Powered Risers with 2 PSU's?

[fatrobotsneedlove]

So there seems to be concern on mining forums that using 2 PSU's with powered risers can fry everything if not connected in a specific way (something about a 12V+ feedback loop).

https://litecointalk.org/index.php?topic=6171.0

Some seem to think the molex pins for the risers just need to be connected to the same PSU as their respective GPUs. Other people say the risers and the GPUs both need to be connected to the same PSU as the motherboard. Other people say Add2PSU solves this problem somehow. Even different people say that the 12V+ wire from the riser to the mobo should be CUT, like, with scissors, so only the molex pin is sending power into the riser.

Anyone know? I have everything but don't want to accidentally fry my titans experimenting.

[glimpse]

hi, man.

You'll not fry Your Titans but motherboard can be cooked with more than 4cards..back to x58 days we've seen some 4cards rig got bad..

now I've read 'bout this issue earlier, but it seems noOne has concrete standing answer. The best practice (especially when building rigs for such applictions like OctaneRender) is seating 4cards cards directly into motherboard (for stability issues)

If You are messing with multiple GPUs hook molex on Your main PSU - the reason doing so is to have power as early as possible once Your rig boots, so cards would not start drawing too much energy from motherboard.

However in these days higher-end mother boards have at least extra 6pin & if You step crazy using more than 4cards..with powered raisers & I'd advice to use single & GOOD power supply..

buying high-end GPUs for thousands but try to save 100$ for PSU is just not good idea at all =) as You save too little & put stability of entire system at risk..cutting corners (because of added complexity) will always add another point of failure - keep things simple!

[fatrobotsneedlove]

Thanks for the reply glimpse!

I have two evga 1300G2's, which are pretty good. I didn't get something like a 1600W platinum because I figured no one PSU could ever power six gpus. Just recently came across the riser/2 psu issue.

So, I guess maybe the best idea would be to seat 3 of the gpus directly on the mobo (powered from the second PSU), then use risers for the other three (powered from the first PSU that is also powering the mobo)? That would restrict the airflow more than a big mining style open case with six risers, but obviously beats a fried motherboard.

[glimpse]

what is Your exact hardware? what motherboard You're using?

[fatrobotsneedlove]

what is Your exact hardware? what motherboard You're using?

Asus X99 E-WS mobo, 2 EVGA 1300G2 PSU's with an Add2PSU to connect them, i7-5820K, 2 Titan Blacks and 4 gtx 780 with 6gigs vram.

Also these risers...
http://www.moddiy.com/products/PCI%252d ... cm%29.html

[fatrobotsneedlove]

If it really is this much of a concern though, as a lot of stuff seems to suggest, I might just get another mobo and throw the extra two cards on that (and maybe add one or two extra cards ) Definitely don't want to F everything up trying to squeeze everything together.

[glimpse]

Well, there are 2kW PSU - enough to keep Your rig happy, as You'll top out around 1600W with that setup on full load while rendering in Octane =)

As for mobo & handling 6GPUs, honestly, I'd go straight to ASUS & talk to someOne like JJ (working' with ASUS) to give his recommendations, but I have a feeling this workstation motherboard should be able to lift of with those GPUs =)

even if You free something out You should be able to get motherboard changed & investing that much into hardware to build separate system, buy one more set of licence..I don't know..seems a bit like a stem backwards =) but hey..don't take my word, do research..talk with proper companies representatives & pull he trigger if they would confirm black on white (in this way You have a prove if something =)

[fatrobotsneedlove]

Thanks for the advice, man. I appreciate the help. I'll get this figured out.

Then finally get to rendering