Sign in with
Sign up | Sign in
Your question

Radeon HD4850 and "LC Power" 550W question

Last response: in Graphics & Displays
August 17, 2009 9:39:09 AM

Good day everyone.

I am going to get a new HD4850, but before proceeding with it I did the research to see if my power supply can handle it.
Even after all the readings I did, I am still not confident, so I want to check it up with the community. Here is the situation with
my current 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 maximum load, and as far as I know, HD4850 requires at least 18 A. Also, the PSU is listed at
over 80% efficiency, 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 component. Now, I have calculated total Watts usage and that should be fine, but I am concern about
not providing an extra amperage to the rail so that the card can run without having to starve for power.

If someone could shed a bit more light if my concerns are adequate? Especially the two-rail thing is not completely clear to me,
basically does this means that if needed 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.
a b U Graphics card
August 17, 2009 12:39:28 PM

Is there a combined 12v maximum wattage or amperage?
That's what counts.

Any way you should be fine with that amperage.
August 17, 2009 12:50:47 PM

Yes, the combined wattage listed on the PSU is 380W.
Related resources
a b U Graphics card
August 17, 2009 1:17:35 PM

That translates to 32 amps.
August 17, 2009 1:40:49 PM

Sounds good enough. Mind if I ask also this - the techie guy at the store implied that I am better off ordering a HD4770 since
the price difference is larger and the difference in performance is not as big. Is that plausible ? I saw a few benchmarks here
and there, and seems 4770 is not as persistent in general. On some bench it beats its NVidia counterparts and even the 4850,
and on some is on-par with the 4830.

I knew that would happen, always the techie guy at the store messes up with my pre-made plans! :) 
August 17, 2009 1:47:17 PM

Hi. I'm currently running the Powercolor HD4850 1GB PCS+ with a thermaltake tr2 430W PSU.

I tried a generic 450W PSU (Minimum recommended with the card) and it barely managed to run with 1HD and DVD-RW connected!
A generic 350W could not even start the fan on the GPU!

The Thermaltake is managing the HD4850, with 6HD's and DVD-RW without breaking a sweat! And i still have 5 Molex connectors to spare.

Hope this helps u out.
a b U Graphics card
August 19, 2009 11:48:24 AM

Welcome to the fourms!

Please read this review about your power supply:

The main problem with this power supply is that it can’t deliver its labeled power. It is, in fact, a 350 W power supply.
August 19, 2009 2:01:13 PM

Thank you all for the replies.

After looking around, I decided to upgrade the PSU and change the model of the card. So, now I am going for a Gigabyte HD4890 1GB DDR5.

The PSU I bought is a Chieftec APS-650C.

The rest of the upgrades will come in time, based on the budget I guess ;)