Any downside to having a lot of extra power?

thinman400

Commendable
May 20, 2016
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Hey guys. I need to upgrade my power supply and I'm eyeballing a Seasonic Gold 650W. This is already plenty of juice for my system (over 200W headroom). Though, I've noticed I can get the 750W version of this psu for about $10 less.

Is there any big downside to having this much extra power?
 
Solution
Sorry, but "insulting to a question being asked for help and insight."?

Unless you were referring to the "Since you are apparently unable to read some charts let's spell it out for you:" that was actually addressing bjorn who doesn't even understand that at the level of a 650W vs a 750W PSU, the efficiency curves (i.e. efficiency at different level of load) dictate that PSU on the same platform performs very similarly to one another.

You can actually go to any reputable PSU reviewer, (Aris here on Toms or jonnnyguru, etc) and see that for yourself if the charts on how efficient the different EVGA B3s is still don't convince you.

His "Meaning it will convert a higher percent of the electricity it draws to waste heat at...
No. There's actually more benefits since it allows you to upgrade farther in the future. The PSU will only draw as much as it needs from the wall (as much as your system is pulling), so it's not going to be any more effective than a 500w PSU, but it gives you more breathing room for power requirements in the future.
 
There is downside, but not a huge one. The only issue is efficiency. A PSU is most efficient the closer to 50% utilization you are. Also you can get a crappy 1000watt for less than a quality 600watt. But I would rather have a quality 600watt.
A PSU is your foundation, don't get a bad one. If the 750 is as good as the Seasonic 650 (seems unlikely), then get the cheap one. Otherwise get the best quality one you are considering (I would again assume this to be the Seasonic 650)
 
No really. The higher wattage PSU will be less taxed and therefore generate less heat -> less fan noise; although technically they'd be a bit less efficient compare to the lower wattage PSU at that load.

@bjorn: doesn't he already stated that the 750W version of that Seasonic model is cheaper (sale/rebate/etc)?
 


This is not correct. Read the PSU primer on this site. A PSU is not very efficient when under a trivial load %. Meaning it will convert a higher percent of the electricity it draws to waste heat at 20% than at 50%. What matters most is the quality of the PSU and its efficiency rating but pretty close to that is getting the right size PSU for the task.
 


This is not correct. A PSU will only draw what it needs + what it is going to waste. If it is has 80% efficiency at 20% load (and very few are this good) then it will draw "wattage to use" x 1.25, where the .25 represents money (electricity) that will converted to waste heat inside your computer.
 


Id be tempted by the savings of the 750 up front vs the savings of the 650 using less electricity over time. But given how small the difference in use would be, I'd say get the cheap one only because unless you live in a place where the KW cost is extreme, then it would take years to "earn back" the savings from having closer to the right-sized PSU.
 
So if I'm understanding ya'll correctly, the closer to 50% utilization you are the better? I'm under the impression that often times systems might use significantly less power depending on the current task.

For example: Hypothetically, let's say my build requires 375W of power according to pcpartpicker. This would be exactly 50% of the 750W provided by the PSU. At first glance this would seem perfect, but if I am correct in my thinking, the system will almost always being using less than the indicated 375W.

Thoughts?
 
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Don't you start that BS efficiency arguments. 100W difference between the same model isn't going to suddenly send the PSU efficiency crashing through the floor.

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So if I'm understanding ya'll correctly, the closer to 50% utilization you are the better? I'm under the impression that often times systems might use significantly less power depending on the current task.

For example: Hypothetically, let's say my build requires 375W of power according to pcpartpicker. This would be exactly 50% of the 750W provided by the PSU. At first glance this would seem perfect, but if I am correct in my thinking, the system will almost always being using less than the indicated 375W.

Thoughts?

???
 
Since you are apparently unable to read some charts let's spell it out for you:

Even in an extreme example of 450W to 850W difference:

At ~200W the 450W EVGA B3 model operates at ~87% efficiency, its fan start ramping up at ~70W and at ~200W produces 24dbA.
At ~200W the 850W EVGA B3 model operates at ~86% efficiency, its fan start ramping up at ~170W and at ~200W it is almost inaudible >12dbA.

Is that clear enough yet?



Yes. When your 300W system idling it could just draw in the 100W vicinity. Even a 130W CPU + a 300W GPU can idling down to ~10W + ~50W range. Efficiency matter more when the system is under load because it's the math of 10% of 100W vs a few percent of 2-400W.
 

Here is the efficiency chart.
As you'll see it is more efficient at close to an ideal (50%) load, but it doesn't swing from 85% efficiency to 30%.
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How accurate PCpartspicker is, is another question. I think they're ok. Others on here think not so nice things.
The reason I'm ok with it, is I think it only has to show you what neighborhood you need to be in.
You're right in that if you need 375, than most of the time you'll be cruising at around 1/2 that.

 


Exactly, I'm already kind of bummed out about having to replace my current one that I've only had for a little over a year.
 


Gotcha thanks.
 

ftw, I goofed in the image post. Updated (see above).
 
As a novice builder, I frequently have similar type of questions. I can read multiple sites, but sometimes it also helps to have advice from more experienced individuals. FD2Raptor - your response is really disappointing to read as you are so insulting to a question being asked for help and insight.
 
Sorry, but "insulting to a question being asked for help and insight."?

Unless you were referring to the "Since you are apparently unable to read some charts let's spell it out for you:" that was actually addressing bjorn who doesn't even understand that at the level of a 650W vs a 750W PSU, the efficiency curves (i.e. efficiency at different level of load) dictate that PSU on the same platform performs very similarly to one another.

You can actually go to any reputable PSU reviewer, (Aris here on Toms or jonnnyguru, etc) and see that for yourself if the charts on how efficient the different EVGA B3s is still don't convince you.

His "Meaning it will convert a higher percent of the electricity it draws to waste heat at 20% than at 50%." is meaningless in this context. Here, even if I were to use his Wikipedia chart to do the math:

650W at 20% load (~130W) for 87% efficiency (149W drawn, ~19W waste):
750W at 20% load (~150W) for 87% efficiency (172W drawn, ~22W waste).

How big a difference does that 3 extra wasted watts make when a 400W system idling/web browsing at ~100-ish watts? Nothing.

650W at 50% load (~325W) for 90% efficiency (~361W drawn, ~36W waste)
750W at 50% load (~375W) for 90% efficiency (~416W drawn, ~41W waste)

So for your information, that's a total of 5 wasted watts compare to the 3 wasted watts at lower load between the two PSU.

It is when the system is under load that the actual amount of total wasted energy actually got significant enough, and even then for a 650W that is guaranteed to have lower efficiency past 50% of its rated capacity compares to a 750W from the same platform, the "extra wasted energy" is still far too low to actually matter, but the increase in either quality/capacity/quantity of its internal components to support the higher wattage rating will translate to less stress on the individual components (and therefore its temperatures) will matter (proven by the chart of fan noise/RPM which indicate the level of which engineers determine when components get hot enough to ramp up the fan to guarantee its safe operation, and so that they won't have to deal with a failed unit when its internals got/stayed too hot).

Even if you use some crazy number: 80% efficiency at 50W load? 62.5W drawn, 12.5W wasted. You just can't go low enough on low load efficiency to make a PSU waste so much more power at low load than it does at mid/heavy load (a good 80+ Gold will still maintain 70-75% efficiency at standby load, 2-15W load, 3-20W drawn).


So unless you think a PSU operates by the % rather than hard number of watts, volts, Celsius, etc; there just isn't evidence to support the go low on the wattage for max efficiency = best (it's just usually cheaper to go with enough wattage + headroom as needed/wanted and therefore why it's the general recommendation).
 
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