I have a server that operates 24.7. It occurred to me that I may be able to save some money on electricity bills if I could reduce its power consumption. It already has a low power AMD Sempron LE-1100 CPU so the power draw of the system should be quite low, mas o PSU is quite old and not especially efficient. This got me thinking about Power supplies designed for low power systems. There are plenty of 80+ certified PSU’s out there with 500+ watt ratings, but are these actually worth the investment for a low power system?
My system spends most of its time idle so I decided I’d work out the power draw would be if I were to build a new system with current components to do it’s job..
|Base system (por exemplo. atom or Core i5)||18W|
|4x 2Tb (por exemplo. Samsung EcoGreen F3)||19W|
|RAID Cartão (por exemplo. Areca 1220)||5W|
|1x 120mm Case / HDD Fan (por exemplo. Nexus Real Silent 120mm)||1W|
Using the above figures, I estimate that a new system with a similar role and capability to what I have will consume just under 45watts at idle.
For a typical low spec (450w) PSU, this load is only 10%. At this low a load a typical PSU can be quite inefficient. o ATX specification requires 70% efficiency at 20% of rated power, but a 43W draw is below 20% rated power for all PSU’s rated for 250W or above (in effect all PSU'S). Below is a comparison between a bare minimum ATX PSU and a few highly efficient PSU'S.
The figure for the generic PSU is based on the minimum requirement and is therefore a worst case. Even with a very poor efficiency PSU the AC draw from the wall won’t increase as the DC draw decreases. I have calculated a best-case yearly saving, based on a kWh charge of 10p and assuming 24.7 usage.
|Make / Model||Efficiency at 43W||leste. Total power draw (idle)||Saving|
|ATX v2.2 250w ATX||70% (at 50W)||61W|
|Seasonic X‑400||80.4% (at 42.6W)||53W||£6.97|
|Corsair AX850||77.3% (at 43W)||55W||£5.09|
|Enermax Modu87+ 500w||77.5% (at 43.4W)||56W||£5.21|
|Corsair CX400W||73.2% (at 43.2W)||59W||£2.35|
|Sparkle Power SPI220LE FlexATX 220W||80.5% (at 42.4w)||53W||£7.02|
|HuntKey Jumper R90 300W 80+ Gold||85% (at 30w)||51W||£9.50|
Conclusion: For a low power system it is cheaper, and probably more environmentally sound to keep (or re-use) an existing power supply than to replace it with a high power model, even if the new model is very efficient.
Corrected a calculation error and added the HuntKey Jumper R90. Even a very good value, highly efficient PSU can’t change the conclusion much in this scenario — the savings are just far too small to justify the cost (and environmental cost) of a new PSU. The HuntKey would take in excess of 3 years to pay for itself, and this is in an ideal scenario, compared to a a worth case scenario PSU! For an even lower power system (por exemplo. a AMD E350) the savings would be lower still. Even a “perfect” PSU would only net savings of around £16 a year!
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