AMD recommends 400w but might run fine on 250w, That card doesn't draw more than 31 watts maximum
Roodo, I've seen that power consumption figure before, and it never seems to come supplied with documentation. I think this test from Anandtech.com is more useful. So the headings of the test results may be a bit confusing, but if you take the time to read the entire evaluation, it's pretty clear that the video card can pull about 200 Watts. The test also notes that the evaluation rig pushed the limits of the 1200 Watt PSU. So, clearly, a 250 Watt PSU isn't sufficient for this system.
Sorry but those are "Total System Power Consumption" figures. I.e. with the CPU, disks and everything else that may be in the test system. The HD6450 graphics card alone will never draw 200w. They don't even require a separate PCIe lead. The limit for a x16 PCIe card without separate PCIe leads is 75 watts (Source). The "pushed the limits of a 1200 watt PSU" at idle is because such a massive PSU would be struggling to run at such low levels (bearing in mind overall system power draw here is only 144w) and would be well outside the output range where it operates at best efficiency. For this reason (they speculate) the HD6670, 6570 and 6450 all showed the same system power consumption at idle, despite the HD6670 being a significantly more powerful card than the HD6450.
That's wrong. Again, I suggest you actually read the evaluation and not the headings on the graphics. Surely, you aren't so ignorant and ill-informed as to suggest that a large capacity PSU can't sustain the requirements of a low power system. are you? Certainly, you aren't trying to tell me that a high power PSU will effectively overload because there isn't enough load on it to function within design standards? Oh, but wait... you are. You need to do some serious homework on power supplies.
Here another point you seem to overlook: given that it's desirable for hardware to be power efficient and run on fairly low level and crappy under powered systems, why would AMD overstate the power requirements for the card? Dang! I don't think that's a strategy designed to boost sales! Anyway, I'm always open to being proven wrong, so I'm waiting.
I'll just restate that those are figures are for total system power consumption and not graphics card power consumption. If you think that a graphics card can somehow pull 200+ watts through the PCIe port alone, then you are wrong. The PCIe specification limits cards power draw through the port to 75 watts as already stated. The HD6450 uses a lot less than this however (claimed 18-27 watts depending on version). In order to pull 200 watts, an 8 pin PCIe connection to the card is required. The Radeon HD 6450 does not need an 8 pin PCIe connector, or a 6 pin PCIe connector. It's powered directly by the port.
And no I am not suggesting that a 1200 watt power supply can't supply the power required for a low end system or that it will in any way "overload". I am suggesting that it is outside of it's range where it is operating at it's best level of efficiency. Simply put, a power supply should be sized appropriately for the application. Testing power consumption for a low end single graphics card system with a 1200 watt PSU is silly and smacks of poor test design or laziness on the part of the testers. Some homework for you - http://www.anandtech.com/show/2624/3 Note what happens to efficiency when the 900w PSU is loaded to only 100w. Low efficiency means that more energy is being wasted as heat.
Lastly I could only speculate on why AMD makes the choices it does. Making blanket recommendations for easy consumption by the general public involves lots of assumptions and a need to "cover their ass" by being on the safe side. Assumptions about the rest of the system, assumptions about the age and quality of the PSU customers are likely to be using. Also a reasonable rule of thumb is to go for a PSU about twice the estimated power consumption (source). So if you have a system that is estimated to use 150 watts peak, it would be reasonable to go for a 300 watt PSU. This gives both headroom for expansion and allows for the PSU ageing and should get it in the 'sweet spot' of the efficiency curve most of the time.
Edited by jonuk76, 03 January 2014 - 09:35 PM.