Confused about +12V rails

dyst0pia · Feb 4, 2009

I have a ThermalTake W0106RU (specs here), and I'm really confused about how the four +12V rails work. The specs say they are rated for 18A, with a combined loading of 56A. Does this mean I can only provide 36A to my graphics card, or 56A, or only 18A?

I want to swap my graphics card out for a GTX 285; will this be enough power? Specs say they need 40A on the +12V rail. As my sig says, I'm currently using a GTX 260 with no problems, which is supposed to need 36A.

On that note, my power supply has 2 ports for 6-pin PCI-E power, and one fixed cable for 8-pin PCI-E power. Which ones should I be using with my GTX 260 (I have an 8-pin to 6-pin adapter)? If I do upgrade, should I use the fixed cable, or find a 6-pin to 8-pin adapter and use the two PCI-E power ports?

Thanks

wingman99 · Feb 7, 2009

It will work fine you have plenty of power. :clap:

dyst0pia · Feb 7, 2009

wingman99 said:
It will work fine you have plenty of power.

Thanks for the info. I've thought about it a little more, and I think I'd rather have a 295. That's really pushing it, though, isn't it? 680 watts recommended, with 46A at +12V. Do you think that'll still be okay? Or should I just invest in a new power supply?

wingman99 · Feb 7, 2009

dyst0pia said:
Thanks for the info. I've thought about it a little more, and I think I'd rather have a 295. That's really pushing it, though, isn't it? 680 watts recommended, with 46A at +12V. Do you think that'll still be okay? Or should I just invest in a new power supply?

You are still fine your psu is +12v 18A x 4= 72A pleanty of power.

I can run that 295 on my corsair HX 620w

Corsair tech http://houseofhelp.com/forums/showthread.php?t=75572

JumpingPerson · Feb 7, 2009

You should familiarize yourself with which power connectors are attached to which rails, as your PSU will surely have several 12v connectors to each channel.

Your ATX 24 motherboard power can deliver ±6a to the gpu on one 12v rail. The GPU will probably also have 2 power connectors (a 6 and an 8 pin if you are using the 295.) Supposedly the 6 and 8 pin connectors can deliver identical power (at least 14a) as the 8 pin was only designed to make sure a fool doesn't plug a high wattage card into an insufficient PSU. So you can only give 18a to the card if all three of those connectors are on the same rail, but if you check with your power supply, you can theoretically connect 3 18a rails to your GPU. 2 rails Should probably be sufficient.

Also on the 295, I think the mobo can only help power one of the GPUs, so the other one has to get its full 10a or so from an 8 pin connector (and a single rail.)

Also your Thermaltake unit can power the 295
and wait for confirmation from a genuine Electronics expert before you believe anything I wrote

Out of curiosity I looked up some Info on the Thermaltake Unit and it looks like it doesn't have 8 pin graphics power
the 8 pin connector on it is for CPU power

wingman99 · Feb 7, 2009

GTX 295 requires a 22A rail minimum to run properly, you only need the two 18A PCI-e conectors from your PSU = 36A pleanty left over.

Madnyss · Feb 7, 2009

wingman99 said:
You are still fine your psu is +12v 18A x 4= 72A

While all the 12v Rails can provide up to 18A each Rail, that's the max across all Rails and is usually lower than that. On the Thermaltake its max across all Rails is 56A not 72A.

That Thermaltake is not a multi Rail PSU. It has 1 single Rail that is divided up with OCP ( Over Current Protection ). If any Rail Draws more current than is allowed by OCP it shuts off. Most multi Rail PSUs are not "REAL" multi Rail.

PCI-E 1.0 Can supply up to 75W
PCI-E 2.0 Can supply up to 150W
6pin PCI-E Can supply up to 75W
8pin PCI-E Can supply up to 150W

A GTX285 is PCI-E 2.0 and has 2 6pin PCI-E Connector so it cannot draw more than 300W. On the Nvidia Page it says a Stock Clocked GTX285 will use 183W of power or 15.25A.

That PSU will run a GTX285. If you have troubles with it, make sure you don't have to much hooked up to each rail.

JumpingPerson · Feb 7, 2009

Madnyss said:
6pin PCI-E Can supply up to 75W
8pin PCI-E Can supply up to 150W

These are the official numbers but they are conservative and inaccurate.
8 pin power cannot deliver more power than 6pin, and only contains more 12v returns (for making sure the PSU is sufficient.)

dyst0pia · Feb 8, 2009

JumpingPerson said:
You should familiarize yourself with which power connectors are attached to which rails, as your PSU will surely have several 12v connectors to each channel.

Your ATX 24 motherboard power can deliver ±6a to the gpu on one 12v rail. The GPU will probably also have 2 power connectors (a 6 and an 8 pin if you are using the 295.) Supposedly the 6 and 8 pin connectors can deliver identical power (at least 14a) as the 8 pin was only designed to make sure a fool doesn't plug a high wattage card into an insufficient PSU. So you can only give 18a to the card if all three of those connectors are on the same rail, but if you check with your power supply, you can theoretically connect 3 18a rails to your GPU. 2 rails Should probably be sufficient.

Also on the 295, I think the mobo can only help power one of the GPUs, so the other one has to get its full 10a or so from an 8 pin connector (and a single rail.)

Also your Thermaltake unit can power the 295
and wait for confirmation from a genuine Electronics expert before you believe anything I wrote

Out of curiosity I looked up some Info on the Thermaltake Unit and it looks like it doesn't have 8 pin graphics power
the 8 pin connector on it is for CPU power

It's this one. The newer revisions (one of which I have) have an 8-pin PCI-E connector. I can't get confirmation on this, but it looks like the two modular 6-pin PCI-E are on their own 12V rail. Unfortunately, it looks like the 8-pin PCI-E are on the same rail as the 24-pin ATX power.

If the 8-pin's supposed to be fully loaded with the 295, this may pose a problem. I've got 18A to play with on the 6-pin, but probably a lot less than that on the rail with the 8-pin. Would it be smart to get a 6-to-8-pin adapter to push that other connector to the 6-pin modular output?

Also, what would happen if I overload the current protection on one of the rails? Does the power supply just turn off (which is okay)? Or is it going to do something stupid like explode or experience some other cataclysmic event (not so okay)?

And thanks for the correction; I'm using "rail" to mean each current-protected line split off from the single real 12V rail.

Edit: Oh, one more thing. My motherboard has a 4-pin molex connector near the PCI-E bus. What's up with that? I've just had it plugged in anyways, but I don't really know what it's for. FYI, I believe the molex and SATA power are on rail +12V4 by themselves.

JumpingPerson · Feb 8, 2009

dyst0pia said:
Unfortunately, it looks like the 8-pin PCI-E are on the same rail as the 24-pin ATX power . . . Would it be smart to get a 6-to-8-pin adapter to push that other connector to the 6-pin modular output?

I think thats a good idea. It seems strange the 8 pin pcie would be on the same rail as the atx power. Also don't believe by the false 75w ceiling of the 6 pin connector.

dyst0pia said:
Also, what would happen if I overload the current protection on one of the rails? Does the power supply just turn off (which is okay)? Or is it going to do something stupid like explode or experience some other cataclysmic event (not so okay)?

I am also curious as to the answer of this question. I think the PSU would probably operate at maximum current it allows for that rail and the device would experience instabilities?

dyst0pia said:
My motherboard has a 4-pin molex connector near the PCI-E bus. What's up with that? I've just had it plugged in anyways, but I don't really know what it's for.

I think these are backup power in case you have many expansion cards, but unfortunately it can't increase the power of the pcie bus. It is only useful if you are using SLI/Crossfire with a multi-card setup. I think. Can't hurt to plug it in I guess?

Oklahoma Wolf · Feb 8, 2009

dyst0pia said:
Also, what would happen if I overload the current protection on one of the rails? Does the power supply just turn off

Yes.

JamesXP · Feb 8, 2009

I beleive the Molex by the PCI-e slot is to allow more current through the PCI-e slot.

AlabamaCajun · Feb 8, 2009

Your specs are close to what I had on my (sold) Q6660 system with the OCX Stealth 500 with no problems oced to 3.3G and one 3850 fanless ATI card, 2 drives + 1 optical and 4 fans. I was able to keep the vcore at 1.325V which helped a lot.

I now prefer the single rail cosairs which even the 400CX would run my rig due to the low power drive and video card. Watch for sales on the Corsairs and start with a 550 or better.

wingman99 · Feb 8, 2009

dyst0pia said:
If the 8-pin's supposed to be fully loaded with the 295, this may pose a problem. I've got 18A to play with on the 6-pin, but probably a lot less than that on the rail with the 8-pin. Would it be smart to get a 6-to-8-pin adapter to push that other connector to the 6-pin modular output?

You have plenty your 6 pin and 8 pin have 12v 18amp each that's why they have a red plug on them that go into the red power supply conector.

6 pin = 18A = 216 watts

8 pin = 18A = 216 watts

Madnyss · Feb 8, 2009

JumpingPerson said:
These are the official numbers but they are conservative and inaccurate.
8 pin power cannot deliver more power than 6pin, and only contains more 12v returns (for making sure the PSU is sufficient.)

JumpingPerson said:
I think thats a good idea. It seems strange the 8 pin pcie would be on the same rail as the atx power. Also don't believe by the false 75w ceiling of the 6 pin connector.

PCI-E 8 pin is not implement as stated by the Standard. There is only suppose to be one extra ground wire and 1 sense wire, PSU manufacturers have just added an extra ground instead of the sense wire to trick the cards into thinking they are working correctly. If they were to add the sense wire it would increase the cost of a PSU. In a DC circuit you can supply more power by adding ground wires but two extra grounds won't double the current.

75W is the standard. If a company say that it supports 6pin PCI-E connector then they are complying with the Spec. Yes the connector can draw more than 75W but anything greater than 75W falls outside the Spec and cannot be called 6pin PCI-E compatible. The PCI-E slot on the Mobo can also supply more than 75W/150W but 75W/150W is the standard and anything that exceeds it is not covered.

As with OCP it will just shut off. Your PSU will handle a 295, you may just have to try the connectors the other way if you experience random shut downs. None of this will harm your PC.

Confused about +12V rails

dyst0pia

Member

wingman99

Member

dyst0pia

Member

wingman99

Member

JumpingPerson

Registered

wingman99

Member

Madnyss

New Member

JumpingPerson

Registered

dyst0pia

Member

JumpingPerson

Registered

Oklahoma Wolf

Senior Warranty Validity Sealed Stick Remover

JamesXP

Epic Fail Guy

AlabamaCajun

Member

wingman99

Member

Madnyss

New Member

Similar threads