[SOLVED] What is the PSU efficiency rating?

[Jacob 51]

I used to believe that 85% efficiency rating on a 450 watt PSU meant that it can provide 382.5 Watts efficiently, but I was proven wrong, and I couldn't understand it.
I really want to understand how this works.
If a 450 watt PSU is rated Bronze with 85% rating, how much watts can it provide without having problems?

Does the rating actually matter?

If a PSU has a rating of 50%, will it be worse than the one with 80% efficiency rating?

 

[kanewolf]

I used to believe that 85% efficiency rating on a 450 watt PSU meant that it can provide 382.5 Watts efficiently, but I was proven wrong, and I couldn't understand it.
I really want to understand how this works.
If a 450 watt PSU is rated Bronze with 85% rating, how much watts can it provide without having problems?

Does the rating actually matter?

If a PSU has a rating of 50%, will it be worse than the one with 80% efficiency rating?

Maybe this article helps explain -- https://www.velocitymicro.com/blog/what-is-psu-efficiency-and-why-is-it-important/

 

[jay32267]

"If a 450 watt PSU is rated Bronze with 85% rating, how much watts can it provide without having problems? "

It SHOULD provide 450 watts....but many times, cheaper low quality PSUs output less than they say they do.

To find out what the maximum the PSU draws from the wall....divide the wattage by the efficiency.

So....450/85 = about 530 watts from the wall.

"If a PSU has a rating of 50%, will it be worse than the one with 80% efficiency rating? "
All things being equal....the 50% unit will give off more heat.

 

[Jacob 51]

"If a 450 watt PSU is rated Bronze with 85% rating, how much watts can it provide without having problems? "

It SHOULD provide 450 watts....but many times, cheaper low quality PSUs output less than they say they do.

To find out what the maximum the PSU draws from the wall....divide the wattage by the efficiency.

So....450/85 = about 530 watts from the wall.

"If a PSU has a rating of 50%, will it be worse than the one with 80% efficiency rating? "
All things being equal....the 50% unit will give off more heat.

If it draws 530 watts from the wall, can it provide 530 watts to the system?

 

[DSzymborski]

I used to believe that 85% efficiency rating on a 450 watt PSU meant that it can provide 382.5 Watts efficiently, but I was proven wrong, and I couldn't understand it.
I really want to understand how this works.
If a 450 watt PSU is rated Bronze with 85% rating, how much watts can it provide without having problems?

Does the rating actually matter?

If a PSU has a rating of 50%, will it be worse than the one with 80% efficiency rating?

It's just that you're multiplying when you should be dividing. 85% efficiency doesn't mean that when a PSU wants 450 watts, it can only get 382.5 watts, it means that when a PSU wants 450 watts, it draws 530 watts from the wall.

As opposed to "without having problems" the efficiency rating simply means efficiency; it's not an indication of how "good" the PSU is at other stuff. There's a correlation -- it's easier to develop a garbage PSU that fails 80 Plus than one that legitimately gets a Platinum 80 Plus rating -- but it's still an efficiency, not a quality rating.

 

[jay32267]

If it draws 530 watts from the wall, can it provide 530 watts to the system?

No....that's where the 85% comes in,

530 watts times 85% is 450 watts

15% goes as heat

 

[Jacob 51]

No....that's where the 85% comes in,

530 watts times 85% is 450 watts

15% goes as heat

Oh I see... So in a 50% efficiency PSU the other50% will go as heat, causing more heat to generate

 

[Jacob 51]

So....450/85 = about 530 watts from the wall.

Wait a minute, 450/85 will be 5.29, and not 530

 

[kanewolf]

Wait a minute, 450/85 will be 5.29, and not 530

You are going to quibble over tenths of a watt ????

 

[DRagor]

Does the rating actually matter?

If a PSU has a rating of 50%, will it be worse than the one with 80% efficiency rating?

The main difference would be your electricity bills would be higher with 50% rating unit then with 85% rating unit.

 

[jay32267]

Wait a minute, 450/85 will be 5.29, and not 530

I said "about".
Even with the best PSUs...I doubt they are accurate to "the watt".

 

[Jacob 51]

I said "about".
Even with the best PSUs...I doubt they are accurate to "the watt".

You are going to quibble over tenths of a watt ????

I didn't get it, I didn't mean to criticize

 

[jay32267]

I didn't get it, I didn't mean to criticize

...but you get it now right?

To get the max output at the wall.....divide the labeled output (provided it is correct) by the efficiency.

That's all it is.

 

[mikewinddale]

Here's a Wikipedia article about the efficiency ratings.

The efficiency of a computer power supply is its output power divided by its input power; the remaining input power is converted into heat. For instance, a 600-watt power supply with 60% efficiency running at full load would draw 1000 W from the mains and would therefore waste 400 W as heat. On the other hand, a 600-watt power supply with 80% efficiency running at full load would draw 750 W from the mains and would therefore waste only 150 W as heat.

As others have noted, the power supply can/should always be able to supply its rated power. But it draws even more power from the wall than that.

For easy math, let's assume a 100W power supply. A 100% efficient PSU would draw 100W from the wall and provide 100W to the system. A 50% efficient PSU would still provide 100W to the system, but it would draw 100/0.5 = 200W from the wall.

The 80 Plus certification will certify different levels of efficiency when the PSU is providing different percentages of its maximum output. For example, according to that Wikipedia link, an 80 Plus Bronze PSU will be 82% efficient when outputting 20% of its maximum load, 85% efficient when outputting 50% of its maximum load, and 82% efficiency when outputting 100% of its maximum load. The 80 Plus Bronze standard specifies no level of efficiency at 10% load. Meanwhile, an 80 Plus Titanium PSU will be 90% efficient at 10% load, 92% efficient at 20% load, 94% efficient at 50% load, and 92% efficient at 100% load.

There are two benefits of higher efficiency: less power draw (so a lower energy bill), and less waste heat (so quieter fans).

I suppose a more efficient PSU might live longer too, since it has less heat. On the other hand, if it takes advantage of the reduced heat by running its fans slower and quieter, then it might end up having just as much heat, so maybe it won't live longer. I'm not sure.

Personally, I use the 80 Plus certification as an extra check for overall PSU quality. I figure, if the PSU is high-enough quality to be independently certified as highly efficient, then it's probably very high quality in other ways too. That's probably not a 100% certain way of testing PSU quality, but I figure, it's one more thing.