Radeon HD4850 and "LC Power" 550W question

**iban555** · 08-19-2009, 01:04 PM

I am going to acquire a latest HD4850, but before proceeding with it I did the investigate to observe if my power supply can handle it. Even after all the analysis I did, I am still not certain, so I want to ensure it up with the community. Here is the condition with
my existing PSU.

Brand: LC Power
Product code LC6550

Quoted power

Continuous power 550 W
Max. Current 12 V - Rail 1 16 A
Max. current 12 V - Rail 2 18 A

The following tests were done on the 12V rails :

Measured voltage 12V1 rail
4 A load (= 50 W @ 12 V) 12.15 V
8 A load (= 100 W @ 12 V) 12.03 V
12 A load (= 150 W @ 12 V) 11.93 V
16 A load (= 200 W @ 12 V) 11.83 V
20 A load (= 250 W @ 12 V) 11.75 V
24 A load (= 300 W @ 12 V) 0
28 A load (= 350 W @ 12 V) 0
32 A load (= 400 W @ 12 V) 0
36 A load (= 450 W @ 12 V) 0
40 A load (= 500 W @ 12 V) 0
Maximum load 12V1 (+3/4) within 5% margin : 21 A

Measured voltage 12V2 rail

4 A load (= 50 W @ 12 V) 12.09 V
8 A load (= 100 W @ 12 V) 11.94 V
12 A load (= 150 W @ 12 V) 11.82 V
16 A load (= 200 W @ 12 V) 11.71 V
20 A load (= 250 W @ 12 V) 0
Maximum load 12V2 within 5% margin 18 A

So on Rail V1 there are 21 A at utmost load, as well as as far as I know, HD4850 requires at least 18 A. Also, the PSU is listed at over 80% competence, but I had it for about two years now and if I am not mistaken, over time, the capacity drops due to wearing down of the part. Now, I have calculated total Watts’s handling and that should be very well, but I am distress about not providing additional amperage to the rail so that the card can run without having to go hungry for power.

If somebody could lean-to a bit more light if my concerns are sufficient? Particularly the two-rail thing is not completely clear to me, mainly does this means that if required the combined can be supplied to one of the rails, or the 21A max is all there is to the V1?

Thank you in advance.