with the 3 PSUs.
 
I was thinking about using 1 PSU to power the mobo and 3 GPUs, and use the other 2 PSUs to power 5 GPUs each.
I have 4 VGA ports on the PSU, so I was thinking about using them to power the 8pin connection on the 4 GPUs, and to power the fifth GPU with a molex to 8pin adapter. Is this safe?

My biggest headache is powering all the risers. Should I order different cables to connect 6pin to 6pin straight from the PSU? Convert from molex to 6pin? Buy different risers and use molex?
 
Thanks a lot

Thanks for the help!
I've bought some extra EVGA cables for my PSUs and I'm leaning towards powering each GPU + riser with a single 6+2/6 Pin PCI-e Cable from a VGA port, so I could power the riser directly with a 6 pin (through a short 6pin extension). Considering I'm using rx 570 4gb, it's a pretty safe choice right?

Still not sure how to power the 13th GPU with a total of 12 VGA ports. If molex to 8pin is not ideal, what other choices do I have? 8 pin splitter, 2 GPUs on a single cable?
 

You're probably going to have to dig up a custom "CPU port to PCI-E power connector" cable from somewhere to make 5 cards + risers work on an EVGA G2 850 - you just don't have enough ports on the PS to handle 5 cards easily, since EVGA uses different pinouts on the PS side for it's VGA and CPU ports - and even THEN you're going to have to use a 6-pin PCI extender to be able to reach one of the risers from one of your "dual VGA" cables.
 
Alternatively, if you can dig up a couple of extra "dual" EVGA PCI-E cables, you can do the following.
 
 Use a dual cable on each VGA port.
 Use a MOLEX string on 3 the Periph/SATA ports - use only ONE Molex connector per string on each port (EVGA has specified these ports/cables ARE interchangeable).
 8-pin connectors on the PCI-E cables power 4 of the GPUs
 2 of the 6-pin connectors get used via a dual-6-pin adapter to power card 5.
 The other 2 6-pin adapters get "extender" cables to be able to reach and power 2 of the risers.
 The other 3 risers are powered from MOLEX.
 
 This leaves ONE Periph/SATA port on the PS to power a couple of fans with, or whatever.
 
 This shortage of ports on the EVGA G2 850 is why all my 5-card rigs are all running Seasonic X-850 or SS-860 power supplies (and when I run out of those I plan to get some Corsair AX-860 as it's basically the SS-860 in a Corsair case) - those have "CPU" ports with the same connection on the PS side as the VGA ports so they end up with *6* ports that can be used interchangeably for CPU or VGA, and they also have 5 SATA/Peripheral ports.