Does having three PSU 19A rails mean I can't run a 24A GPU?

[MikeRossyBoy]

*I tried to look for a PSU sub-forum but I couldn't see one so I put it here*

I recently upgraded from a ATI 4670 to a nVidia 460 (768MB) running it on my 620w CoolerMaster PSU.

Since installing the 460 it would crash in pretty much every game, but when i tested Furmark (albeit for two minutes) it was fine. I thought my PSU would be fine but I had a look at the box and it only has three 12v rails giving 19A of current while the 460 recommends 24A of current to work.

Is this why the 460 was flakey in performance as from what I understand a PSU doesnt split rails etc

I looked in the instruction book but it doesnt mention what rail does what.

 

[kitch9]

Without looking at the instructions I would guess you could use a different rail for each power socket on the card and you'd be fine.

 

[Final8y]

Without looking at the instructions I would guess you could use a different rail for each power socket on the card and you'd be fine.

+1
Assuming that the 2 PCI-E 6 Pin connectors are on the same rail then maybe try a Peripheral molex to pci-e power cable to power one of the gfx cards sockets.

 

[MikeRossyBoy]

Thanks for the replys Final8y and kitch9 but while I thought about it the card pulls 75w from the mainboard and the two pci-e connectors then supply 75w each so its unlikely that all the 24A will all come from the third rail for example.

The instruction book says the first and second rail operates half the 8 pin CPU connector each and the second rail operates the 24 pin ATX connector, so im guessing it must come from different rails.

If only I hadnt seen that XFX 'one rail is better than two' stuff on their website!

 

[Greebo]

I hate split rail psus and my last three have all been single rail. Much easier and better IMO.

 

[JTrickle]

Where did the 24A figure come from?

19A x 12V = 228W.

The Nvidia 460 is a 160W card. Factory overclocked cards might use a touch more, but you would have to fully overclock it to hit 228.

Use two different rail power plugs anyway.

 

[Vince]

Im running a q6600@3ghz and a 5850 @ 1000/1250 on a 460 coolermaster with 2x18a rails. I don't think its the psu, what board etc are you using (edit: sorry didn't see sig..)? have you tried setting the system back to stock and testing?

Sometimes changing gfx cards will effect your max cpu overclock.

 

[HangTime]

I used to have a Quad 25A rail PSU and it was a nightmare, simply wasn't up to the task of running my GTX280. Much better with a single 60A rail.

 

[Dutch Guy]

The recommended 24A is for the total 12V rails, if you have three 19A rails it means that (theoretically) you can get 228W from each.

What you need to try to avoid is putting more than one component on one rail so that you split the power over all three rails.

 

[drunkenmaster]

Where did the 24A figure come from?

19A x 12V = 228W.

The Nvidia 460 is a 160W card. Factory overclocked cards might use a touch more, but you would have to fully overclock it to hit 228.

Use two different rail power plugs anyway.

Its worth pointing out that the factory overclocked cards with increase voltage can use significantly more than 160W, but if you up the voltage/overclock on your own you can push to 470gtx power levels, and beyond. They scale up in power very quickly when you bump the voltage.

Almost all psu's only have one rail, its just one rail split into various over current protected rails.

There was a short while everyone thought multiple rails were better, then after a couple years people started thinking a single massive rail was better, in reality, neither is true though I forget the reasoning these days.

THe only real issue is on the more complicated psu/rail setups splitting the power of a few high power devices can become a little problematic.

Most of the issue was safety though, you aren't supposed to push more than 18amps down any one rail, or that was a safety standard that was introduced that started the multiple rail thing.

Probably more than anything else its a marketing gimmick, have a reason back then people needed a new multirail psu, then a few years later everyone is persuaded they need a single rail psu, then a few more years later everyone is told they need a high quality multi rail psu. In 5 years we'll be convinced we need 4 small separate 200W psu's as it gives cleaner power.

Anyway the only thing I can see on Nvidia.com regarding the 460W is a recommendation you have a 450W PSU at least, nothing more or less.

It will likely draw 40W or so from the pci-e slot and the rest from the pci-e power connectors, in a thread elsewhere we were talking about how it decides where to draw power from, xbitlabs have a 480gtx review where they've added power/load monitor between the pci-e slot and gpu and the power connectors and seen it tends to maintain a level load between sources. IE rather than 100% from the slot, 100% from one connector and 20% from the next, it seems to take around 60-70% of the maximum from each source.

As long as the op uses a pci-e connector thats supposed to be on the 3rd rail, there won't be an issue.

 

[JTrickle]

I rekon my version you quoted was more succinct