Do I need Powered Risers?

[sitefive]

do you need them to be powered as well when its X16 to X16?
I believe that you need them to be powered when its from x1 to x16 but what about just with the x16 to x16 ?

[atp1916]

Hey bud,
You need powered risers when you are dealing with big TDP cards like 7870s, 79xx's, R9 290x.  Needing them technically has nothing to do whether it is a x1-x16, or x16-x16 etc cable.

The manufacturers always estimate card wattage based on the assumption that the 75w provided by the PCI-E bus will be provided by the physical bus connection.

If you got a heavy hitter like say a 7950 or R9 290 hooked up, the card will be drawing that extra 75w through the pcie pins, overspeccing those pins and that entire cable/connection.  In other words, you risk blowing something up because your pcie pins are pulling so much extra.

On a lesser TDP card like a 7850 or a R9 270, you're mostly ok.

[Colin Miner]

do you need them to be powered as well when its X16 to X16?
I believe that you need them to be powered when its from x1 to x16 but what about just with the x16 to x16 ?

But the difference in cost between powered and unpowered, I would opt for powered for the 'safety factor'.

[sitefive]

Should I be fine with using 2X 6970 cards with x16 to x16 unpowered risers, 1X 5850 card straight plugged in board and 2X 6970 cards using x1 to x16 powered risers?

[atp1916]

6970s are solid 220-250w units... You would be safe running them on non-powered until you get some powered.  

I would not run them forever on non-powered risers, no.

[cthulu1]

To explain to people why you need powered riser cables:

MOBO PCI-E can only pull so many volts from the ports. this is not a problem when there are only a few devices linked up through these ports. however, if at any time the amount of energy being pulled through these ports goes over the maximum output (i.e. 4 video cards and a shitty PSU), then the linked hardware will fail. in order to curtail this, a powered riser provides the additional voltage through the MOLEX connection. modding unpowered riser cables to powered ones is relatively straight forward if you know what you're doing.

hope this helps. :]

[Bfljosh]

I' m running 4 x msi twin frozer 7950 slightly overclocked cards per rig on a gigabyte 990fx ud3 motherboard with a 1250 watt seasonic psu. No powered risers, only unpowered 16 x 16 risers. No problems.

[cthulu1]

running 4 7950 slightly overclocked cards per rig with a 1250 watt seasonic psu. No powered risers, only unpowered 16 x 16 risers. No problems.

just to clarify, what may be true for this gentleman may not be true for you. instead of using the motherboard power supply, the powered cables have an additional MOLEX connector to plug into the cable thereby directly supplying the 12 volt line, which in turn does not consume power from the motherboard - as long as the cable is made correctly and the 12 volt lines are properly connected.