Minimum PSU for a Quad Core and a G80 or R600....

Question

What's the minimum PSU wattage you'd recommend for a system?  I'll tell ya what I currently have and what I'm planning on getting.  Here's what I have: A64 X2 [email protected], 2GB 4x512MB of PC3200 Corsair ValueRAM, MSI K8N Neo4 Platinum mobo, GF 7800 GTX 512, Sound Blaster X-Fi XtremeGamer Fatal1ty sound card, 1 Lite-On DVD-ROM, 1 Lite-On DVD burner, 1 WD IDE 7200RPM HD, 1 Seagate SATA 7200 RPM, 1 Floppy, 1 Enermax 535 watt PSU, 5 80mm case fans.
Now, here's what I want to build:  Core 2 Quad Q6600, 2GB 2x1GB of DDR 667MHz Corsair XMS RAM, G80 or R600 (whichever comes out first), MSI P965 mobo, Sound Blaster X-Fi XtremeGamer Fatal1ty sound card, 1 Lite-On DVD burner, 1 Floppy, 1 WD IDE 7200 RPM HD, 1 SATA Seagate 7200 RPM HD, 5 80mm case fans and I want to use my 535 Watt Enermax PSU if I can.  According to this PSU calculator, I'll only need a 408 watt PSU if I buy the G80 (GF 8800 GTX) http://extreme.outervision.com/psucalculatorlite.jsp
My Enermax 535 PSU says on the sticker that is has two 12v rails and they each have 18a.  The total 12v amperage is 34a.  Is that enough or am I cutting it too close? 
Now, do you guys agree with that assessment or should I get a new PSU too?  The problem is, I really don't have enough money to buy a new PSU, otherwise, I'd get one in a heartbeat...the PC Power and Cooling Quad 750 watt PSU to be precise for $199 at Newegg, but I don't have the extra $200 or else I would.  I'd rather have allot of overhead but I just can't afford it now.  Another alternative is getting the E6600 Dual Core, in which case I'll have enough money to buy the PCP Quad 750.  Whatever happens I'm waiting until April 22nd where Intel drops their prices on their CPU's so the currently expensive Q6600 will drop down to a more manageable $530.   

Answer 1

Quote from: Jack the Newbie on 29-March-07, 07:35:00
I just read a thread in which someone had some problems with his system.  He was using a 550W DUAL-RAIL PSU (18A and 16A).  The combined maximum power for both +12V-rails was 250W (250W/12V=20.8A).  That means if the 18A-rail is at its maximum only 2.8A are left for the 2nd rail.  If you think about it, it sounds like a yoke, but it seems to be true:
It's not a joke. All these multi rail 12V PSU's only have a single rail control circuit inside, wich is split into multiple rails each with 20A or less current limit. I've only seen 1 multi 12V rail PSU in all these years wich truly has 2 control circuits inside.
The reason for this is plain safety. There is a safety standard IED 60950 wich limits wiring to a 240VA limit (12V * 20A = 240VA) and thats the only reason they make these multi rail psu's.
I've seen single rail PSU's with more then 50A on the 12V rail, that's enough to weld with ! But still they use the same thickness of wires as other PSU's otherwise people would complain about the wires not beeing flexible etc.
Such a single rail psu can deliver 49A trough 1 wire without tripping any safeties - melt the wire and cause fire because standard 1.5mm² cables used for PSU's are only rated about 20A - A multi rail PSU, even when its a just a single rail internally with splits will limit every outgoing connection to 20A or less thus protecting the wires.
The only reason you could call multirail psu's bad is because of bad specification by the manufactureres, who don't always supply the right numbers like combined power. But they are safer.
You should look at the psu above as a single rail 20.8A PSU with a 16A current protection on the CPU power connector and a 18A current protection on the other wires. When you look at it like that its not so bad is it ?