Testing (Cont’d)

Power Factor (PF)

Power factor is one of those mysterious properties of AC that even most electrical engineers have a hard time explaining.  A thorough technical discussion goes beyond the scope of this review (not to mention this author’s understanding).  For a more detailed discussion about PF, please look here.

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AC Volts x AC Amps = VA (Volt Amp)

Purely Resistive AC Load: VA = Watts (same as DC circuits)

Inductive/Reactive AC Load: VA x PF = Watts

AC Volts x AC Amps x PF = Watts

Power factor is defined as the ratio of true power (measured in watts) to apparent power (measured in Volt Amps).  It measures how effectively AC power is being used by a device.  The difference between true power and apparent power is expressed as the power factor and results from the way true power and apparent power are measured.  Ideally we would like to have true power and apparent power equal to one another, which would result in a PF of 1.00 or 100% effective power utilization. 

I measured the AC Power Factor with an Extech power analyzer.  All of the Thermaltake Toughpower power supplies incorporate active power factor correction circuits.

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The efficiency of a power supply is defined by the power output divided by the power input and is expressed as a percentage.  If a PSU were a 100% efficient (which none are) 600 watts of AC power going in would result in 600 watts of DC power coming out.  In the real world there are always inefficiencies and power is lost in the form of heat during the conversion process.

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The latest revisions to the ATX12V Power Supply Design Guide V 2.2 have continued to increase the efficiency recommendations for PC switching mode power supplies.  And the latest revision (Ver 2.2) now lists both required and recommended minimum efficiencies.

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I measured the AC power input to the power supply with an Extech power analyzer and calculated the combined DC power output by summing the products of all the outputs (volts x amps) for the different loads.

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The overall efficiency of the Thermaltake 850W power supply was excellent, and easily exceeded the new ATX design recommendation of 80% under a typical load.  Better efficiency translates to lower operating costs.  Note: all tests were performed while operating on 115 VAC.  The overall efficiency will most likely be a few percent higher when operating on 230 VAC, which would closely match Thermaltake’s claim of up to 87% efficient.

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The 80 Plus Computer Power Supply Program

There is a growing awareness among users, PC manufacturers and electric utilities regarding the money and natural resources that could be saved by adopting higher efficiency power supplies.  One group that is spearheading this new movement is Ecos Consulting.  You can learn more about their efforts to promote power supplies with better than 80% efficiency by visiting the 80 Plus Program website.

Spending a little more money up front to purchase a high efficiency power supply may very well pay for itself over the lifetime of the PC… 🙂

Differential Temperature and Noise Levels

The differential temperature across the Thermaltake power supply was calculated by subtracting the ambient room air temperature (T in) from the temperature of the warm exhaust air flowing out of the power supply (T out).  Thermocouples were placed at the air inlet and exhaust outlet of the power supply.  The ambient room air temperature was 24ºC (75ºF) +/- 0.5ºC during testing.

T in = temperature of air entering power supply

T out = temperature of air exhausting from power supply

ΔT = T out – T in

The Toughpower 850W power supply uses a single temperature-controlled fan that speeds up as the load (internal heat generation) increases.

Sound pressure level readings were taken 3′ in front of the PSU in an otherwise quiet room.  The power supply was placed on a foam rubber mouse pad during testing.  The ambient noise level was ~30 dBA.  The sound level meter used for these tests is only calibrated down to 35 dBA.  All readings below this were recorded as <35 dBA.  In my opinion this is very quiet and would not be noticed over normal case fan and hard disk drive noise.  Note: I was not able to record SPL readings at maximum output because all the little cooling fans in the DC loads where all running.

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The Toughpower 850W power supply was relatively quiet while operating under light loads, but the fan quickly became noticeable as the output power approached 500 watts and became quite loud at full load.  One of the big differences between the Toughpower 750W and 850W models is the fan.  The Toughpower 850W uses a high-speed version of the same Yate Loon Electronics fan that is used in the Toughpower 750W.  More power requires more cooling, and in this case more cooling translates to higher fan speed and more noise.

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