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TechnoZamb19

Does efficiency reall matter anyway, and do we really need powerful PSUs?

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Posted · Original PosterOP

My computer eats about 350W on full load (RX 580, Ryzen 5 1600). Many PSU calculators suggest me bronze 650W - 700W PSUs. This is because in order to reach maximum efficiency we need to use about 50% of what our PSU can output. But... does it really matter?

 

A 80 Plus Bronze PSU, which is the most common type, will give:

- an 82% efficiency under 25% load;

- an 85% efficiency under 50% load;

- an 82% efficiency under 75-100% load.

We can see that our efficiency changes very little, only about 3%, on all possible loads, from 25% to 100%.

Now, taking my pc as a point of reference, let's equip it with a 700W PSU, which will result in a 50% load. Our efficiency will be about 85%, which means our PSU would draw 350W / 85 * 100 = 411W from the wall.

Let's give my pc a 450W PSU, which will result in a 75% load (slightly more than that). Our efficiency will be about 82%, which means our PSU would draw 350W / 82 * 100 = 426W from the wall.

 

That's a 15W difference. Where I live, we pay 0.24€ per KiloWatt hour. If I used my pc 5 hours a day, every day UNDER FULL LOAD (which is very unlikely) I would pay 15W * 5 * 365 / 1000 * 0.24€ = 6.57€ more per year, or 7.75$ for you American folks.

 

Conclusion: is it really worth spending 30-40€ more for a more powerful PSU, that can always stay at maximum efficiency?

I'd like to know your opinions.

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Noise and longevity. While I could run this system on a cheap 450w bronze unit, I'd rather use my platinum 750w unit instead.

 

*Originally was going to build with the 650w version, but the 750w was on sale lol


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11 minutes ago, Crunchy Dragon said:

I personally plan on getting 80+ Platinum or Titanium PSUs for when I start mining since they'll be running 24/7 at load.

This.  It depends what you are using the computer for.  If it's on 24/7 at full load, like Mining, Folding etc. then a higher quality PSU is a good idea.  Higher quality components are usually inside higher efficiency PSUs.

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8 minutes ago, TechnoZamb19 said:

My computer eats about 350W on full load (RX 580, Ryzen 5 1600). Many PSU calculators suggest me bronze 650W - 700W PSUs. This is because in order to reach maximum efficiency we need to use about 50% of what our PSU can output. But... does it really matter?

 

A 80 Plus Bronze PSU, which is the most common type, will give:

- an 82% efficiency under 25% load;

- an 85% efficiency under 50% load;

- an 82% efficiency under 75-100% load.

We can see that our efficiency changes very little, only about 3%, on all possible loads, from 25% to 100%.

Now, taking my pc as a point of reference, let's equip it with a 700W PSU, which will result in a 50% load. Our efficiency will be about 85%, which means our PSU would draw 350W / 85 * 100 = 411W from the wall.

Let's give my pc a 450W PSU, which will result in a 75% load (slightly more than that). Our efficiency will be about 82%, which means our PSU would draw 350W / 82 * 100 = 426W from the wall.

 

That's a 15W difference. Where I live, we pay 0.24€ per KiloWatt hour. If I used my pc 5 hours a day, every day UNDER FULL LOAD (which is very unlikely) I would pay 15W * 5 * 365 / 1000 * 0.24€ = 6.57€ more per year, or 7.75$ for you American folks.

 

Conclusion: is it really worth spending 30-40€ more for a more powerful PSU, that can always stay at maximum efficiency?

I'd like to know your opinions.

 

One thing you didn't consider is that most 700W PSU is at least 80+ Gold if they are good. Which if we do 350W / 90 * 100 = 389W. 

Then the difference between 426W and 389W is 37W then: 

37W * 5 * 365 / 1000 * 0.24 = 16.88€ which is 22.75$ now that's a bit more saving but still, not much another thing is that the better PSUs (Like 700W 80+ Gold) are generally better quality than 350W 80+ Bronze ones. If you look enough you can even find a 700W 80+ Platinum (They isn't too much of a price difference).

 

Its more of a dose that little bit of money matter, I would recommend getting a bit of a better PSU in case you ever decide to add something that will draw more power without having to buy a new PSU and get a better efficiency which will matter more. 

IMO there is no reason to get an 80+ Bronze 700W PSU or getting a higher wattage PSU, in general, to run a 50% load but instead to slightly future proof and get higher quality PSU.

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even $7.75 is basically $40 over the 5 year minimum warranty of a quality high efficiency unit with most having a 7 to 10 year warranty, you have to look at the LONG TERM a PSU can go from one build to the next as you upgrade your computer so having a higher efficiency unit saves more money in the long term

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10 minutes ago, TechnoZamb19 said:

My computer eats about 350W on full load (RX 580, Ryzen 5 1600). Many PSU calculators suggest me bronze 650W - 700W PSUs. This is because in order to reach maximum efficiency we need to use about 50% of what our PSU can output. But... does it really matter?

[..]

That's a 15W difference. Where I live, we pay 0.24€ per KiloWatt hour. If I used my pc 5 hours a day, every day UNDER FULL LOAD (which is very unlikely) I would pay 15W * 5 * 365 / 1000 * 0.24€ = 6.57€ more per year, or 7.75$ for you American folks.

 

Conclusion: is it really worth spending 30-40€ more for a more powerful PSU, that can always stay at maximum efficiency?

I'd like to know your opinions.

I keep my pc running 24/7 , it's easier on the components (mechanical hard drives and motherboard and even fans).

PC idles at 100-120 watts due to having 4 mechanical hard drives and an old FX-8320 that's does't lower it's power much when idle

When gaming, it's probably close to 300 watts.

 

Bronze rated power supplies are less efficient when idle, at 10% or so of their output the efficiency often drops to 80% or even less.

In my case with a bronze efficiency If you keep the system running 24/7 using 100w, that's 25w of wasted

I have a Seasonic X-650 Gold Efficiency power supply which is 89% efficient at ~ 10ww, so it's only 12w of wasted electricity. In addition, the fan is off until i hit around 160w so i get silence, and then over 160w the fan barely spins until around 250w.

 

So for 24/7 use, going with this more expensive gold efficiency psu was a savings of around 13w per hour or 312 watts (0.3 kWh per day) or 9.672 kWh ... let's just round it to 10kWh for easy math or 120 kWh in a year.

I'm paying around 0.57 RON (0.12 euro) per kWh with taxes included, so in a year I'm saving 0.12 x 120 =  14.4 euro

When I bought this power supply, the price difference between a quality bronze efficiency power supply and this one was somewhere around 40-50 euro, so I'm basically recovering the extra money spent on this power supply in around 3-4 years.

I'm sure this power supply is quality enough that it will last me more than 5-6 years, pretty sure even 10, and i have the added benefits of passive cooling at idle (less noise) and less heat produced in the house, and also "purer" power to components since it's a higher end power supply.

 

So basically it's a bigger upfront investment which you technically recover in a few years by power savings, depending on how you use your computer.

In my case, i consider the extra 30-50 euro a year in electricity by keeping my pc running 24/7 worth it so it makes sense to aim for higher efficiency at idle (for example 8-14 hours while i sleep or i'm away from pc) , since the risk of components dying is reduced by a big enough percentage in my mind to be worth it.

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38 minutes ago, M.Yurizaki said:

You also have to consider how much extra heat the PSU is dumping. From your 350W calculation, you're dumping 61 watts of heat into the system. So it could creep beyond just how much power the PC uses.

Less heat means less noise from cooling too.

I generally go for more efficient PSUs but I won't replace old inefficient ones.  My main HTPC has a Corsair TX750, the thing isn't eve Bronze, it's not what I'd buy NEW now but I'll use it till it fails and replace it with something more efficent.

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There are many reasons to buy a high quality PSU that is rated to deliver more than what you actually need...not doing so IMHO is dumb.


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Posted · Original PosterOP
5 hours ago, M.Yurizaki said:

You also have to consider how much extra heat the PSU is dumping. From your 350W calculation, you're dumping 61 watts of heat into the system. So it could creep beyond just how much power the PC uses.

How did you get those "61 watts" of heat?

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Posted · Original PosterOP
1 minute ago, M.Yurizaki said:

If 350 watts are being used out of 411 watts being pulled, where do you think the remaining 61 watts goes to?

Ok then the point of your first comment is? Why should it "creep beyond how much power the PC uses"?

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1 minute ago, TechnoZamb19 said:

Ok then the point of your first comment is? Why should it "creep beyond how much power the PC uses"?

Because that heat can generate secondary effects like making your room toasty, and therefore you need to turn on the AC or have some other method of cooling the room down. Also as other people mentioned, having higher heat loads on the PSU will cause the components to fail faster.

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6 minutes ago, TechnoZamb19 said:

Ok then the point of your first comment is? Why should it "creep beyond how much power the PC uses"?

The other components becoming less efficient as they have to deal with more heat and fans need to work harder to keep things cool (and then fans in your room also need to work a bit harder, but heat would need to work a bit less). Although it's an irrelevant amount (hence 'creep').

 

In regards to your original question -- most PSU calculators don't give their estimates based on efficiency curves. They do it because they over-provision. In a typical desktop efficiency really isn't a big concern -- the reason you should pay more for a PSU is for a higher quality PSU (which often ends up meaning also paying for a higher wattage and higher efficiency PSU in the process).


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Posted · Original PosterOP
1 minute ago, M.Yurizaki said:

Because that heat can generate secondary effects like making your room toasty, and therefore you need to turn on the AC or have some other method of cooling the room down. Also as other people mentioned, having higher heat loads on the PSU will cause the components to fail faster.

I see. Also more heat will make your psu fan spin faster, which of course results in more power needed.

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Fans use very little power, typically less than 2 watts. You can look on their labels, you will see something like 12v 0.15A .. that's 12x0.15 = 1.8 watts at max rpm.

 

Only server fans use lots of power and are noisy.

 

later edit:  special fans for high static pressure, designed to push a lot of air through fins, for example fans for watercooling heatsink may also use a bit more than 2 watts, but generally a relatively low amount, let's say less than 5-10w.

 

 

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Let's disregard savings and look at this from the perspective of an enthusiast spending 1k+ on their build.

 

A higher wattage psu will allow for fanless mode, will generally be higher quality and come with nicer cables (probably modular) and if they keep the psu for its full 5-10 year lifespan the savings will stack up

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