Question Noob question about PSU wattage draw

Jul 10, 2020
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This is probably a dumb question to ask but I wanted to make sure. I am finishing up a basic home server for myself that will be used for mostly data storage on my home network and for streaming movies. The calculated wattage I would need with my setup is 285 watts of power for a PSU. I have an older 600 watt PSU that I'm going to use but my question is will a lower wattage PSU be better for efficiency, (less power draw overall). Or would it not really matter if the demand isn't there because the system wouldn't need that much? Since it will be on pretty much 24/7 the more efficient it is the better. I figure that at some point id buy a newer more cost saving one than this old one I have but the question remains, does a higher watt PSU draw use a lot more power even if the demand isn't there?


Thanks for your time!
 

Zerk2012

Titan
Ambassador
This is probably a dumb question to ask but I wanted to make sure. I am finishing up a basic home server for myself that will be used for mostly data storage on my home network and for streaming movies. The calculated wattage I would need with my setup is 285 watts of power for a PSU. I have an older 600 watt PSU that I'm going to use but my question is will a lower wattage PSU be better for efficiency, (less power draw overall). Or would it not really matter if the demand isn't there because the system wouldn't need that much? Since it will be on pretty much 24/7 the more efficient it is the better. I figure that at some point id buy a newer more cost saving one than this old one I have but the question remains, does a higher watt PSU draw use a lot more power even if the demand isn't there?


Thanks for your time!
It would pull the same amount of watts and use about the same if you had a 400 watt power supply or a 1000 watt power supply.
 
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jay32267

Illustrious
"Or would it not really matter if the demand isn't there because the system wouldn't need that much? "

^^^You are somewhat going down the right road with this,

Being your load is fixed...the efficiency is going to depend on the efficiency of the supply you use AT THAT LOAD.

This changes from supply to supply.

Basically to get the best efficiency....you would find the PSU that is most efficient AT 285 WATTS.
 
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hotaru.hino

Respectable
Sep 1, 2020
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A few points:
  • Wattage calculators assume everything in the system is going to be taxed. A home server is likely not going to be doing much at all if anything most of the time so the actual power consumption over time is going to be much lower
  • Power supplies have hill-like efficiency curve, with 50% usage being where the hill caps out at. However, 80PLUS (except for Titanium I believe) starts at 30% utilization. But the absolute amount of watts you're losing at lower utilization isn't going to be enough to matter most of the time.
  • In the end however, lower utilization is better overall as higher utilization leads to higher temperatures, which accelerate the aging of electronics. But you also have to factor in if it's worth getting something that's, for all intents and purposes, overkill.
 
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Jul 10, 2020
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Cool, thanks everyone for the replies, that answers my question! At some point down the road I'll invest in a better more efficient PSU but for now I'll use my older one to get things setup.
 
Last edited:
A psu will use what power is demanded of it, regardless of the max capability.
A psu will operate most efficiently in the middle third of it's range.
Then, bronze, silver,gold,platinum ratings come into play.
Unless you are a crypto miner, the savings on better efficiency do not amount to much.
The most important selection criteria for a psu, once you have sufficient wattage is quality.
 
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