Topic: Using 2 Psus (Read 1755 times)

If you use the Powered USB riser, which does not draw from the PCIE slot, you can connect the power to the 2nd PSU.

Just luck. No I haven't had personal experience but I have been mining for more than a year now and when I started out, a friend of mine was also starting out - but he is an electronics engineer. I work for an engineering company as a technician.

He explained to me why you must use the 2nd (slave) PSU for ONLY 6/8 pin GPU power connections. To be honest I didn't completely understand what he told me but he drew me a simple circuit diagram and showed me how the two PSUs can "fight" each other over the 12v level - especially depending on whether they have a common ground/earth or not. The motherboard, and risers connected to them must all use the same 12v source. If there is a difference between them (and switch-mode PSUs like you get in computers are always fluctuating a little) then they are both trying to "correct" the voltage so they are the same, and in some circumstances this can cause problems, and in a few cases make stuff burn. I was lucky because I had someone who understands electrical and electronic things better than me - I do understand how it seems logical to power a GPU and the riser that connects it to the motherboard with the same GPU, but it's wrong electrically. My understanding of this might be technically imperfect but it was explained to me by someone who has worked as an electronics engnineer for more than 20 years, so it's my simplified translation of his advice.

Like I said - I have been mining for more than a year and I spent a long time posting on the Ethereum community mining forum (until it became pretty much just a place where noobs would fight over the best BIOS mod for an RX480). During that time I saw quite a few pictures and read descriptions of people who had burnt or melted molex connectors, SATA power connectors and PCIe 6/8 pin connectors. Many of them (not all but most) were caused by the incorrrect usage of a 2nd or even 3rd PSU.

Since most miners use fairly good quality PSUs that have good stable 12v output, many people can get away with doing it wrong, but if you have a problem with 1 of them and the 12v output fluctuates too much - stuff can and will burn or melt.

If I understand what you are saying, then I disagree.  I have multiple rigs, all have 2 PSUs.  One PSU powers both motherboard power connections (24 pin and 6/8 pin), the SSD, and will typically provide power to one or two GPUs (both the 8-pin power connection AND the Molex/Sata adapter connection to the bottom of the riser card).  The other PSU supplies power to the other 4/5 GPUs, both at the 8-pin power connection AND to the card's Molex/Sata adapter.

No issues whatsoever.  Just luck on my part?  Did you ever personally experience any issues by connecting the 2nd PSU to the riser boards (not just the 8-pin GPU power connection)?

I'll be using all 2x750w in open frames and 1600w in closed cases. All evga Titanium using 220v. Its hard to beat 96% efficiency.

I think it will be easier to resell a 750 vs a 1600.

Thanks for all the input guys

What happens if the main PSU turns off and the slave PSU still being active and giving 12v to the GPUs? can this harm the GPU's ?

No offense - but you gave some terrible (and potentially dangerous) advice here.

It is VERY important that the PSU that powers the motherboard/cpu/ssd, etc is also the one that powers ALL the risers! Otherwise you can get problems where the two PSUs are kind of fighting each other to maintain whatever is the proper 12v reference to ground.

So in any two PSU system, the "master" PSU powers the motherboard/cpu/periferals + always the first GPU in the primary PCIe slot and then as many more GPUs as you are confident it can handle + ALL THE POWER TO ALL THE RISERS.

The 2nd or "slave" PSU just provides the 6/8 pin PCIe power to whatever extra GPUs the "master" isn't powering. Definitely not any power to risers or in fact anything other than 12v PCIe GPU power plugs.

To jump the 2nd PSU simply short the green and any ground (black) wires on your 24pin connector. I just use a paperclip.

before changing everything let's jump to the first PSU.

and therefore start from the beginning would be advantageous to the fore.

It's actually very simple

https://forum.overclock3d.net/showthread.php?t=394

I can attest that this method works too, but some may argue that it is slightly dangerous because the 2 PSUs wont share a common ground. I've use both add2psus and just manually jumping the slave PSUs, both worked fine with no issues.

Usually the fans keep spinning but it should not really hurt anything.  That add2psu is more for farms I think so they can be certain the power is completely shutoff when they remote in and shutdown but wont be able to service the rack for sometime.

Imo your rigs should be on more than off.

Can you please explain how you make/use a jumper.
Total greenhorn here

Just use jumper on secondary Psu, dont buy that add2psu,

have 6 rigs running with jumper on every Psu that dont feed motherboard.

Before you turn everything on, just turn jumped Psus first, them start mother board

Profit

How would one go about things without add2psu?
Would it hurt GPUs if one PSU would be constantly on while the other would power up system and the rest of GPUs?

<