2 PSUs and Powered Risers: No Consistent Answer? Looking for HF expertise.

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It seems as though there are two schools of thought on the question of "which PSU should power each riser?" I spent a few hours researching multiple forums and posts, both here and on other mining forums. The advice being given is not consistent and seems to fall within one of two completely different approaches. I am not knocking anyone who has given advice on this topic -- I am just confused as to which is the right answer. The reality is that both approaches likely work for some people, else there wouldn't be such a divide. For reference, here are a few examples where it's clear there isn't a consensus in the thread:
https://litecointalk.org/index.php?topic=6171.0
https://litecointalk.org/index.php?topic=14758.0

As an additional question, also hearing mixed messages on whether or not the USB risers are safer because there is supposedly no power connection at the PCI-e point and "it's just a data connection to the motherboard" and the molex handles 100% of the power affiliation. I don't know if this is true or not, and how it might affect the overall answer of wiring approach.

I bricked two motherboards last night because I either screwed up, or had faulty equipment. I'm still not sure. But I want to get it right when I try again. A picture paints a thousand words, so I would love your comments and expertise as it relates to these scenarios. I'm fairly new to HF and have been impressed with the knowledge here - don't let me down :)

Note: my situation is a bit unique because I'm introducing a 2nd motherboard to take advantage of an additional PCI-e slot (just onboard right now, and can potentially add an additional riser to this 2nd mobo). I would think removing mobo2 and the 6950 directly seated on mobo2 from the equation would get you to a more familiar scenario but I wouldn't think it would change the answer, or would it?

Thank you in advance for all your help and responses.

riserq.jpg
 
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Conventional wisdom is Option B. Have all of the power to each card come from a single power source.
 
oblox said:
B but remove mobo 2.
Click to expand...

Would mobo2 cause a power issue?

I'm just going to get a 6 PCI-e board next time, but I still want to try and understand what went wrong for me. Had the two boards for a total of 7 potential PCI-e slots that I wanted to use. Got the 750 and 700 watt PSUs and figured as a whole, that would be enough power to run the 7 cards on the total 7 PCI-e slots...but I don't know if it's the mobo2 that would have caused both mobos to die on me.

Thanks for the info.
 
Thanks for your responses so far -- out of the 3 posts, it sounds like 2 are wiring one way, and another is wiring the other way. So I think both CAN work.. but is one better than the other when using the USB risers? Since there's no power heading back into the motherboard via these risers (supposedly), maybe either is fine. Just don't want to brick another board!
 
If you use USB risers then you would power the motherboard/ hard drive/ accessories with that power supply and any video cards that fit within the power threshold. The second PSU can power any other video cards risers and their PCI-e slots.

Again this is using USB risers as they do not share power back to the motherboard. It is suggested that with USB risers power both the risers and PCI-e slots with the same PSU from all the reading I have found.


You could technically also power all PCI-e Risers with the PSU hooked up to the motherboard and all PCI-e with the secondary PSU. This method is recommended when you are using the ribbon risers.
 
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I run 2 PSUs for different GPUs and I always follow the rule to power the GPUs in every way by the same PS. PSUs can't "talk" to each other so if 2 are feeding the same card, you could end up in all sorts of bad.
 
96redformula said:
If you use USB risers then you would power the motherboard/ hard drive/ accessories with that power supply and any video cards that fit within the power threshold. The second PSU can power any other video cards risers and their PCI-e slots.

Again this is using USB risers as they do not share power back to the motherboard. It is suggested that with USB risers power both the risers and PCI-e slots with the same PSU from all the reading I have found.
Click to expand...

Thanks! I think that's the direction I'll go. Thinking of going with the Asrock BTC board.


edge929 said:
I run 2 PSUs for different GPUs and I always follow the rule to power the GPUs in every way by the same PS. PSUs can't "talk" to each other so if 2 are feeding the same card, you could end up in all sorts of bad.
Click to expand...

Thanks for the input -- it's funny, I read that (1) the 6/8pin GPU connections never have anything to do with the aux power that the riser would provide, so it doesn't matter if they're different, and they never talk to each other.... and (2) if the GPU doesn't get enough power from the 6/8 pin connectors, it looks for it from the riser power (mobo if non-powered, or molex if powered), so if that's true, #1 can't be true. Guessing #1 is false.
 
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