SATA->molex adapters for 16x->16x risers

[coinpops]

Hello, I'm currently mining with two RX 480s, hoping to add two RX580s to the same rig.

I purchased two powered 1x->16x risers and two powered 16x->16x risers. The two 1x->16x risers came with SATA->molex adapters, which I've read is a big no-no for 1x->16x because SATA can't handle the power draw.

But would I be able to use the SATA->molex for the 16x->16x risers? The reason I ask is that the 16x->16x risers look like this where 2 of the molex pins aren't even used, so I assumed that riser would be using less power. In fact, I've seen unpowered 16x->16x risers too -- do I even need to power mine at all?

Ideally I'd just use molex straight from my PSU, but I only have 3 open molex connections (and they're all on the same cable). My plan is to power the 1x->16x risers directly from the PSU molex, but not sure if I can power the 16x->16x risers differently (if they even need to be powered at all). Thanks.

[MATHReX]

According to my experience, I've been using SATA to power three 1x to 16x USB risers and I haven't bumped into any power issues, moreover, the cables are running pretty cool.  Can you provide me with the info on where you found that powering 1x to 16x USB risers is not a good idea as they cannot handle that much power draw?

[iamnoobplzhelp]

See this site for reference:
http://www.playtool.com/pages/psuconnectors/connectors.html

Here's where you may run into trouble:
A 6 Pin GPU power can provide 75w to the card.
An 8 pin can provide 150w to the card

Any additional power your card may be taking comes from the motherboard (or riser).

SATA adapters can deliver 22-60w (Depending on what rail it's connected to)
Molex adapters can deliver 14-54w (Depending on what rail it's connected to)

So, if your card is pulling 150w, and it has a 6 pin connector, it's going to be pulling the rest of the 75w from the riser. If it's not properly powered, you riser cables will burn out.

If you're running properly undervolted and your cards are pulling less than 100w, then it shouldn't be a problem.

The safest thing to do is to use the 6-pin powered risers like this:
http://www.parallelminer.com/product/ithoo-usb3-0-pci-express-1x-to-16x-extender-riser-card-adapter-w-24-cable/


And then use a splitter like this:
http://www.parallelminer.com/product/18awg-pci-e-6pin-to-dual-8-pin-y-splitter-extension-cable-2x-62pin-cable-6in-each-side/

The power going to the card can go into the riser and the card. The cables themselves can handle way more than 75w/150w.

If you absolutely must use the SATA/Molex risers, make sure NOT to daisy chain them. Plug in as many independent cables as possible. 1 per riser is ideal.

[coinpops]

Thanks for the responses!

I found a very good thread here that also strongly suggests avoiding SATA->molex adapters along with appropriate workarounds (Zorg33's comments are particularly helpful).

As for my particular issue, turns out the powered 16x->16x risers I bought were complete garbage, and neither of them work. I decided to grab one of these, which is rather expensive, but working well so far. I intentionally bought an unpowered riser so the power would be drawn from the mobo and I wouldn't need a 3rd molex connection. So that leaves me with 1 GPU plugged directly into the mobo, 1 GPU on the unpowered 16x->16x riser, and the other 2 GPUs on the 1x->16x USB molex-powered risers. Things have been stable so far, and from what I've read, this setup should be relatively safe.