GPU and PSU

[JambonBeurre]

Hi all,

I finally got my hands on 3080, and after all that effort, the idea of whether my PSU is good enough or not was totally forgotten until I got the card in my hands.

I have read, the 3080 manual, countless threads and answers on the situation, and the general consensus is each 8pin connector on the gpu side should be plug on a separate 8pin connector on the PSU side.

I'd like to run my 5700 (for mining) and the 3080 (for gaming) in the same pc, but found out I'm limited to only two 8pin connectors on my PSU. I have put below a quick sketch showing different setup options:

Option 1 is my current setup. Although it is working fine, the 3080 is not plugged as it is recommended. Only one cable from the psu splitting in two 8pin for the 3080. So higher load on the cables. The 5700 is also plugged on one cable splitting in two, but the 5700 only draws 100watts while mining so all good.

Option 2 is an idea that popped up last night, and the reason of this thread! In that scenario the 3080 is plugged on two different power cable (as per the recommendation), then the 5700 is plugged with the spare 8pins that runs off those two cables. So effectively daisy chaining the 5700. As the 5700 only draws 100watts while mining, that's only 50 watts per connector for the 5700 (or less if considering pcie providing up to 75watts of power). My reasoning behind this, is the power going through those cables will be better split, reducing strain on the cables. Power wise, this should be all good, cable and connectors should be able to withstand safely the power. Although the idea seems perfect, I don't know how good of an idea this is? As I have not found anything on the net about it. Would one GPU affect badly the other, because they share the same cables? Was hoping someone here could shed some light on this

Option 3, is of course the ideal setup. But this setup requires me buying a new psu, as I do not have enough 8pin connectors on the psu. (only have two and would need at least three).

Thanks for reading, and all answers are appreciated

 

[Jay85]

New psu, i wouldn't risk it with how difficult it is to get cards still.

Get an appropriate psu that can handle it and has the correct amount of connectors.

 

[JambonBeurre]

I thought so. But figured I'd ask.

Out of interest though, say you had much less power hungry cards (say <150/170watts), what I've put down as Option 2 (or daisy chaining cards on a single cable) would that be possible, in theory? As I've never came across that setup before, and doesn't seem to be mentioned anywhere. And no warning signs on this in psu or gpu manuals. Just curious to know if that can affect performance in any sort of ways or be detrimental for graphic cards no matter the power of them.

 

[pastymuncher]

What make and model is the psu? It is highly unusual for a modern psu to only have a pair of 8 pin pci-e connectors, they usually have connectors made up of 6+2 pin pci-e cables and the 8 pin cables are usually the EPS 12v.

 

[JambonBeurre]

It's a 750w Super Flower Leadex III. Yes sorry for the confusion, there's two pcie cables provided with the PSU. which are one 8pin on the PSU side and two 6+2pin on the pcie side. I only mentioned 8pin in my post above, just to simplify, but they are indeed 6+2 connectors.

In the end, I did take the gamble to power the 3080 with two cables, then daisy chain the 5700 off the two spare 6+2 connectors, as shown as option 2 in my sketch. After some testing last night, seems to run very well. No stability issues or unusual things happening.

When mining, the 3080 pulls about 240watts and the RX5700 100watts. So a total of 340watts shared over the two cables. No issues at all. However, when gaming the 3080 pulls 320watts (not overclocked).

So when playing games, I just stop mining on the 5700 and let it cool down, as that would bring the total power to 420watts and would be afraid to get too close to the PSU limits as my Ryzen 5 3600 is also overclocked.

I'll keep a close eye on the pc for the next week or two, to be sure everything is running well.