NoviceTechie

Greetings,

I came to post today to seek some clarification on some PSU terms. I'm not an engineer major, but I do occasionally work with computer hardware.

My questions are regarding on AMPs (A).

I'm using a Thermaltake Toughpower 850 (http://www.thermaltakeusa.com/Produc...4&ID=1503#Tab1).
It has numerous A's running on 4 different +12v rails. (unless I'm misreading)

I've read the sticky in regards to PSU choice. I've even read the Johnnyguru post (http://www.jonnyguru.com/forums/showthread.php?t=3990). I also found this post in these forums (Power for GPU - 20 Amps per rail OK?)

Thermaltake's site advertises 62 A of combined power on +12v.

12v1 - 18A
12v2 - 30A
12v3 - 30A
12v4 - 18A

1.
The listed cumulative maximums, which should equate to 96A, is only 62. Is this due to the 30% degradation point made in the forum stickey?

The only connections I'm using are

1. 24 pin (12v3 - 30A(max)),
2. 4 pin (12v1 - 18A(max)),
3. Peripheral (4 fans + dvdrw, - 18A(max))
4. Sata x 1 (12v4 - 18A(max)).

*My graphics card is a 9500 gt, it doesn't require a pci-e power plug.

2.
Since only 12v1+12v3+12v4 are in use - do I only add up the max A on each rail - so 66 * .3.. At max load, would I only be using around 46.2 amps combined?

3.
Next, I don't mean to spark a debate between single rail and multirail, but for multirail PSU's - is it really as simple as adding the values for each rail, and degrading that value by 30% to arrive at my cumulative max A?

In other words, for any (A) needed, is the load split between multiple rails? I.E. if the PC requires 50 A, does it take the Max load from +12v3, then request more from +12v1 and +12v4 ? (I have a feeling I should know this one, but I'm not an expert at electronics.)


4.
Is there any credence to the point that if a component on one rail is only using 40% of the rail's Max A, 60% is trapped on that rail and can't be allocated elsewhere?

5.
The next part of my question might belong to the video card section, but its about the PSU too..in retrospect it extends from question #3. I ask because I'd like to upgrade to a Nvidia gtx 260 vid card. @ minimum the gtx 260 states "# PSU: For a single GeForce GTX 280 GPU you need a 550W PSU with 40A on the 12V rail. " The 260 also requires 2 (6) pin pci-e plugs. Given that the Thermaltake's 2 (6) pin pci plugs utilize +12v2 and +12v3 (both of which support 30 A max), then the GTX 280 would work just fine in my setup?


I apologize for the wall of text and if question #5 doesn't belong in this particular forum.

Thank you in advance for any help.
P.S. Apologies if I don't respond immediately (posting b4 I leave for the morning).

Phædrus2401

1.) Kind of. The PSU can deliver only 62A of current at +12V, total, and it can then deliver that power on any of the four rails at up to the maximum listed.

2.) What?

3.) No, it isn't that simple. The 30% thing is just a quick-and-easy approximation. With a split-rail configuration... If you have two rails at twenty amps each, and on one rail you're pulling 20A and on the other you're pulling 5A. Let's say the rail delivering 20A needs to be delivering 25A. Well, the other rail has 15A available for use, but the more-heavily loaded rail can't use it because it's on the wrong rail.

Among the tech team there is no debate between single rail and multirail. We recommend single rail units whenever possible, though we also acknowledge quality split-rail units from the Thermaltake Toughpower line and CoolerMaster Real Power Pro line.

4.) Exactly.

5.) The GTX260 will be drawing power from the motherboard and from the PCIe connectors. Since +12V3 (with the 24-pin connector) has 30A available, and the PCIe connectors are presumably on +12V2 which has 30A available, you will ample power for a GTX260. Don't try to power too much more off that though.

NoviceTechie

Thank you for the reply. I hope you don't mind, but I do have some follow-up questions.

I admit, I should've read the forums before considering a multirail psu over a single rail.

I suppose my confusion is over the allocated (A) on each rail. In a hypothetical situation, suppose a single device on one rail is asking for more (A) than the rail can provide. Will the device just shutdown (or perhaps the PSU will), or can it reallocate more (A) through another rail that is connected to the motherboard (i.e., if +12v1 is about to be overloaded, can it reroute more (A) through the motherboard, directly into the device asking for more power)?

When a gtx 260 lists that it need a 550 w psu + 46 (A), would I be correct in assuming that the entire system should be able to support the exaggerated overhead of 46 (A), not not that the card itself is drawing 46 (A)? So any PSU that states that it has a combined output of 60 or more (A) should be able to support the entire system?

Phædrus2401

If a more power is drawn from a rail than it can deliver then one of two things will happen. A.) The OCP (Over Current Protection) will kick in and shut off the power supply, or B.) If there is no OCP then it will just attempt to deliver that power until either the PSU malfunctions and dies, or the device can't get enough power and crashes. Extra power cannot be routed through the motherboard.

I think I understand what you're saying... The GTX260 should have a 550W PSU with *at least* 46A on the +12V rail. The system should be able to run on 46A. The GTX260 draws up to about 30A under full load (there's no reliable data on this, but based on the wattage it pulls that's a reasonable guess), and so the rest of the system should manage on the remaining 16A. We actually recommend a 650W; the Corsair TX650W is ideal. Yours will work, however.