Be Queit! PSU - run at multi rail or single rail

[davidst99]

Hi, I'm a buying a 850W Be Quiet! PSU. It allow you to chose between a multi rail or signal rail setup? I have a I7 4790K, GTX 980 TI (will eventually buy another one) and 4 hard drives. Should I run it at multi rail setup or signal rail setup? My 1050W Seasonic PSU that went bad I think ran at signal rail. Do you know what type of rail setup I should set the Be Quiet! PSU? If I run it at multi rail do I have to pay attention to what port I plug in the cables to on the PSU? I'm a newbie when it comes to PSUs. Thanks.

David

 

[Smoblikat]

Personally I prefer single rail PSU's. But for your setup, it shouldnt matter too much. All the connectors should already be setup on the appropriate rails, so you can just plug them in and not worry about it too much. I think most modern multi rail PSU's are setup like that.

 

[lehtv]

Very few setups care whether the unit is single (note: not 'signal') or multi rail. A properly specced multi rail unit has enough amps per rail so that accidentally pulling too much power from a rail is a non-issue. You'll sooner run into the total wattage limit (overpower protection) than overload any single rail.

If the unit you're considering is Dark Power Pro P11 850W (far as I know, other 850W Be Quiet! units are discontinued), then you've got four +12V rails of which two are rated 30A (= 360W), and the other two 35A (= 420W). This is a lot of power per rail for a unit this size - which is good. According to Tom's, power distribution is as follows:

Which means you have 360W for the motherboard, drives, etc., 360W for the CPU, and 420W for each graphics card. 980 Ti uses around 250W which is only 60% of the available power on the rail.

The point of the unit's optional single rail mode is that it "eliminates any problems that may arise from triggering overcurrent protection (OCP) once you begin overclocking power-hungry graphics cards" (Tom's). Technically, however, if you wanted to run a single card overclocked to near 420W, you could just use one connector from each rail and avoid that issue; and if you wanted to run two such cards, you should be running a 1200W unit, not an 850W one.