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Downside to too much power?

R

Ronin13

Senior member
I'm planning a new rather basic build: 2 case fans, 1 optical drive, 1 or 2 SSDs, 2 DIMMs, maybe a soundcard, 1 CPU and 1 GPU.

I might go as low as a i3 4170 (54W) with a GTX 750Ti (60W) or as high as a i5 4690 (84W) with a GTX 960 (120W).

As far as I understand, PSU aren't at their most efficient with a low power draw, but on the other hand they also don't tend to get loud before they're significantly pushed.

I'm guessing a good 450 W PSU could run the above, but since I would like some overhead and would like to keep the PSU quiet, I think my minimum should be 550 W.

And since a 650 W is only about $10 more (for the models I'm looking at), I'm starting to lean in that direction.

Aside from the slightly lower efficiency at the power levels I need (and the difference here must be negligible between a 550 and a 650 W?), are there any concerns with having 'too much' power? Like reduced lifespan if the PSU doesn't get a good workout now and again?
 
Other things to think about is whether the ripple and voltage regulation will be as good when the psu is running at very low power levels, its like the cross loading tests in reviews.
 
Ronin13 said:
I might go as low as a i3 4170 (54W) with a GTX 750Ti (60W) or as high as a i5 4690 (84W) with a GTX 960 (120W).

I'm guessing a good 450 W PSU could run the above, but since I would like some overhead and would like to keep the PSU quiet, I think my minimum should be 550 W.

And since a 650 W is only about $10 more (for the models I'm looking at), I'm starting to lean in that direction.

Aside from the slightly lower efficiency at the power levels I need (and the difference here must be negligible between a 550 and a 650 W?), are there any concerns with having 'too much' power? Like reduced lifespan if the PSU doesn't get a good workout now and again?
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I don't follow your logic.

I would think a 450 watt PSU would provide plenty of overhead. I'd guess your load would rarely exceed 200 watts and would usually be below 150 unless you are gaming non-stop 24/7. A 450 watt PSU would likely be right in the highest and flattest part of it's efficiency curve in that situation.

If a 850 watt PSU was only 10 dollars more, would you start to lean in that direction and if not, why not? No doubt, plenty of people would and do.

No, the "good workout" thing is pointless.

The "concerns" about "too much power" relate to the initial cost of an unnecessarily powerful PSU and the extent to which any given PSU does NOT have a flat efficiency curve---a straight line, not a curve, ignoring PSU quality issues.

You should be able to look at the efficiency curve for any tested PSU. For a good unit, it should be near flat for most wattage levels, with a trailing off of a few percentage points at each end. The drop-off is minimal for decent units when you get to above say a 50 watt level.

The efficiency drop-off has a slight effect on your power bill, when compared to some other more efficient PSU, irrespective of its wattage rating.

It doesn't amount to much. I did the calculation for my own hardware. At 14 cents per KWH (near the national average), 14 hours per day operation, and similar hardware to yours, a 5% drop in efficiency would amount to less than $1 per month in additional power usage.

Of course, 650 will always be a larger number than 450 and I suppose that counts for something.
 
if you stay between 50% and 75% of the PSU load, you will get all the benefits and none of the downsides.
 
Thanks for your replies.

ignatz, I'm not looking for a larger PSU simply because of its higher number, as you seem to be implying. What I'm interested in, is enough overhead to be sure to keep the noise down (as long as there are no downsides to a slightly beefier PSU than needed).

You're saying that a 450 W would adequatedly supply that overhead, that's good to know. Are you also saying that, initial cost aside, there are no downsides to going with a 550 or 650 W PSU, but that you would advice against it?
 
Ronin13 said:
T

You're saying that a 450 W would adequatedly supply that overhead, that's good to know. Are you also saying that, initial cost aside, there are no downsides to going with a 550 or 650 W PSU, but that you would advice against it?
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I personally would not go with above 450.

Why:

1: Given your own projections regarding components, including the most power-hungry choices, you would not draw anywhere near enough power to strain a decent 450.

2: The extra money I might spend could be put to better use.

3: If I bought a 550 or 650, I would typically be operating at a lower point on the efficiency curve than I would with a 450, given the anticipated power you will need. How much penalty you would pay for being at a lower point on the curve would vary unit by unit and would require further research. As I said, it isn't much--typically maybe 50 cents a month given average power rates. It could even be zero in the case of certain highly efficient PSUs that are just as efficient at a 15 percent load as they are at a 40 percent load. You'd have to examine that on a case by case basis.

So there is an initial cost, and may be a monthly cost as well--to be determined by what you actually buy. All of that may mean nothing at all if you get some sort of personal reward by having a 650 watt PSU rather than a 450 watt PSU that in your mind compensates for the difference. This is where terms like "future-proofing" and "headroom" are trotted out to explain the personal reward.

Noise levels would certainly be a factor to me, but you certainly can't assume that 650 watt PSU A would necessarily be quieter than 450 watt PSU B when both are under identical load. Maybe and maybe not. Varying from model to model and case by case.

I'm assuming that the 2 hypothetical PSUs are identical in all other respects--build quality, ripple, warranty, etc.
 
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Thank you.

Discussing my power requirements and specific PSU recommendations over here: http://forums.anandtech.com/showthread.php?t=2436125 has led me to believe that the 80+ Gold rated units I was looking at are unnecessary, and I'm now looking at the 80+ Copper rated Seasonic S12II 520 W, as it seems to have just as good (or better) efficiency at low power levels.

Of course, if there's another unit (in the same price ballpark) you'd recommend, please do.
 
there is just one thing to be added though; in real life, the higher wattage you go, the better quality components you get. better transistors, better cooling.

i'm not saying you should use a 1000w PSU on a 300w system (because efficiency, and also, actual cost), but a 1000w psu that runs at 300w will last longer than a 600w psu that also runs at 300w. both wattages are totally within the "i am not even bothered" range, but the more expensive PSU will generally have higher quality components in it.

you can almost always avoid guessing if you look at jonnyguru.com as he posts some very indepth reviews and you will know exactly what you are buying.
 
Ronin13 said:
Thank you.

Discussing my power requirements and specific PSU recommendations over here: http://forums.anandtech.com/showthread.php?t=2436125 has led me to believe that the 80+ Gold rated units I was looking at are unnecessary, and I'm now looking at the 80+ Copper rated Seasonic S12II 520 W, as it seems to have just as good (or better) efficiency at low power levels.

Of course, if there's another unit (in the same price ballpark) you'd recommend, please do.
Click to expand...

Antec Neo Eco 520C is a rebadged S12II (pretty sure). I use one, no issues.
 
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