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[afo]

It is possible to connect the board to a different power supply?

Hi all,

First, please apologize me if I am making a very stupid question or this is the wrong forum to ask for.

My question is: If I connect the power connectors of a HD5970 to an independant PSU; I switch on that PSU, and then I power up the PSU of the motherboard where the card is; Could something be damaged (provide that the ground level is the same in both PSU by connecting the ground cables together)? And if I invert the power up sequence (first motherboard, then card)? Thanks in advance for any insight about this.

best regards,

Alfonso

[eklund_n]

I guess you do this because you think that your ordinary PSU isn't strong enough or have not enough PCIe-power connectors.

It should be fine as long as both PSU are powered on when you start the computer. Pic: http://www.vistax64.com/attachments/graphic-cards/14507-ati-crossfire-curiosity-4890cf.jpg

[afo]

Thanks for the answer! Yes, you are right, I don't have enough power in the mainboards's power supply, so I am exploring if I can use a power supply just for the HD5970 boards.

By the way, what is exactly "...both PSU are powered on when you start the computer"? What could be an acceptable delay between the motherboard psu and the hd5970 psu? 1ms? 100ms? no more than 1 sec? It is possible to turn on two psu when you start the computer? Is there a link explaining how to do that? Thanks in advance for the information.

best regards,

Alfonso

[cjang]

If possible, it will likely be easier to just get a larger PSU. I'd be afraid of latch-up issues (http://en.wikipedia.org/wiki/Latchup) caused by multiple positive voltage rails. When there are multiple PSUs in a system, if the design isn't right, there is a "race condition" during power-up. A system might work or might not depending on the timing between the PSUs.

I'm not really knowledgeable about this in the context of a PC. My personal experience is with a small embedded computer and some supporting ICs and discretes. However, it is another failure mode for your system if you use multiple PSUs. Definitely do some more research (as you are doing).

[nou]

i have seen some multy GPU system where one 1kW PUS wasn't enough. but buy stronger PSU is better option.

IMHO you should start first GPU PSU and then motheboard PSU.

[afo]

Again, thanks for the answers.

I am doing some research, but I couldn't find something useful and I think that it's not a good idea to try and see what happens.

I also think that I should start GPU PSU first; but I guess that hd boards like hd5970 have an internal power up sequence and internal boot process, so I would like to know what happens when they are powered by their power connectors but there are no pcie bus available or the pcie bus is available some time later; how will this affect the boot sequence of the board? It would be great if someone from amd answers that...

best regards,

Alfonso

[eklund_n]

the important thing is that both PSU are on when you press the start button of the computer.

1) remove the power cords of both PSU, connect all connectors as you want them.
2) attach the power cords and flip on the switches on the backside of the PSU (if there are any)
3) done. start the computer when you need it.

the only thing that can be a problem is if the second PSU only delivers on the 12 V rails when the ATX-connector is attached. i.e. it senses if it is connected to a motherboard. measure this with multimeter when not connected to a motherboard or just connect a single fan on 12 V to see if it starts spinning. good luck!