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Discussion Starter #1
im just wondering about power requirements of gpus and riser cards etc. i need some clarification on how to work it out please

i.e my 1080ti is about 240watts. but as the pcie slot can provide (75w) does that mean its only drawing 165w(240w-75w) from the two 8-pin connectors?

however...... as it will be in a 1x-16x pcie riser card, powered by a sata/molex/6-pin cable. is the mobo pci slot no longer providing the (75w)power to the gpu, and its all coming from the powered riser cards slot?

i currently have a gtx770 and a 970 plugged into two risers cards but as i say above i will be adding my 1080ti to it, and possibly removing the 770 and adding two more 970's (when they arrive)

which means adding a psu splitter and another power supply, so im wondering how to balance out the loads between the two psu's cables.


thanks in advance for the help
jim
 

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All you should be worrying about is total PSU capacity. What PSU do you currently have? The risers shouldn't really matter from what I understand.

I'd be looking at having a total of 900W+, that will be enough to run all 3 cards.
 

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All you should be worrying about is total PSU capacity. What PSU do you currently have? The risers shouldn't really matter from what I understand.

I'd be looking at having a total of 900W+, that will be enough to run all 3 cards.
Incorrect.

The risers (and how they are configured) are important here. If configured incorrectly you can have a fire.

Jimmy, you are correct that the motherboard will no longer supply the power - all pcie power will be supplied by the risers. You should strive to power the risers with molex or pcie connectors, as sata connectors are not rated for 75W. With molex, you should strive to only use a single molex per PSU cable to stay within spec.

If you have to do sata, never do it with an adapter as molded sata adapters are rated for even less current than a proper sata power cable from a power supply. The molded sata adapters included with most risers are just begging for trouble, and you'll see some mining rigs have caught fire because of them.


As far as balancing the loads, the benefit of the riser is you're electrically no longer drawing power from the pcie slot. Best practice is to make sure the riser and the GPU are both powered by the same power supply, and preferably the same rail. Which supply you use for which cards and the motherboard will depend on the size of the supplies and the GPUs themselves.
 

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Discussion Starter #4
thanks for the info.

im currently using a gm700 (gamemax psu) its currently running the 770 (230w) and the 970 (145w) fine on the risers. so i figure the straight swap of the 770 for the 1080ti will go ok.

but for adding another two gtx970s im guessing ill need at least another 500watt power supply.......or one with at least 300wats on the 12v rail.

ill let you all know how it goes

thanks again
jim
 
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