Question Calculating '80 Plus' PSU power loss as Watts

[psucpugpu]

I'm trying to understand something about PSU efficiency using this copy/pasted definition of the 80 Plus certification...

"The 80 Plus certification tests the efficiency of a PSU at different loads. The loads are 20%, 50%, and 100% of the maximum power output. A PSU that is 80 Plus certified must have an efficiency of at least 80% at 20% load, 80% at 50% load, and 80% at 100% load."

So if I have a 470 Watt 80 Plus Bronze PSU that is pulling 235 W at the power point (i.e. operating at 50% load and therefore at 85% efficiency at the Bronze level) - is it saying that approximately 15% of that 235W is lost to heat and the actual load at the PSU output would be closer to 200W?

For context - I'm deconstructing a HP Z400 down to PSU, CPU, RAM, HDD and reduced power consumption is a side priority for that. I'm currently down to 165 W but I'm hoping to get down closer to 100 W and that would put me in the lowest efficiency bracket for the standard 470W power supply its currently fitted with so I need to consider that.

Thanks,

 

[sizzling]

The psu would still deliver 235w to the system but draw 276w from the wall. The difference between 235 and 276 is the power loss to inefficiency/heat.

 

[psucpugpu]

The psu would still deliver 235w to the system but draw 276w from the wall. The difference between 235 and 276 is the power loss to inefficiency/heat.

Ah - I've made a mistake in my numbers haven't I.

So in my example where the PSU is pulling 235W at the wall - that's not the load at the output of the PSU (i.e. not '50% load') that would be a load at the PSU output of closer to 200W (i.e. a drop from 235W of about 15%).

But the general idea stands yes? 85% efficiency equates to approximately 15% loss?

 

[sizzling]

Ah - I've made a mistake in my numbers haven't I.

So in my example where the PSU is pulling 235W at the wall - that's not the load at the output of the PSU (i.e. not '50% load') that would be a load at the PSU output of closer to 200W (i.e. a drop from 235W of about 15%).

But the general idea stands yes? 85% efficiency equates to approximately 15% loss?

Correct. When the system pulls 200w the draw at the wall would be 235w.

 

[Math Geek]

you got the basic idea right. take what's being pulled from the wall and compute the 80% or 85% or whatever. that's what the psu is using. keep in mind this is not 100% set in stone, but rather a guideline. it won't waste EXACTLY 10 or 15% or whatever. but it is a good approximation.

 

[geofelt]

A psu will draw only the power demanded of it, regardless of the max capability.
Efficiency is relevant mainly to the heat generated or the cost of electricity.

To reduce the power draw, you need to look at the components that are using power.
The usual ones will be the cpu and a gpu.