0PSU LogoPSU Efficiency 4 — Modern gaming PC

This art­icle on PSU effi­ciency for a mod­ern sandy bridge gam­ing PC fol­lows on from 3 pre­vi­ous art­icles, about PSU effi­ciency for a medi­um power serv­er, a medi­um use very high power gam­ing PC and a low power serv­er or HTPC.

In this art­icle I’m going to assume the sys­tem is oper­ated from 4pm — 10pm week­days and 10am — 11pm week­ends at full power.  I’m also going to assume the sys­tem is on and idle for the rest of the time.

The sys­tem in ques­tion pulls ~45w idle and ~247w under full load.  I’m assum­ing an AMD Radeon HD 6870 (18w idle, 163w full) instead of the EN9400GT (11w idle, 23w full), the power num­bers are adjus­ted accord­ingly.  All of these estim­ates are delib­er­ately on the high side. I expect a typ­ic­al PC will spend more time off, more time idle, and wont be loaded as intensely as the example.

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.

Make / ModelEffi­ciency at idle
Effi­ciency at load
Est. A.C. power draw
Est. A.C. power draw
ATX v2.2 400w65% (at 45w)70% (at 247w)69W353W
Season­ic X‑40080.4% (at 42.6w)91% (at 248.4w)56W271W£31.43
Cor­sair AX85077.3% (at 43w)90.4% (at 251w)58W273W£29.70
Ener­max Modu87+ 500w77.5% (at 43.4w)90.5% (at 250.6w)58W273W£29.88
Cor­sair CX400W73.2% (at 43.2w)85.5% (at 250.6w)61W289W£23.14
King­win Lazer Plat­in­um 550W83.2% (at 41.6w)93.8% (at 248.6w)54W263W£34.89
HuntKey Jump­er R90 300W 80+ Gold88% (at 60W)89% (at 250w)51W281W£32.59

The con­clu­sion is no longer clear.  The value of an upgrade has improved over the pre­vi­ous scen­ario with a gam­ing PC.  How­ever, even with a lot of heavy use, and com­par­ing the most effi­cient PSU’s with the worst a budget ATX PSU can per­form, a new PSU will still take around 4 years to pay for itself.  A real world upgrade is unlikely to net this much saving.

If you are con­sid­er­ing repla­cing an exist­ing PSU my advice would be not to both­er, unless you have addi­tion­al reas­ons. If you are buy­ing new then it is worth pay­ing more for a bet­ter PSU, with­in reas­on. Of course if you want the effi­ciency for oth­er reas­ons (low noise, low heat) then those factors may make the value dif­fer­ence irrelevant.

Update (25-Dec-2011)

Cor­rec­ted slight error for Modu87+ and added the HuntKey Jump­er R90.  This PSU changes the con­clu­sion for any­one with a low effi­ciency PSU.  It pro­duces sav­ings of over £30, which is approx­im­ately the price of the PSU!  A pay­back peri­od of 1 year, with an expect­a­tion that elec­tri­city prices will con­tin­ue to rise is well worth the investment.

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